摘要:

Contents 3663 3669 3675 3683 3693 370 1 3709 3717 3725 3737 Normal and Abnormal Electron Spin Resonance Spectra of Low-spin Cobalt(r1) IN,]-Macrocyclic Complexes. A Means of Breaking the Co-C Bond in B12 Co-enzyme M. Green, J. Daniels and L. M. Engelhardt The Interaction between Superoxide Dismutase and Doxorubicin. An Electron Spin Resonance Approach V. Malatesta, F. Morazzoni, L. Pellicciari-Bollini and R. Scotti Biomolecular Dynamics and Electron Spin Resonance Spectra of Copper Complexes of Antitumour Agents in Solution. Part 2.-Rifamycins R. Basosi, R. Pogni, E. Tiezzi, W. E. Antholine and L. C. Moscinsky An Electron Spin Resonance Investigation of the Nature of the Complexes formed between Copper(I1) and Glycylhistidine D. B. McPhail and B. A. Goodman A Vibronic Coupling Approach for the Interpretation of the g-Value Temperature Dependence in Type-I Copper Proteins M.Bacci and S. Cannistr aro The Electron Spin Resonance Spectrum of Al[C,H,] in Hydrocarbon Matrices J. A. Howard, B. Mile, J. S. Tse and H. Morris N; and (CN); Spin-Lattice Relaxation in KCN Crystals H. J. Kalinowski and L. C. Scavarda do Carmo Single-crystal Proton ENDOR of the SO, Centre in y-Irradiated Sulphamic Acid N. M. Atherton, C. Oliva, E. J. Oliver and D. M. Wylie Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice 1,. Part 1.-The 0- Radicals Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice I,. Part 2.-The HO, Radicals J. Bednarek and A. Plonka J. Bednarek and A. PlonkaContents 3663 3669 3675 3683 3693 370 1 3709 3717 3725 3737 Normal and Abnormal Electron Spin Resonance Spectra of Low-spin Cobalt(r1) IN,]-Macrocyclic Complexes.A Means of Breaking the Co-C Bond in B12 Co-enzyme M. Green, J. Daniels and L. M. Engelhardt The Interaction between Superoxide Dismutase and Doxorubicin. An Electron Spin Resonance Approach V. Malatesta, F. Morazzoni, L. Pellicciari-Bollini and R. Scotti Biomolecular Dynamics and Electron Spin Resonance Spectra of Copper Complexes of Antitumour Agents in Solution. Part 2.-Rifamycins R. Basosi, R. Pogni, E. Tiezzi, W. E. Antholine and L. C. Moscinsky An Electron Spin Resonance Investigation of the Nature of the Complexes formed between Copper(I1) and Glycylhistidine D. B. McPhail and B. A. Goodman A Vibronic Coupling Approach for the Interpretation of the g-Value Temperature Dependence in Type-I Copper Proteins M. Bacci and S. Cannistr aro The Electron Spin Resonance Spectrum of Al[C,H,] in Hydrocarbon Matrices J. A. Howard, B. Mile, J. S. Tse and H. Morris N; and (CN); Spin-Lattice Relaxation in KCN Crystals H. J. Kalinowski and L. C. Scavarda do Carmo Single-crystal Proton ENDOR of the SO, Centre in y-Irradiated Sulphamic Acid N. M. Atherton, C. Oliva, E. J. Oliver and D. M. Wylie Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice 1,. Part 1.-The 0- Radicals Single-crystal Electron Spin Resonance Studies on Radiation-produced Species in Ice I,. Part 2.-The HO, Radicals J. Bednarek and A. Plonka J. Bednarek and A. Plonka

ISSN:0300-9599    

DOI:10.1039/F198783FX041

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

Electrochemistry Group Workshop on Electrochemical Techniques and Instruments To be held at the University of Warwick on 6-7 January 1988 Further information from Dr P. N. Bartlett, Department of Chemistry, University of Warwick, Coventry CV4 7AL Surface Reactivity and Catalysis Group with the Process Technology Group and the Institute of Chemical Engineers Opportunities for Innovation in the Application of Catalysis To be held at Queen Mary College, London on 6-7 January 1988 Further information from Professor J. Pritchard, Queen Mary College, London Division with the Institute of Mathematics and its Applications Mathematical Modelling of Semiconductor Devices and Processes To be held at the University of Loughborough on 7-8 January 1988 Further information from the Institute of Mathematics, Maitland House, Warrior Square, Southend-on-Sea SS1 2JY Division London Symposium: Modern Electrochemical Systems To be held at Imperial College, London on 12 January 1988 Further information from Mrs Y.A. Fish, Royal Society of Chemistry, Burlington House, London W1V OBN Polymer Physics Group with the 3Ps Group Plastics, Packaging and Printing To be held at the Institute of Physics, 47 Belgrave Square, London on 18 February 1988 Further information from Dr M. Richardson, National Physical Laboratory, Teddington, Middlesex l w 1 1 OLW Theoretical Chemistry Group Postgraduate Students’ Meeting To be held at University College, London on 2 March 1988 Further information from Dr G. Doggett, Department of Chemistry, University of York, York Colloid and Interface Science Group with The Society of Chemical Industry and British Radio frequency Spectroscopy Group Spectroscopy in Colloid Science To be held at the University of Bristol on 5-7 April 1988 Further information from Dr R. Buscall, ICI Corporate Colloid Science Group, PO Box 11, The Heath, Runcorn WA7 40E Annual Congress: Division with Electrochemistry Group Solid State Materials in Electrochemistry To be held at the University of Kent, Canterbury on 12-15 April 1988 Further information from Dr J.F. Gibson, Royal Society of Chemistry, Burlington House, London W1V OBN Electrochemistry Group with The Society of Chemical Industry Electrolytic Bubbles To be held at Imperial College, London on 31 May 1988 Further information from Professor W. J. Albery, Department of Chemistry, Imperial College of Science and Technology, South Kensington, London SW7 2AY Electrochemistry Group with The Society of Chemical Industry Chlorine Symposium To be held at the Tara Hotel, London on 1-3 June 1988 Further information from Dr S.P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GLI 3 9BP Gas Kinetics Group Xth International Symposium on Gas Kinetics To be held at University College, Swansea on 24-29 July 1988 Further information from Dr G. Hancock, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 302 (xiii)Electrochemistry Group Workshop on Electrochemical Techniques and Instruments To be held at the University of Warwick on 6-7 January 1988 Further information from Dr P.N. Bartlett, Department of Chemistry, University of Warwick, Coventry CV4 7AL Surface Reactivity and Catalysis Group with the Process Technology Group and the Institute of Chemical Engineers Opportunities for Innovation in the Application of Catalysis To be held at Queen Mary College, London on 6-7 January 1988 Further information from Professor J. Pritchard, Queen Mary College, London Division with the Institute of Mathematics and its Applications Mathematical Modelling of Semiconductor Devices and Processes To be held at the University of Loughborough on 7-8 January 1988 Further information from the Institute of Mathematics, Maitland House, Warrior Square, Southend-on-Sea SS1 2JY Division London Symposium: Modern Electrochemical Systems To be held at Imperial College, London on 12 January 1988 Further information from Mrs Y.A. Fish, Royal Society of Chemistry, Burlington House, London W1V OBN Polymer Physics Group with the 3Ps Group Plastics, Packaging and Printing To be held at the Institute of Physics, 47 Belgrave Square, London on 18 February 1988 Further information from Dr M. Richardson, National Physical Laboratory, Teddington, Middlesex l w 1 1 OLW Theoretical Chemistry Group Postgraduate Students’ Meeting To be held at University College, London on 2 March 1988 Further information from Dr G. Doggett, Department of Chemistry, University of York, York Colloid and Interface Science Group with The Society of Chemical Industry and British Radio frequency Spectroscopy Group Spectroscopy in Colloid Science To be held at the University of Bristol on 5-7 April 1988 Further information from Dr R.Buscall, ICI Corporate Colloid Science Group, PO Box 11, The Heath, Runcorn WA7 40E Annual Congress: Division with Electrochemistry Group Solid State Materials in Electrochemistry To be held at the University of Kent, Canterbury on 12-15 April 1988 Further information from Dr J. F. Gibson, Royal Society of Chemistry, Burlington House, London W1V OBN Electrochemistry Group with The Society of Chemical Industry Electrolytic Bubbles To be held at Imperial College, London on 31 May 1988 Further information from Professor W. J. Albery, Department of Chemistry, Imperial College of Science and Technology, South Kensington, London SW7 2AY Electrochemistry Group with The Society of Chemical Industry Chlorine Symposium To be held at the Tara Hotel, London on 1-3 June 1988 Further information from Dr S. P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GLI 3 9BP Gas Kinetics Group Xth International Symposium on Gas Kinetics To be held at University College, Swansea on 24-29 July 1988 Further information from Dr G. Hancock, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 302 (xiii)

ISSN:0300-9599    

DOI:10.1039/F198783BX043

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

ISSN 0300-9238 JCFTAR 83 (1 1 ) 3229-3468 (1 987) JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions I Physical Chemistry in Condensed Phases 3239 3237 3249 3259 327 1 3283 3295 3303 3317 333 1 3345 3355 3367 3383 3399 3415 3419 3429 3447 3459 111- CONTENTS Effusion Mass Spectrometric Determination of Thermodynamic Properties of the Gaseous Mono- and Di-hydroxides of Calcium and KCaO(g) M. Farber, R. D. Srivastava, J. W. Moyer and J. D. Leeper The Inclusion of Pyronine Y by 8- and ;:-Cyclodextrin. '4 Kinetic and Equilibrium Study Thermodynamic Properties of Concentrated Heteroionic Polyelectrolyte Solu- tions H. R. Corti Transport Phenomena in Concentrated Aqueous Solutions of Sodium-Caesium Polystyrene Sulphonates H. R. Corti Hydrazine Reduction of Transition-metal Oxides D.M. Littrell, D. H. Bowers and B. J. Tatarchuk Infrared Study of the Adsorption of Non-ionic Surfactants on Silica Y. Lijour, J-Y. Calves and P. Saumagne Infrared Study of the Desorption of Polycondensed Aromatic Compounds by Non-ionic Surfactants at the Silica-Carbon Tetrachloride Interface Y. Lijour, J-Y. Calves and P. Saumagne ActiL ity and Selectivity in Toluene Oxidation on Well Characterized Vanadium Oxide Catalysts K. Mori, A. Miyamoto and Y. Murakami One-dimensional Rare Gases in the Pores of Ferrierite and their Virial Coefficients Micelle Formation of Ionic Amphiphiles I. Johnson, G . Olofsson and B. Jonsson The Mechanism of Conductivity of Liquid Polymer Electrolytes G . G. Cameron, M. D. Ingram and G. A. Sorrie Wetting of Graphite (0001) by Carbon Monoxide. A Stepwise Adsorption Isotherm Study A New Analytical Solution of the Quaternary Gibbs-Duhem Equation Z-C.Wang Tin Oxide Surfaces. Part 17.-An Infrared and Thermogravimetric Analysis of the Thermal Dehydration of Tin(1v) Oxide Gel P. G. Harrison and A. Guest Radiotracer Studies on Chemisorption on Copper-based Catalysts. Part 1 .-The Adsorption of Carbon Monoxide and Carbon Dioxide on Copper/Zinc Oxide/ Alumina and Related Catalysts One-electron Reduction of 2,2'-Bipyrimidine in Aqueous Solution K. Barqawi, T. S. Akasheh, B. J. Parsons and P. C. Beaumont Ion-pair Formation by Tetra-alkylammonium Ions in Methanol. A Nuclear Magnetic Resonance Study The Ferroelectric and Liquid-crystalline Properties of Some Chiral Alkyl 4-n- Alkanoyloxybiphenyl-4'-carboxylates .J.W. Goodby, E. Chin, J. M. Geary, J. S. Patel and P. L. Finn Structure of Second-stage Graphite-Rubidium. C,,Rb G. R. S. Naylor and J. W. White Investigation of Internal Silanol Groups as Structural Defects in ZSM-5-type Zeolites M. Hunger, J. Karger, H. Pfeifer, J. Caro, B. Zibrowius, M. Bulow and R. Mostowicz R. L. Schiller, S. F. Lincoln and J. H. Coates T. Takaishi, K. Nonaka and T. Okada Y. Larher, F. Angerand and Y. Maurice S. Kinnaird, G. Webb and G. C. Chinchen !W. Krell, M. C. R. Symons and J. Barthel F A R IISSN 0300-9238 JCFTAR 83 (1 1 ) 3229-3468 (1 987) JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions I Physical Chemistry in Condensed Phases 3239 3237 3249 3259 327 1 3283 3295 3303 3317 333 1 3345 3355 3367 3383 3399 3415 3419 3429 3447 3459 111- CONTENTS Effusion Mass Spectrometric Determination of Thermodynamic Properties of the Gaseous Mono- and Di-hydroxides of Calcium and KCaO(g) M.Farber, R. D. Srivastava, J. W. Moyer and J. D. Leeper The Inclusion of Pyronine Y by 8- and ;:-Cyclodextrin. '4 Kinetic and Equilibrium Study Thermodynamic Properties of Concentrated Heteroionic Polyelectrolyte Solu- tions H. R. Corti Transport Phenomena in Concentrated Aqueous Solutions of Sodium-Caesium Polystyrene Sulphonates H. R. Corti Hydrazine Reduction of Transition-metal Oxides D. M. Littrell, D. H. Bowers and B. J. Tatarchuk Infrared Study of the Adsorption of Non-ionic Surfactants on Silica Y. Lijour, J-Y. Calves and P. Saumagne Infrared Study of the Desorption of Polycondensed Aromatic Compounds by Non-ionic Surfactants at the Silica-Carbon Tetrachloride Interface Y.Lijour, J-Y. Calves and P. Saumagne ActiL ity and Selectivity in Toluene Oxidation on Well Characterized Vanadium Oxide Catalysts K. Mori, A. Miyamoto and Y. Murakami One-dimensional Rare Gases in the Pores of Ferrierite and their Virial Coefficients Micelle Formation of Ionic Amphiphiles I. Johnson, G . Olofsson and B. Jonsson The Mechanism of Conductivity of Liquid Polymer Electrolytes G . G. Cameron, M. D. Ingram and G. A. Sorrie Wetting of Graphite (0001) by Carbon Monoxide. A Stepwise Adsorption Isotherm Study A New Analytical Solution of the Quaternary Gibbs-Duhem Equation Z-C. Wang Tin Oxide Surfaces. Part 17.-An Infrared and Thermogravimetric Analysis of the Thermal Dehydration of Tin(1v) Oxide Gel P.G. Harrison and A. Guest Radiotracer Studies on Chemisorption on Copper-based Catalysts. Part 1 .-The Adsorption of Carbon Monoxide and Carbon Dioxide on Copper/Zinc Oxide/ Alumina and Related Catalysts One-electron Reduction of 2,2'-Bipyrimidine in Aqueous Solution K. Barqawi, T. S. Akasheh, B. J. Parsons and P. C. Beaumont Ion-pair Formation by Tetra-alkylammonium Ions in Methanol. A Nuclear Magnetic Resonance Study The Ferroelectric and Liquid-crystalline Properties of Some Chiral Alkyl 4-n- Alkanoyloxybiphenyl-4'-carboxylates .J. W. Goodby, E. Chin, J. M. Geary, J. S. Patel and P. L. Finn Structure of Second-stage Graphite-Rubidium. C,,Rb G. R. S. Naylor and J. W. White Investigation of Internal Silanol Groups as Structural Defects in ZSM-5-type Zeolites M. Hunger, J. Karger, H. Pfeifer, J. Caro, B. Zibrowius, M. Bulow and R. Mostowicz R. L. Schiller, S. F. Lincoln and J. H. Coates T. Takaishi, K. Nonaka and T. Okada Y. Larher, F. Angerand and Y. Maurice S. Kinnaird, G. Webb and G. C. Chinchen !W. Krell, M. C. R. Symons and J. Barthel F A R I

ISSN:0300-9599    

DOI:10.1039/F198783FP145

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

1941 1957 1975 I985 201 1 2025 203 5 2045 2053 2067 2073 208 1 2097 21 13 2123 JOURNAL OF THE CHEMICAL SOCIETY Faraday Transactions II, Issue I I , 1987 Molecular and Chemical Physics For the benefit of readers of Faraday Transactions I, the contents list of Faraday Transactions 11, Issue 11, is reproduced below. Time-resolved Fluorescence of p-Dimethylaminobenzonitrile in Mixed Solvents S. R. Meech and D. Phillips Polyatomic London Dispersion Forces J. Homer and M. S. Mohammadi Bonded-atom Properties and the Inert Gases J. Homer and M. S. Mohammadi Viscosity and Self-diffusion of Simple Liquids. Hard-sphere Treatment of Molecular Dynamics Data Laser-induced Fluorescence and Vibrational Relaxation of the Phenyl Nitrene Radical Some Gas-phase Ion-Molecule Reactions of Acetone J.A. Hunter, C. A. F. Johnson, I. J. M. McGill, J. E. Parker and G. P. Smith Homogeneous Decomposition of Dialkylperoxides in Oxygen K. A. Sahetchian, R. Rigny, N. Blin and A. Heiss D. M. Heyes G. Hancock and K. G. McKendrick The Quenching of O,(b Z:) at High Temperatures. Kinetics, Sensitivity Analysis and Corrections Quinney P. M. Borrell, P. Borrell, D. S. Richards and D. Barrier Permeabilities for Kinetic Isotope Effects Neopentane by Hydrogen T. Gaumann 1 a Symmetric Eckart Potential as studied by the for Hydrogen/Deuterium Abstraction from Atoms in the Gas Phase N. Fujisaki, A. Ruf and Electric Reaction Field of a Molecular Octopole and the Solvent Proton Chemical Shift of Methane M. Huizinga, H. A. W. Ragas, B. H. J. Schrijvers and J. Biemond Absolute Determinations of the Kinetics and Temperature Dependences of the Reactions of OH with a Series of Alkynes R.B. Boodaghians, I. W. Hall, F. S. Toby and R. P. Wayne Modelling of Transient Production and Decay following Laser Excitation of Opaque Materials A Molecular Dynamics Study of the Rotator Phase of t-Butyl Bromide M. Ferrario, M. L. Klein, R. M. Lynden-Bell and I. R. McDonald Molecular Structure of Methyl-2-nitrophenyl Sulphide. An Electron Diffraction Study Gy. Schultz, I. Hargittai, I. Kapovits and A. Kucsman 14N Quadrupole Double Resonance in 2-, 3- and 4-Nitrobenzoic Acids D. Stephenson and J. A. S. Smith D. Oelkrug, W. Honnen, F. Wilkinson and C. J. Willsher2 133 21 39 The Structure and Energetics of the C,N+ Ion P. W. Harland and R. G. A. R.Maclagan Potential-energy Curves of the Torsional Mode of 1,l '-Binaphthyl in the Ground and Lowest Excited Singlet States. A CS-INDO/CI Study I. Baraldi, G. Ponterini and F. Momicchioli Change of the Electronic Structures of Tetrakis(alky1thio)tetrathiafulvalenes (TTC,-TTFs) during the Solid-Melt Transition H. Yamamoto, K. Seki, H. Inokuchi and G. Saito Determination of Oscillation Amplitudes and Force Constants in Hydrogen- bonded Dimers from Nuclear Quadrupole Hyperfine Coupling Constants P. Cope, D. J. Millen and A. C. Legon Arrhenius Parameters for the Addition of HO, Radicals to Pent-1-ene, Hex- 1-ene and cis- and trans-Hex-2-ene over the Range 400-520 "C S. K. Gulati, S. Mather and R. W. Walker Reviews of Books 2 15 1 2 163 2171 2181 D. M. Hirst; G. Duxbury; R.A. Kennedy The following papers were accepted for publication in Faraday Transactions I during August 1987. 6/ 1688 612439 7/27 1 71293 71375 71452 7/520 7/586 71635 7/654 On the Relationship between Interactions at the Ionic Crystal/ Water Inter- face and the Elementary Events of Crystal Growth and Dissolution V. K. W. Cheng, B. A. W. Coller and E. R. Smith A Study in Preferential Solvation using a Solvatochromic Pyridinium Betaine J. G. Dawber, J. Ward and R. A. Williams Hydrogenolysis of Ethane. Part 2.-Initial Rate Measurements over Ni and Pd Catalysts S. Kristyan and J. Szamosi Photoluminescence Properties of MgO Powders with Coordinatively Unsaturated Surface Ions M. Anpo, Y. Yamada, Y. Kubokawa, S. Coluccia, A. Zecchina, M. Che and C. Louis Measurements of Electrolyte Conductivity of Alkali-metal Perchlorates and LiNO, in Acetone at 25 "C N.Schmelzer, J. Einfeldt and M. Grigo Application of Kirkwood-Buff Theory to Free Energies of Electrolytes from One Solvent to Another A. K. Covington and K. E. Newman On the Association and Solvation of Formamide in Pyridine and Picolines P. P. Singh Effect of Polymer Backbone on the Ligand Substitution Reaction of Macromolecule-Metal Complex. Acid and Base Hydolyses of the Polymer- bound Cobalt(rI1) Complexes Y. Kurimura, Y. Takagi and T. Saito Structure and Reactivity of Zn-Cr Mixed Oxides. Part 1.-The Role of Non-stoichiometry on Bulk and Surface Properties M. Bertoldi, G. Busca, B. Fubini, E. Giamello, F. Triffirb and A. Vaccari The Brusselator: It does Oscillate all the Same R.Lefever, G. Nicolis and P. Borckmans (ii)71685 717 18 71745 7/99 1 71992 7/ 1043 7/ 1046 7/ 1067 7/ 1068 7/ 1078 7/ 1090 711 128 711154 711 155 7/ 1242 Correlations among the Wavenumbers of Skeletal Vibrations, Unit Cell Size and Molar Fraction of Aluminium of Y Zeolites. Removal of Non-skeletal A1 Species with H,Na,EDTA L. Kubelkova, V. Seidi, G. Borbely and K. Beyer A Conductance Study of the Tetra-alkylammonium Bromides in 2-Methoxy- ethanol at 25 "C D. Das Gupta, S. Das and D. K. Hazra Photosensitisation of Melanins Covalently Bound to Dyes J. Bielec, B. Pilas, T. Sarna, C. Knox and T. G. Truscott Time-resolved Analysis of ' Crystal-like ' Structure-forming Process of a Monodisperse Polystyrene Sphere as studied by the Rapid-scanning Spectrophotometry T.Okubo Deformation of ' Crystal-like ' Structure of a Monodisperse Polystyrene Sphere under Shear Rate as studied by the Transmitted-light Spectrum Method T. Okubo PuOz(c) + U4+(aq) Reaction in Nitric Acid A. Inoue Aggregation in Aqueous Solutions of Poly(viny1 alcohol) N. J. Crowther and D. Eagland Combined Study of Coagulation Kinetics and Close-range Aggregate Structure Third-body Interactions in the Oscillatory Oxidation of Hydrogen in a Well Stirred Flow Reactor D. L. Baulch, J. F. Griffiths, A. J. Pappin and A. F. Sykes Optical Investigation of Short-chain n-Alkanes Z. Blaszczak and P. Gauden Solubilities of Salts and Kinetics of Reactions involving Inorganic Complex Ions in Aqueous Acetone Mixtures. Derivation of Transfer Chemical Potentials for Ions in these Aqueous Mixtures at Ambient Pressure and 298.2 K M.J. Blandamer, B. Briggs, J. Burgess, P. Guardado, S. Radulovic and C. D. Hubbard Liquid Structure and Second-order Mixing Functions for 1 -Chloro- naphthalene with Linear and Branched Alkanes M. Costas, H. V. Tra, D. Pattr?rson, M. Caceres-Alonso, G. Tardajos and E. Aicart Study of the Conformational Equilibria between Rotational Isomers using Ultrasonic Relaxation and Raman Spectroscopies. Part 2.-Di- and Tri- halogenoalkanes Coalescence Stability of Emulsion-sized Droplets at a Planar Oil-Water Inter- face and the Relationship to Protein Film Surface Rheology E. Dickinson, B. S. Murray and G. Stainsby The Formation of fi-Muonium-substituted Cyclopentyl and Cyclopheptyl Radicals, and the Significance of the Ap/Ap Isotope Ratio in Relation to the Conformations of Muonium-substituted Alkyl Radicals C.J. Rhodes and M. C. R. Symons A. Lips and R. M. Duckworth H. Nomura, S. Koda and K. Hamada (iii)Cumulative Author Index 1987 Abraham, M. H., 2867 Agnel, J-P. L., 225 Aika, K., 3139 Akalay, I., 1137 Akasheh, T., 2525, 3415 Akitt, J. W., 1725 Albano, K., 21 13 Alberti, A., 91 Albery, W. J., 2407 Alexandrova, I., 2841 Ali, A.-K. M., 2391 Allen, G. C., 925, 1355 Amorebieta, V. T., 3055 Andersen, A., 2140 Anderson, A. B., 463 Anderson, J. B. F., 913 Anderson, R. F., 3177 Angerand, F., 3355 Antholine, W. E., 151 Ardizzone, S., 1159 Arias, S., 2619 Arriaga, P., 2705 Atay, N. Z., 2407 Atherton, N. M., 37, 941, 3227 Aun Tan, S., 2035 Aveyard, R., 2347 Avnir, D., 1685 Axelsen, V., 107 Bahneman, D.W., 2559 Baker, B. G., 2136 Baldini, G., 1609 Ball, R. C., 2515 Balon, M., 1029 Barford, W., 2515 Barqawi, K., 3415 Barratt, M. D., 135 Barrer, R. M., 779 Barthel, J., 3419 Bartok, M., 2359 Basosi, R., 151 Bastein, A. G. T. M., 2103, 2129 Bastl, Z., 51 1 Bateman, J. B., 841 Battesti, C. M., 225 Baussart, H., 171 1 Beaumont, P. C., 3415 Becker, K. A., 535 Beezer, A. E., 2705 Bell, A. T., 2061, 2086, 2087, 2088, 3149 Bennett, J. E., 1805, 2421, 2433 Berclaz, T., 401 Berleur, F., 177 Bernal, S., 2279 Berroa de Ponce, H., 1569 Au, C-T., 2047 Berry, F. J., 615, 2573 Bertagnolli, H., 687 Berthelot, J., 231 Beyer, H. K., 511 Bianchi, H., 3027 Bianconi, A., 289 Binks, B. P., 2347 Bird, R., 3069 Bjorklund, R. B., 1507 Blandamer, M. J., 559, 865, 1783, 3039 Blyth, G., 751 Boerio-Goates, J., 1553 Bogge, H., 2157 Bond, G.C., 1963, 2071, 2088, 2129, 2130, 2133, 2138, 2140 Borbkly, G., 51 1 Botana, F. J., 2279 Boucher, E. A., 1269 Bowers, D. H., 3271 Brandreth, B. J., 1835 Brandt, B. A., 2857 Braquet, P., 177 Brazdil, J. F., 463 Breault, R., 2119 Brede, O., 2365 Brillas, E., 2619, 2813 Briscoe, B. J., 938 Bruce, J. M., 85 Brunton, G., 2421, 2433 Brustolon, M., 69 Brycki, B., 2541 Budil, D. E., 13 Bugyi, L., 2015 Bulow, M., 1843, 3459 Burch, R., 913, 2087, 2130, 2134, 2135, 2141, 2250 Burgess, J., 559, 865, 1783, 3039 Burggraaf, A. J., 1485 Burke, L. D., 299 Busca, G., 853, 1591, 2213 Buscall, R., 873 Butt, J. B., 2757 Cairns, J. A., 913 Calves, J-Y., 3283, 3295 Cameron, G. G., 3345 Care, C. M., 2905 Carley, A.F., 351 Caro, J., 1843, 2301, 3459 Carthy, G., 2585 Cassidy, J. F., 231 Celalyan-Berthier, A., 401 Chadwick, D., 2227 Chalker, P. R., 351 Chandra, H., 759 Chengyu, W., 2573 Chieux, P., 687 Chin, E., 3429 Chinchen, G. C., 2193, 3399 Chittofrati, A., 1159 Choudhery, R. A., 2407 Christensen, P. A., 3001 Christmann, K., 1975 Chu, G., 2533 Chudek, J. A., 2641 Clark, B., 865 Clausen, B. S., 2157 Clifford, A. A., 751 Coates, J. H., 2697, 2751, Colin, A. C., 819 Coller, B. A. W., 645, 657 Coluccia, S., 477 Colussi, A. J., 3055 Compostizo, A., 819 Compton, R. G., 1261 Conway, B. E., 1063 Copperthwaite, R. G., 2963 Corti, H. R., 3027, 3249, 3259 Corvaja, C., 57 Costa, J. M., 2619 Cottrell, M. R., 3039 Couillard, C., 125 Courbon, H., 697 Craven, J. B., 779 Crossland, W.A., 37 Cullis, C. F., 3227 Cumins, P. G., 2773 Cunningham, J., 2973 Czametzki, L., 3015 D’Alba, F., 267 Danil de Namor, A. F., 1569,2663 Darvell, B. W., 2953 Dash, A. C., 1307, 2505 Dash, N., 2505 Daverio, D., 705 Davies, M. J., 1347 Davoli, I., 289 Dawber, J. G., 771 Day, P., 3225 de Beer, V. H. J., 2145 De Doncker, J., 125 De Laet, M., 125 De Ranter, C. J., 257 Declerck, P. J., 257 Dega-Szafran, Z., 2541 Delafosse, D., 1137 Delahanty, J. N., 135 Delobel, R., 1711 Despeyroux, B. M., 2081, 2139, Chu, D-Y., 635 3237 2171, 2243, 2255AUTHOR INDEX Di Lorenzo, S., 267 Diaz Peiia, M., 819 DimitrijeviC, N. M., 1193 Dimov, A. D., 2841 Dodd, N. J. F., 85 Doddridge, B. G., 2697 Domen, K., 2765 Dongbai, L., 2573 Drew, M. G. B., 3093 Du, J., 2671 Duarte, M.A., 2133 Duce, P. P., 2867 Ducret, F., 141 Dudikova, L., 511 Dusaucy, A-C., 125 Dutkiewicz, E., 2847 Eicke, H.-F., 1621 Elbing, E , 645, 657 Elders, J. M., 1725 Empis, J. M. A., 43 Endoh, A., 411 Engberts, J. B. F. N., 865 Evans, J. C., 43, 135 Fahim, R. B., 1601 Fan, G., 323 Farber, M., 3229 Fatome, M., 177 Feakins, D., 2585 Fejes, P., 1109 Fernandez-Prini, R., 3027 Fierro, J. L. G., 3149 Finn, P. L., 3429 Fischer, C-H., 2559 Fitch, A.N., 3199 Fletcher, P. D. I., 985, 1493 Flint, N. J., 167 Formaro, L., 1159 Formosinho, S. J., 431 Forrester, A. R., 211 Forste, C., 2301 Forster, H., 1109 Foster, R., 2641 Fouassier, J. P., 2935 Fox, G. G., 2705 Fraissard, J., 451 Franchini, G. C., 3129 Freude, D., 1843 Freund, E., 1417 Fricke, R., 1041, 3115 Fujii, K., 675 Fujitsu, H., 1427 Fukada, S., 3207 Funabiki, T., 2883, 2895 Galli, P., 853 Gampp, H., 1719 Gao, Y., 2671 Garbowski, E., 1469 Garcia, R., 2279 Garrido, J., 1081 Garrido, J.A,, 2813 Garrone, E., 1237 Geary, J. M., 3429 Gellings, P. J., 1485 Geoffroy, M., 401 Germanus, A., 2301 Gervasini, A., 705, 2271 Giddings, S., 2317, 2331 Gilbert, B. C., 77 Gilbert, R. G., 1449 Goates, J. R., 1553 Goates, S. R., 1553 Goffredi, M., 1437 Golding, P. D., 1203, 2709, 2719 Goodby, J. W., 3429 Goodman, D. W., 1963, 1967, 2071, 2072, 2073, 2075, 2082, 2086, 2251 Goralski, P., 3083 Gottschalk, F., 571 Gozzi, D., 289 Grampp, G., 161 Grant, R. B., 2035 Gratzel, M., 1101 Grauer, G. L., 1685 Grauer, Z., 1685 Gray, P., 751 Greci, L., 69 Greenwood, P., 2663 Grieser, F., 591 Griffiths, J. F., 3226 Grigorian, K.R., 1189 Grimblot, J., 2170 Grossi, L., 77 Groves, G. S., 1119, 1281 Grzybkowski, W., 281, 1253, Gu, T., 2671 Guardado, P., 559 Guest, A., 3383 Guilleux, M.-F., 1137 Gunasekara, M. U., 2553 Hada, H., 1559 Hagele, G., 1055 Hakin, A. W., 559, 865, 1783, Halawani, K. H., 1281 Hall, D. G., 967 Hall, D. I., 2693 Hall, M. V. M., 571 Haller, G. L., 1965, 2072, 2080, 2089, 2091, 2129, 2131, 2132, 2133, 2135, 2136, 2137, 2138, 2243 226 1 3039 Halpern, A., 219 Hamada, K., 527 Hanke, V.-R., 2847 Harbach, C. A. J., 2035 Harendt, C., 1975 Harland, R. G., 1261 Harrer, W., 161 Harriman, A., 3001 Harris, R. K., 1055 Harrison, P. G., 3383 Hartland, G. V., 591 Hasegawa, A., 759, 2803 Hatayama, F., 675 Haul, R., 2083 Hayashi, K., 1795 Hayashi, O., 3061 Hayter, J. B., 2773 (v) Healy, C.P., 2973 Heatley, F., 517, 2593 Hemminga, M. A., 203 Henglein, A., 2559 Henriksson, U., 1515 Hermann, R., 2365 Herold, B. J., 43 Hertz, H. G., 687 Hidalgo, J., 1029 Higgins, J. S., 939 Hikmat, N. A., 2391 Hilfiker, R., 1621 Hill, W., 2381 Hinderman, J. P., 2119, 2142, Holden, J. G., 615 Holloway, S., 1935 Hongzhang, D., 2573 Hounslow, A. M., 2459, 2697 Howarth, J. N., 2787, 2795 Howe, A. M., 985, 1007 Howe, R. F., 813 Hudson, A., 91 Hunger, M., 1843, 3459 Hunter, R., 571 Hunter, W. H., 2705 Hussein, F. H., 1631 Hutchings, G. J., 571, 2963 Ichikawa, K., 2925 Ikeda, R., 3207 Ikeyama, N., 1427 Imamura, H., 743 Imanaka, T., 665 Ingram, M. D., 3345 Inoue, Y., 3061 Ishikawa, T., 2605 Ismail, H. M., 1601, 2835 Isobe, M., 3139 Isozumi,Y., , 2895 Ito, T., 451 Iwaki, T., 943, 957 Iwamoto, E., 1641 Jackson, S.D., 905, 1835 Jaenicke, W., 161, 2727 Janata, E., 2559 Janes, R., 383 JenE, F., 2857 Jerschkewitz, H-G., 3 1 15 Jobic, H., 3199 Johnson, I., 3331 Jones, P., 2735 Jonsson, B., 3331 Joyal, C. L. M., 2757 Joyner, R. W., 1945, 1965, 2074, 2085, 2138, 2249 Juszczyk, W., 1293 Kakuta, N., 1227, 2635 Kameda, Y., 2925 Kaneko, M., 1539 Kanno, T., 721 Kapturkiewicz, A., 2727 Karger, J., 1843, 2301, 3459 Kariv-Miller, E., 1169 Karpinski, Z., 1293 Katime, I., 2289 2143AUTHOR INDEX Kato, C., 1851 Kawaguchi, T., 1579 Kazansky, V. B., 2381 Kazusaka, A., 1227, 2635 Kemball, C., 3069 Kerr, C W., 85 Kido, K., 3139 Kiennemann, A., 21 19 King, D. A,, 1966,2001, 2079, Kinnaird, S., 3399 Kinoshita, N., 2765 Kira, A., 1539 Kiricsi, I., 1109 Kitagawa, H., 2913 Kitaguchi, K., 1395 Kiwi, J., 1101 Klein, J., 1703 Klinszporn, L., 2261 Klofutar, C., 231 1 Knoche, W., 2847 Knozinger, H., 2088, 2171 Kobayashi, J., 1395 Kobayashi, M., 721 Koda, S., 527 Kondo, Y., 1089 Konishi, Y., 721 Koopmans, H.J. A., 1485 Kordulis, C., 627 Korf, S. J., 1485 Koutsoukos, P. G., 1477 Kowalak, S., 535 Krell, M., 3419 Kristyan, S., 2825 Kubelkova, L., 511 Kubokawa, Y., 675, 1761 Kumamaru, T., 1641 Kuroda, K., 1851 Kusabayashi, S., 1089 Kuzuya, M., 1579 La Ginestra, A., 853 Lackey, D., 2001 tajtar, L., 1405 Lambelet, P., 141 Lambert, R. M., 1963, 1964, 2035, 2082, 2083, 2084 Lamotte, J., 1417 Lang, N. D., 1935 Larher, Y., 3355 Laschi, F., 1731 Laurin, M., 2119 Lauter, H. J., 3199 Lavagnino, S., 477 Lavalley, J-C., 1417 Lawin, P.B., 1169 Lawrence, C., 2331 Lawrence, S., 1347 Le Bras, M., 1711 Leach, H. F., 3069 Leaist, D. G., 829 Lecomte, C., 177 Lee, E. F. T., 1531 Leeper, J. D., 3229 Lefferts, L., 3161 2080, 2081 Korth, H-G., 95 Lengeler, B., 2157 Lercher, J. A., 2080, 2255 Leroy, J-M., 1711 Letellier, P., 1725 Levin, M. E., 2061 Lijour, Y., 3283, 3295 Lima, M. C. P., 2705 Lin, C. P., 13 Lin, Y-J., 2091 Linares-Solano, A., 1081 Lincoln, S. F., 2459, 2697, 2751, Lindgren, M., 893, 1815 Lippens, B. C., 1485 Littrell, D. M., 3271 Liu, R-L., 635 Liu, T., 1063 Liu, Y., 2993 Liwu, L., 2573 Loliger, J., 141 Lorenzelli, V., 853, 1591 Loretto, M. H., 615 Lougnot, D. J., 2935 Lucassen, J., 3093 Luckham, P. F., 1703 Lund, A., 893, 1815, 1869 Luo, H., 2103 Lycourghiotis, A., 627, 1179 Lynch, J., 1417 Lyons, C.J., 645 Lyons, M. E. G., 299 Machin, W. D., 1203, 2709, Makkowiak, M., 2541 MacLaren, J. M., 1945, 1965 Maestre, A., 1029 Maezawa, A., 665 Makela, R., 51 Manfredi, M., 1609 Maniero, A. L., 57, 69 Manzatti, W., 2213 Marchese, L., 477 Marcus, Y., 339, 2985 Mari, C. M., 705 Markarian, S. A., 1189 Martin Luengo, M. A., 1347, Martin-Martinez, J. M., 1081 Mashkovsky, A. A., 1879 Masiakowski, J. T., 893, 1869 Masliyah, J. H., 547 Matralis, H., 1179 Matsuda, T., 3107 Matsuura, H., 789 Maurice, Y., 3355 Maxwell, I. A., 1449 McAleer, J. F., 1323 McCarthy, S. J., 657 McDonald, J. A., 1007 McLauchlan, K. A., 29 Mead, J., 2347 Mehandru, S. P., 463 Mehnert, R., 2365 Mehta, G., 2467 Meriadeau, P., 2140 ( 4 3237 2719 1651 MCriaudeau, P., 21 13 Merwin, L.H., 1055 Micic, 0. I., 1127 Mijin, A,, 2605 Mills, A., 2317, 2331, 2647 Mintchev, L., 2213 Miura, H., 3107 Miyahara, K., 1227 Miyamoto, A., 3303 Miyata, H., 675, 1761, 1851 Mochida, I., 1427 Molina-Sabio, M., 1081 Monk, C. B., 425 Montagne, X., 1417 Morazzoni, F., 705, 2271 Mori, K., 3303 Morimoto, T., 943, 957 Moriyama, T., 3139 Morris, J. J., 2867 Moseley, P. T., 1323 Mosseri, S., 3001 Mostowicz, R., 3459 Moyer, J. W., 3229 Moyes, R. B., 905 Mozzanega, M-N., 697 Muller, A., 2157 Muiioz, M. A., 1029 Murakami, Y., 3303 Nabiullin, A. A., 1879 Naccache, C., 2113 Nagao, M., 1739 Nagaoka, T., 1823 Nair, V., 487 Naito, S., 2475 Nakai, S., 1579 Nakajima, T., 1315 Nakamura, D., 3207 Nakata, M., 2449 Napper, D. H., 1449 Narayanan, S., 733 Narducci, D., 705 Nath, J., 3167 Nayak, R.C., 1307 Naylor, G. R. S., 3447 Nazer, A. F. M., 1119 Nebuka, K., 2605 Nedeljkovic, J. M., 1127 Nenadovic, M. T., 1127 Neta, P., 3001 Niccolai, N., 1731 Niemann, W., 2157 Nishida, S., 1795 Nogaj, B., 2541 Nomura, H., 527 Nomura, M., 1227, 1779, 2635 Nonaka, K., 3317 Norris, J. 0. W., 1323 Norris, J. R., 13 Nnrrskov, J. K., 1935 Notheisz, F., 2359 Nukui, K., 743 Nuttall, S., 559 O’Brien, A. B., 371 Ochoa, J. R., 2289 Odinokov, S. E., 1879Ogura, K., 1823 Ohlmann, G., 31 15 Ohno, M., 1559 Ohno, T., 675 Ohshima, K., 789 Okabayashi, H., 789 Okada, T., 3317 Okamoto, Y., 665 Okubo, T., 2487, 2497 Okuda, T., 1579 Okuhara, T., 1213 Olofsson, G., 3331 O’Malley, P. J. R., 2227 Onishi, T., 2765, 3139 Ono, T., 675, 1761 Ono, Y., 2913 Otsuka, K., 1315 Ott, J.B., 1553 Oyama, K., 3189 Page, F., 2641 Paljk, S., 231 1 Pallas, N. R., 585 Parry, D. J., 77 Parsons, B. J., 3415 Patel, I., 2317, 2331 Patel, J. S., 3429 Patel, K. B., 3177 Patil, K., 2467 Patrono, P., 853 Peden, C. H. F., 1967 Pedersen, E., 2157 Pedersen, J. A., 107 Pedulli, G. F., 91 Penar, J., 1405 Pendry, J. B., 1945 Penfold, J., 2773 Perez-Tejeda, P., 1029 Pethica, B. A., 585 Pethrick, R. A., 938 Pfeifer, H., 2301, 3459 Pichat, P., 697 Pielaszek, J., 1293 Pilarczyk, M., 281, 2261 Pilz, W., 2301 Pizzini, S., 705 Pletcher, D., 2787, 2795 Poels, E. K., 2140 Pogni, R., 151 Pomonis, P., 627 Pomonis, P. J., 1363 Ponec, V., 1964, 1965, 2071, 2072, 2074, 2083, 2103, 2136, 2138, 2139, 2244, 2251 Price, C., 3224 Primet, M., 1469 Prins, R., 2087, 2136, 2137, 2145, 2169, 2170, 2172 Priolisi O., , 57 Pritchard, J., 1963, 2085, Prugnola, A., 1731 Puchalska, D., 1253 Purushotham, V., 21 1 Radulovic, S., 559 Raffi, J.J., 225 2249 AUTHOR INDEX Rajaram, R. R., 2130 Ramaraj, R., 1539 Ramirez, F., 2279 Ramis, G., 1591 Rees, L. V. C., 1531, 1843 Renouprez, A., 3199 Renyuan, T., 2573 Resasco, D. E., 2091 Reyes, P. N., 1347 Richards, D. G., 2138 Richoux, M-C., 3001 Richter-Mendau, J., 1843 Riley, B. W., 2140, 2253 Ritschl, F., 1041 Riva, A., 2213 Riviere, J. C., 351 Roberts, M. W., 351, 2047, Robinson, B. H., 985, 1007, Rodriguez, R. M., 2813 Rodriguez-Izquierdo, J. M., Rodriguez-Reinoso, F., 1081 Rollins, K., 1347 Roman, V., 177 Romiio, M. J., 43 Rooney, J. J., 2077, 2080, 2086, Ross, J. R. H., 3161 Rosseinsky, D. R., 231, 245 Rossi, C., 1731 Rowlands, C.C., 43, 135 Rubio, R. G., 819 Rudham, R., 1631, 3223 Sabbadini, M. G. C., 2271 Sakai, K., 2895 Sakai, T., 743, 1823 Sakakini, B., 1975 Sakata, Y., 2765 Sakurai, M., 2449 Salazar, F. F., 2663 Saleh, J. M., 2391 Salmeron, M., 2061 Salmon, T. M. F., 2421, 2433 Sanchez, M., 1029 Sanfilippo, D., 2213 Sangster, D. F., 657 Saraby-Reintjes, A., 271 Sato, K., 3061 Sato, T., 1559 Saucy, F., 141 Saumagne, P., 3283, 3295 Savoy, M-C., 141 Sayed, M. B., 1149, 1751, 1771 Schiller, R. L., 3237 Scholten, J. J. F., 1966, 2073, 2246, 2255, 2257 Schuller, B., 2103 Seebode, J., 1109 Segal, M. G., 371 Segre, U., 69 Self, V. A., 2693 Sendoda, Y., 2913 (vii) 2084, 2085, 2086, 2248, 3225 2407 2279 2089 Schulz-Ekloff, G., 3015 Sermon, P. A., 1347, 1369, 1651, 1667, 2175, 2243, 2256, 2693 Seyedmonir, S., 813 Shelimov, B.N., 2381 Sheppard, N., 1966, 2075 Shibata, Y., 3107 Sidahmed, I. M., 439 Simonian, L. K., 1189 Singh, G., 3167 Smith, B. V., 2705 Smith, D. H., 1381 Smith, G. V., 2359 Smith, J. R. L., 2421, 2433 Soderman, O., 1515 Sokolowski, S., 1405 Solymosi, F., 2015, 2074, 2078, 2081, 2082, 2086, 2137, 2142, 2247 Somorjai, G. A., 2061 Sorrie, G. A., 3345 Spencer, M. S., 2193, 2245, Srivastava, R. D., 3229 Staples, E., 2773 Steenken, S., 113 Stevens, D. G., 29 Stevenson, S., 2175 Stone, F. S., 1237, 2080, 2084, Stratford, M. R. L., 3177 Strumulo, D., 2271 Stuckey, M., 2525 Su, Z., 2573 Suda, Y., 1739 Suematsu, H., 2605 Sugahara, Y., 1851 Sugiyama, K., 3107 Suppan, P., 495 Sustmann, R., 95 Suzuki, T., 1213 Svetlitid, V., 1169 Swartz, H.M., 191 Swift, A. J., 1975 Symons, M. C. R., 1, 383, 759, 2803, 3419 Szafran, M., 2541 Szostak, R., 487 Tabner, B. J., 167 Taga, K., 789 Takahashi, N., 2605 Takaishi, T., 411, 2681, 3317 Tamagawa, H., 3189 Tan, W. K., 645 Tanaka, H., 1395, 3189 Tanaka, K., 1213, 1779, 1859 Tanaka, K-i., 1859 Tanimoto, M., 2475 Tannakone, K., 2553 Tascon, J. M. D., 3149 Tassi, L., 3129 Tatarchuk, B. J., 3271 Taylor, P. J., 2867 Tejuca, L. G., 3149 Tempere, J.-F., 1137 Tempest, P. A., 925 2246, 2247, 2248, 2249, 2250 2254AUTHOR INDEX Theocharis, C. R., 1601, 2835 Thikry, C. L., 225 Thomas, T. L., 487 Thomson, S. J., 1893, 1964, 1965, 2083 Thurai, M., 841 Tiddy, G. J. T., 2735 Tilquin, B., 125 Timmons, R. B., 2825 Tkaczyk, M., 3083 Tomellini, M., 289 Tonge, J.S., 231, 245 Toprakcioglu, C., I703 Topsse, H., 2157, 2169, 2171 Topsse, N-Y., 2157 Torregrosa, R., 1081 Tosi, G., 3129 Toyoshima, I., 1213 Trabalzini, L., 151 Trifiro, F., 2213, 2246, 2251, Tsuchiya, S., 743 Tsuiki, H., 1395, 3189 Tsukamoto, K., 789 Turner, J. C. R., 937 Tyler, J. W., 925, 1355 Ueno, A., 1395, 3189 Ukisu, Y., 1227, 2635 Uma, K., 733 Unwin, P. R., 1261 Vaccari, A., 2213 Vachon, A., 177 van de Ven, T. G. M., 547 van den Boogert, J., 2103 van der Lee, G., 2103 2254 van der Riet, M., 2963 van Ommen, J. G., 3161 van Santen, R. A., 1915, 1963, 1964, 2077, 2140, 2250 Varani, G., 1609 Vattis, D., 1179 Vickerman, J. C., 1975, 2075 Villani, R. P., 2751 Vincent, P. B., 225 Vink, H., 801, 941 Vissers, J. P. R., 2145 Vong, M. S. W., 1369, 1667 Vordonis, L., 627 Vuolle, M., 51 Vvedensky, D.D., 1945 Waddicor, J. I., 751 Waddington, D. J., 2421, 2433 Waghorne, W. E., 2585 Waller, A. M., 1261 Wang, E., 2993 Wang, Z-C., 3367 Waters, D. N., 1601 Waugh, K. C., 2193, 3223 Webb, G., 3399 Wells, C. F., 439, 939, 11 19, Wells, P. B., 905 Whalley, E., 2901 Whan, D. A., 2193 White, A., 2459 White, J. W., 3447 White, L. R., 591, 873 Whyman, R., 905 Wickramanayake, S., 2553 Williams, D. E., 1323 1281 Williams, G., 2647 Williams, J. O., 323 Williams, R. J. P., 1885 Williams, W. J., 371 Wilson, H. R., 1885 Wilson, 1. R., 645, 657 Winstanley, D., 1835 Wbjcik, D., 1253 Wurie, A. T., 1651 Wyatt, J. L., 2803 Wyn-Jones, E., 2525, 2735 Xyla, A. G., 1477 Yamada, K., 743, 3107 Yamaguchi, T., 3189 Yamamoto, H., 3207 Yamamoto, Y., 1641, 1795 Yamasaki, S., 1641 Yamashita, H., 2883, 2895 Yanagihara, Y., 1579 Yanai, Y., 1641 Yangbo, F., 2533 Yanv, S., 1685 Yonezawa, Y., 1559 Yoshida, S., 2883, 2895 Yoshikawa, M., 2883 Yoshino, T., 1823 Yun, D.L., 2251 Zaki, M. I., 1601, 2835 Zhang, Q., 635 Zibrowius, B., 3459 Zikanova, A., 2301 Zsigmond, A. G., 2359 Zukal, A., 3015 (viii)THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM No. 23 Molecular Vibrations University of Reading, 15-16 December 1987 Organising Committee: Professor I. M. Mills (Chairman) Dr J. E. Baggott Professor A. D. Buckingham Dr M. S. Child Dr N. C. Handy Dr B. J. Howard The Symposium will focus on recent advances in our understanding of the vibrations of polyatomic molecules. The topics to be discussed will include force field determinations by both ab initiu and experimental methods, anharmonic effects in overtone spectroscopy, local modes and anharmonic resonances, intramolecular vibrational relaxation, and the frontier with molecular dynamics and reaction kinetics.The programme and application form may be obtained from: Mrs. Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION No. 8 5 Solvation University of Durham, 28-30 March 1988 Organising Committee: Professor M. C. R. Symons (Chairman) Professor J. S. Rowlinson Professor A. K. Covington Dr I. R. McDonald Dr J. Yarwood Dr A. D. Pethybridge Professor W. A. P. Luck Dr D. A. Young The purpose of the Discussion is to compare solvation of ionic and non-ionicspecies in the gas phase and in matrices with corresponding solvation in the bulk liquid phase.The aim will be to confront theory with experiment and to considerthe application of these concepts to relaxation and solvolytic processes. Topics to be covered are: clusters, (c) Gas phase ionic clusters, (d) Liquid phase ionic solutions, (e) Dynamic processes including solvolysis. (a) Gas phase non-ionic clusters, (b) Liquid phase non-ionic Speakers include: H. L. Friedman, B. J. Howard, M. J. Henchman, S. Tomoda, 0. Kajimoto, M. H. Abraham, Yu Ya Efimov, J. L. Finney, P. Suppan, J. P. Devlin, D. W. James, G. W. Neilson, T. Clark, M. L. Klein, J. T. Hynes, G. A. Kenney-Wallace, G. R. Fleming, M. J. Blandamer and D. Chandler. The preliminary programme may be obtained from: Mr.Y. A. Fish, The Royal Society of Chemistry, Burlington House, London WlV OBN.THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION No. 86 Spectroscopy at Low Temperatures University of Exeter, 13-15 September 1988 Organising Committee: Professor A. C. Legon (Chairman) Dr P. B. Davies Dr B. J. Howard Dr P. R. R. Langridge-Smith Dr R. N. Perutz Dr M. Poliakoff The Discussion will focus on recent developments in spectroscopy of transient species (ions, radicals, clusters and complexes) in matrices or free jet expansions. The aim of the meeting is to bring together scientists interested in similar problems but viewed from the perspective of different environments. Further information may be obtained from: Professor A.C. Legon, Department of Chemistry, University of Exeter, Exeter EX4 4QD. THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY WITH THE ASSOClAZlONE ITALIANA DI CHIMICA FISICA, DIVISION DE CHlMlE PHYSIQUE OF THE SOCIETE FRANCAISE DE CHlMlE AND DEUTSCHE JOINT MEETING BUNSEN GESELLSCHAFT FUR PHYSIKALISCHE CHEMIE Structure and Reactivity of SurFaces Centro Congressi, Trieste, Italy, 13-16 September 1988 Organising Committee: M. Che V. Ponec F. S. Stone G. Ertl R. Rosei A. Zecchina The conference will cover surface reactivity and characterization by physical methods: (i) Metals (both in single crystal and dispersed form) (ii) Insulators and semiconductors (oxides, sulphides, halides, both in single crystal and dispersed forms) (iii) Mixed systems (with special emphasis on metal-support interaction) The meeting aims to stimulate the comparison between the surface properties of dispersed and supported solids and the properties of single crystals, as well as the comparison and the joint use of chemical and physical methods.Further information may be obtained from: Professor C. Morterra, lnstituto di Chimica Fisica, Corso Massimo D’Azeglio 48, 10125 Torino, Italy.THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY SYMPOSIUM Orientation and Polarization Effects in Reactive Collisions To be held at the Physikrentrum, Bad Honnef, West Germany, 12-14 December 1988 Organising Committee: Dr S. Stoke Professor R. N. Dixon Professor J. P. Simons Dr K. Burnett Professor H. Loesch Professor R. A. Levine The Symposium will focus on the study of vector properties in reaction dynamics and photodissociation rather than the more traditional scalar quantities such as energy disposal, integral cross-sections and branching ratios.Experimental and theoretical advances have now reached the stage where studies of Dynamical Stereochemistry can begin to map the anisotropy of chemical interactions. The Symposium will provide an impetus to the development of 3-D theories of reaction dynamics and assess the quality and scope of the experiments that are providing this impetus. Contributions for consideration by the Organising Committee are invited in the following areas: (A) Collisions of oriented or rotationally aligned molecular reagents (B) Collisions of orbitally aligned atomic reagents (C) Photoinitiated ‘collisions‘ in van der Waals complexes (D) Polarisation of the products of full and half-collisional processes Abstracts of about 300 words should be sent by 31 October 1987 to: Professor J.P. Simons, Department of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD Full papers for publication in the Symposium volume will be required by 15 August 1988. THE FARADAY DIVISION OF THE ROYAL SOCIETY OF CHEMISTRY GENERAL DISCUSSION No. 87 Catalysis by Well Characterised Materials University of Liverpool, 11-13 April 1988 Organising Committee: Professor R. W. Joyner (Chairman) Professor A. K. Cheetham Professor F. S. Stone The understanding of heterogeneous catalysis is an important academic activity, which compliments industry’s continuing search for novel and more efficient catalytic processes.The emergence of relevant, in particular in situ techniques and new developments of well established experimental approaches to catalyst characterisation are making a very significant impact on our knowledge of catalyst composition, structure, morphology and their inter-relationships. Well characterised catalysts, which will be the subject of the Faraday Discussion, include single-crystal surfaces, whether of metals, oxides or sulphides; crystalline microporous solids, such as zeolites and clays, and appropriate industrial catalysts. The elucidation of structure/function relationships and catalytic mechanism will be important aspects of the scientific programme. Contributions describing novel methods for synthesising well characterised catalysts and also reporting important advances in characterisation techniques will also be welcome.Contributions for consideration by the Organising Committee are invited and abstracts of about 300 words should be sent by 31 May 1988 to: Professor R. W. Joyner, Leverhulme Centre for Innovative Catalysis, Department of Inorganic, Physical and Industrial Chemistry, University of Liverpool, Grove Street, P. 0. Box 147, Liverpool L69 3BX. Full papers for publication in the Discussion volume will be required by December 1988. Dr. K. C. Waugh Professor P. B. WellsFARADAY DIVISION INFORMAL AND GROUP MEETINGS Electrochemistry Group with the Society of Chemical Jndustry Batteries To be held at the Society of Chemical Industry, London on 13 October 1987 Further information from Dr S.P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB Polymer Ph ysics Group with the Institute of Marine Engineers Polymers in a Marine Environment To be held in London on 14-16 October 1987 Further information from Professor G. J. Lake, MRPRA, Brickendonbury, Herts SG13 8NL Division London Symposium: Kinetics and Spectroscopy of Alkali and Ionic Species in the Laboratory in Flames and in the Upper Atmosphere To be held at the Scientific Societies Lecture Theatre, London on 3 November 1987 Further information from Mrs Y. A. Fish, The Royal Society of Chemistry, Burlington House, London W1V OBN Division with the Institute of Ph ysics and the British Society for Electro Heat Seminar in Drying and Curing To be held at Boddington Hall, University of Leeds on 17 November 1987 Further information from the Meetings Officer, Institute of Physics, 47 Belgrave Square, London SWlX 8QX Electrochemistry Group with the Electroanalytical Group Chemical Sensors To be held in London on 9-10 December 1987 Further information from Dr S.P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB Electrochemistry Group with the Society of Chemical lndustry Electrosynthesis To be held at the University of York on 15-17 December 1987 Further information from Dr S. P. Tyfield. Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB Colloid and Interface Science Group with the Society of Chemical Jndustry The Preparation of Colloid Particulates and the Annual General Meeting To be held at the Society of Chemical Industry, Belgrave Square, London on 16 December 1987 Further information from Dr R.Buscall, ICI plc, Corporate Colloid Laboratory, PO Box 11, The Heath, Runcorn, Cheshire WA7 4QE High Resolution Spectroscopy Group with CCP6 Spectroscopy and Dynamics of highly Excited States of Molecules To be held at the University of Reading on 16-18 December 1987 Further information from Professor I. M. Mills, Department of Chemistry, University of Reading, Whiteknights, Reading RG6 2AD Neutron Scattering Group Scattering from Disordered Systems To be held at the University of Bristol on 16-18 December 1987 Further information from Dr G.W. Neilson. H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL Electrochemistry Group Electrochemistry/Surface Science: Must the Relationship remain Platonic? To be held at the University of Southampton on 6-7 January 1988 Further information from Dr S. P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB (xii)Electrochemistry Group Workshop on Electrochemical Techniques and Instruments To be held at the University of Warwick on 6-7 January 1988 Further information from Dr P. N. Bartlett, Department of Chemistry, University of Warwick, Coventry CV4 7AL Surface Reactivity and Catalysis Group with the Process Technology Group and the Institute of Chemical Engineers Opportunities for Innovation in the Application of Catalysis To be held at Queen Mary College, London on 6-7 January 1988 Further information from Professor J.Pritchard, Queen Mary College, London Division with the Institute of Mathematics and its Applications Mathematical Modelling of Semiconductor Devices and Processes To be held at the University of Loughborough on 7-8 January 1988 Further information from the Institute of Mathematics, Maitland House, Warrior Square, Southend-on-Sea SS1 2JY Division London Symposium: Modern Electrochemical Systems To be held at Imperial College, London on 12 January 1988 Further information from Mrs Y. A. Fish, Royal Society of Chemistry, Burlington House, London W1V OBN Polymer Physics Group with the 3Ps Group Plastics, Packaging and Printing To be held at the Institute of Physics, 47 Belgrave Square, London on 18 February 1988 Further information from Dr M.Richardson, National Physical Laboratory, Teddington, Middlesex l w 1 1 OLW Theoretical Chemistry Group Postgraduate Students’ Meeting To be held at University College, London on 2 March 1988 Further information from Dr G. Doggett, Department of Chemistry, University of York, York Colloid and Interface Science Group with The Society of Chemical Industry and British Radio frequency Spectroscopy Group Spectroscopy in Colloid Science To be held at the University of Bristol on 5-7 April 1988 Further information from Dr R. Buscall, ICI Corporate Colloid Science Group, PO Box 11, The Heath, Runcorn WA7 40E Annual Congress: Division with Electrochemistry Group Solid State Materials in Electrochemistry To be held at the University of Kent, Canterbury on 12-15 April 1988 Further information from Dr J.F. Gibson, Royal Society of Chemistry, Burlington House, London W1V OBN Electrochemistry Group with The Society of Chemical Industry Electrolytic Bubbles To be held at Imperial College, London on 31 May 1988 Further information from Professor W. J. Albery, Department of Chemistry, Imperial College of Science and Technology, South Kensington, London SW7 2AY Electrochemistry Group with The Society of Chemical Industry Chlorine Symposium To be held at the Tara Hotel, London on 1-3 June 1988 Further information from Dr S. P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GLI 3 9BP Gas Kinetics Group Xth International Symposium on Gas Kinetics To be held at University College, Swansea on 24-29 July 1988 Further information from Dr G.Hancock, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 302 (xiii)Electrochemistry Group Workshop on Electrochemical Techniques and Instruments To be held at the University of Warwick on 6-7 January 1988 Further information from Dr P. N. Bartlett, Department of Chemistry, University of Warwick, Coventry CV4 7AL Surface Reactivity and Catalysis Group with the Process Technology Group and the Institute of Chemical Engineers Opportunities for Innovation in the Application of Catalysis To be held at Queen Mary College, London on 6-7 January 1988 Further information from Professor J. Pritchard, Queen Mary College, London Division with the Institute of Mathematics and its Applications Mathematical Modelling of Semiconductor Devices and Processes To be held at the University of Loughborough on 7-8 January 1988 Further information from the Institute of Mathematics, Maitland House, Warrior Square, Southend-on-Sea SS1 2JY Division London Symposium: Modern Electrochemical Systems To be held at Imperial College, London on 12 January 1988 Further information from Mrs Y.A. Fish, Royal Society of Chemistry, Burlington House, London W1V OBN Polymer Physics Group with the 3Ps Group Plastics, Packaging and Printing To be held at the Institute of Physics, 47 Belgrave Square, London on 18 February 1988 Further information from Dr M. Richardson, National Physical Laboratory, Teddington, Middlesex l w 1 1 OLW Theoretical Chemistry Group Postgraduate Students’ Meeting To be held at University College, London on 2 March 1988 Further information from Dr G. Doggett, Department of Chemistry, University of York, York Colloid and Interface Science Group with The Society of Chemical Industry and British Radio frequency Spectroscopy Group Spectroscopy in Colloid Science To be held at the University of Bristol on 5-7 April 1988 Further information from Dr R. Buscall, ICI Corporate Colloid Science Group, PO Box 11, The Heath, Runcorn WA7 40E Annual Congress: Division with Electrochemistry Group Solid State Materials in Electrochemistry To be held at the University of Kent, Canterbury on 12-15 April 1988 Further information from Dr J. F. Gibson, Royal Society of Chemistry, Burlington House, London W1V OBN Electrochemistry Group with The Society of Chemical Industry Electrolytic Bubbles To be held at Imperial College, London on 31 May 1988 Further information from Professor W. J. Albery, Department of Chemistry, Imperial College of Science and Technology, South Kensington, London SW7 2AY Electrochemistry Group with The Society of Chemical Industry Chlorine Symposium To be held at the Tara Hotel, London on 1-3 June 1988 Further information from Dr S. P. Tyfield, Central Electricity Generating Board, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GLI 3 9BP Gas Kinetics Group Xth International Symposium on Gas Kinetics To be held at University College, Swansea on 24-29 July 1988 Further information from Dr G. Hancock, Physical Chemistry Laboratory, South Parks Road, Oxford OX1 302 (xiii)

ISSN:0300-9599    

DOI:10.1039/F198783BP147

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I , 1987,83 (ll), 3229-3236 Effusion Mass Spectrometric Determination of Thermodynamic Properties of the Gaseous Mono- and Di-hydroxides of Calcium and KCaO(g) Milton Farber" and Rameshwar D. Srivastava Space Sciences, Inc., 135 W. Maple Aue., Monrovia, California 91016, U.S.A. James W. Moyer and John D. Leeper Southern California Edison Company, Rosemead, California, U.S.A . Effusion mass spectrometric measurements were made to obtain thermo- dynamic data for the gaseous mono- and di-hydroxides of calcium. An investigation of the reaction CaO(c) ++H,(g) = CaOH(g) in the temperature range 1720-1983 K led to third and second law AGg8 values of 444.3 f 4 kJ mol-l and 443.1 f 16 kJ m o P , respectively. The corresponding values for CaOH(g) were - 190.8 f 8 kJ mol-l and - 192.0 f 16 kJ mol-l.The third law Do for Ca-OH was 404.2 f 8 kJ mol-l. Two reactions were employed for obtaining thermal data for Ca(OH),(g) CaOW + H,O(g) = Ca(OH),(g) 2CaOH(g) = Ca(g) + Ca(OH),(g) in the temperature range 1720-1900 K. Third- and second-law values for the AGzg8 of Ca(OH),(g) obtained from these reactions were - 605.8 f 8 kJ mol-l and - 602.5 f 20 kJ mol-l, respectively. The third-law Do for Ca+ 20H was 854.8 8 kJ mol-l. A knowledge of the K reactions with the mineral matter ingredients in the combustion products of coal is necessary for obtaining definitive electrical conductivities for design of coal-fired electric power plants. Thermodynamic data were obtained for KCaO(g) species from the reaction in the temperature range 180&1950 K, and the isomolecular reaction CaOH(g) + K(g) = KCaO(g) + iH,(g) in the temperature range 1880-1950 K.A third-law heat of reaction of - 21 5.1 f 16 kJ mol-l led to a third-law AGZg8 of - 328.0 f 20 kJ mol-l for KCaO(g). The coal-fired open-cycle magnetohydrodynamic (MHD) power plant involving seeding of the combustion products (plasma) with small amounts of potassium salts (1-1.5%) is one of several methods being studied as a promising source of electric power for future energy requirements. The electrical power is derived from the increased plasma conductivity resulting from the free electrons produced by ionization of the potassium at the high combustion temperature. Typically, coal contains ca. 10% organic mineral matter of which over 50% is aluminium and silicon oxides, The concentration of calcium compounds, mainly CaO, is third in magnitude after aluminum and silicon in the mineral matter of coal.When utilizing this coal in an open-cycle MHD system, these oxides may react with the potassium seed affecting channel performance and seed recovery. Therefore, it is highly 3229 107-23230 Eflusion Mass Spectrometry beneficial to identify nearly all possible reactions involving potassium with the high- temperature combustion gases and slag products. The two laboratories from which this manuscript is submitted cooperated in a joint effort to investigate the stability and other thermodynamic properties of the various K-containing compounds. They have previously reported results of studies concerning the species formed between K and 0, and H2,1 K and S,, K-Al-0,3 and K-Si-0 and K-B-0.4 This paper reports on the reactions leading to thermodynamic properties of CaOH(g), Ca(OH),(g) and KCaO(g).Thermodynamic data leading to bond energies for CaOH(g) and Ca(OH),(g) have previously been reported from flame st~dies.~-’O None have been published for KCaO(g). Experimental The dual vacuum chamber-quadrupole mass spectrometer used in these experiments has been described previously.ll The experiments to obtain thermodynamic data for the mono-and di-hydroxides of calcium included a metered flow system to provide a constant pressure of hydrogen or water vapour over the calcium oxide contained within the alumina effusion cell. The experiments for obtaining AHf for KCaO(g) included the ‘triple boiler’ technique in which hydrogen metered at ambient conditions flowed into the effusion cell through one of two effusion tubes connected to the effusion cell.The other tube was wrapped in nichrome wire and connected to an alumina reservoir, also heated by nichrome wire, containing potassium iodide. The temperature control of this reservoir allowed a constant partial pressure of KI(g) to flow into the effusion cell. An alumina effusion cell 25 mm long, with an inside diameter of 6.8 mm and having an elongated orifice 0.75 mm diameter by 5.5 mm long for beam collimation, was employed. The ion intensities were identified by their masses, isotopic distributions and appear- ance potentials. The method of determining the mass spectrometer resolution, as well as the measurement of isotopic-abundance ratios, has been presented previously.12 All quadrupole experimental mass discrimination effects were taken into account and necessary corrections to ion intensity pressure relations were made.Only the chopped, or shutterable, portion of the intensities was recorded, since the mass spectrometer was equipped with a beam modulator and a phase-sensitive amplifier. Ion currents, which originated from species in the molecular beam, appeared as a 30 Hz square-wave, while background gases continued to exist as a d.c. current where an a.c. current could be observed in a d.c. signal 1000 times greater. To obtain the bond energies and the enthalpies of formation it was necessary to ascertain with a high degree of confidence that the measured ion intensities were those from parent species and not from the fragments of the larger molecules.Therefore, the mass spectrometer was operated at an ionizing potential 1-2 V above the appearance potential, which, in nearly all cases, allows only the formation of the ion from the parent species since a fragmentation process usually occurs at higher ionization potentials. 13-17 Elemental silver and gold were used for intensity conversion to partial pressure calibrations. The metered H, and H,O(g) flows were converted to partial pressures via the Knudsen equation : ti KAt pmm = 17.4 - d( T / M ) where G is the weight loss in g, t is the time in s, A is the orifice area in cm2, T is the absolute temperature in K, M is the molecular weight and K is Clausing’s factor, a function of orifice length/orifice radius.The appearance potentials for the relevant ionic species are listed in table 1 . For theM . Farber, R. D. Srivastava, J . W. Moyer and J . D. Leeper Table 1. Ionization potentials and ionization cross-sections ionization ionization cross-section potential (estimated) (all & l)/eV / cm2 Ca 0 H H2 CaO CaOH Ca(OW2 KCaO K 6.0 13.6 13.5 15.5 6.5 6.0 9.0 10.0 4.5 7.05 1.31 0.234 0.327 5.852 4.260 2.890 9.50 7.67 323 1 reactions, ion intensities corrections were made for the differences in relative cross- sections and their molecular masses. The relative maximum ionization cross-sections were taken from Mann. la Those for the molecular species were calculated by multiplying the sum of atomic cross-sections by an empirical factor of O.7.lgp2l These values are probably accurate to 30% and for isomolecular reactions would possibly yield errors of +4 kJ mol-1 in the third-law values.Owing to the uncertainties in these cross-section estimates, it is advisable to have second-law corroboration for definitive thermodynamic values. Corrections were made for the electron-multiplier corrections, y , and applied to the individual species intensities, e.g. Methods of calculation to obtain second- and third-law thermodynamic quantities have been presented previously. 1 3 9 l9 The calculated cross-sections, o, for the ionic species are given in table 1. Results Heat of Formation of CaOH(g) The reaction CaO(c) +4H,(g) = CaOH(g) ( 3 ) was employed to obtain data leading to a value for the of CaOH(g).This reaction was studied in the temperature range 1720-1983 K as described in the Experimental section. Ion intensities were obtained for the gaseous species H, and CaOH. The H, was metered at a flow rate equivalent to a partial pressure of 1.1 x lop4 atmt at 298 K. The ion intensities for CaOH were converted to partial pressures employing gold via eqn (1). The ion intensities were corrected for cross-section and multiplier effects. The partial pressures for the equilibrium constant and AH values for reaction (3) are listed in table 2. Thermal functions for the species involved were taken from the JANAF Tables.,, t 1 atm = 101325 Pa.3232 Eflusion Mass Spectrometry Table 2. Thermodynamic data for pHz, pCeOH and A g Q 8 for the reaction CaO(c) + iH,(g) = CaOH(g) partial pressures (atm) - A[(Go - %98)/ ' G 9 8 T/K PHz PCaOH log k, /J mol-l K-l /kJ mol-l 1720 2.68 x lov4 9.08 x 10-lo 1750 2.70 x 1.36 x 1800 2.74 x 2.75 x 1825 2.76 x 4.60 x 1850 2.78 x 7.39 x 1880 2.80 x lop4 1.1 1 x 1900 2.81 x 1.48 x 1925 2.83 x 1.86 x 1953 2.85 x 3.00 x 1983 2.87 x lob4 4.70 x - 7.26 - 7.08 - 6.78 - 6.56 - 6.35 -6.18 - 6.05 - 5.95 - 5.75 - 5.56 205.1 208.2 213.5 216.1 219.2 224.7 224.1 226.7 229.6 234.0 443.5 444.7 446.4 444.7 443.5 443.9 443.9 445.6 444.3 444.3 average 444.3 & 4 - 5.5 h .: -6.0 1 + v 4 M ' -6.5 -7.0 0.1 0 -0.1 -0.2 5.0 5.2 5.4 5.6 5.8 104 KIT Fig.1. Plot of the logarithm of equilibrium KI based on the relative intensities against the reciprocal of the absolute temperature for reactions (a) 3, (b) 5 and (c) 7.The third-law A z g 8 average value for reaction (3) was 444.3 _+4 kJ mol-l. Employing a A%,,, value of -635.1 kO.8 kJ mol-1 for CaO(c),22 a of - 190.8f 8 kJ rno1-l was calculated for CaOH(g), with a third-law D,(Ca-OH) value of 404.2 f 8 kJ mol-l. A van't Hoff plot of logK, us. 1/T from the uncorrected intensity data (fig. 1) ledM . Farber, R. D. Srivastava, J. W. Moyer and J . D . Leeper 3233 Table 3. Thermodynamic data for pHpO, pCa(OH)e and AH& for the reaction C a w + H2O(g) = Ca(OH)2(g) 1800 8.21 x 1.01 x -4.91 102.6 271.5 1820 8.26 x 1.54 x -4.73 103.7 268.2 1860 8.35 x 1.81 x -4.66 105.9 271.5 1880 8.39 x 2.80 x -4.60 106.9 272.4 1900 8.44 x 10-4 2.63 x -4.51 108.0 271.5 1920 8.48 x 3.16 x -4.43 109.0 271.5 1950 8.55 x 4.26 x -4.30 110.6 271.1 average 2 17.1 f 4 Table 4.Thermodynamic data for pca, pCaOH, pCa(OH)p and AGg8 for the reaction 2CaO(g) = Ca(g) + Ca(OH),(g) partial pressures (atm) - 4 ( G 0 - G 9 8 ) A*,, Ca CaOH Ca(OH), log& /J mol-l K-l /kJ mol-1 T/K 1720 1.61 x lovg 1.12 x 7.22 x -0.032 -45.1 -43.9 1753 2.42 x 3.36 x 4.33 x -0.033 -45.7 - 44.3 1773 3.22 x 5.60 x lop9 7.94 x lob9 -0.088 - 46.2 -42.7 1800 6.04 x 8.40 x 9.02 x -0.1 11 - 46.9 -42.7 1823 7.66 x 9.80 x 9.39 x -0.125 - 47.3 - 43.1 1853 8.86 x 1.12 x 1.01 x -0.147 -48.0 -43.1 1900 1.21 x lo-# 1.40 x 1.08 x -0.178 -49.5 -43.1 average - 43.1 k 2 to a A H of 420.5Ifr 16 kJ mol-1 at an average temperature of 1858 K. The AHr at 298 K was 443.1 _+ 16 kJ mol-l, resulting in a second-law Af?&98 of - 192.0+ 16 kJ mol-1 for CaOH(g), in good agreement with the third-law value. Heat of Formation of Ca(OH),(g) The heat of formation of Ca(OH),(g) was obtained by two different reactions.The first involved the reaction of water vapour with solid CaO as, CaO(c) + H,O(g) = Ca(OH),(g). ( 5 ) For this reaction the water vapour was metered directly into the cell at an ambient pressure of 3.3 x atm. Intensity data for H20(g) and Ca(OH),(g) were corrected for cross-sections and multiplier effects and converted to partial pressures via eqn (1). These pressures and values for the equilibrium constant are listed in table 3. Employing thermal values2, third-law A q g 8 values were calculated (table 3). An average of 271.1 +4 kJ mol-l led to a third-law AHfo,98 of - 605.8 f 8 kJ mol-1 for Ca(OH),(g).Values of - 635.1 and - 241.8 kJ mol-1 were used3234 Efusion Mass Spectrometry for of CaO(c) and H,O(g), respectively.22 The Do for Ca+20H was calculated as 854.8 f 8 kJ mol-l. A second-law plot of the uncorrected intensity data (fig. 1) yielded a AH, of 267.8 f 20 kJ mot1 at an average temperature of 1875 K, which became 274.0f20 kJ mol-l at 298 K. The resulting second-law AG298 for Ca(OH),(g) was - 602.5 f 20 kJ mol-l. The second reaction employed to obtain a AH, for Ca(OH),(g) was isornolecular, and gas phase only: Intensity data for the three species, corrected and converted to partial pressures, are listed in table 4. The equilibrium constant 2CaOH(g) = Ca(g)+Ca(OH),(g). (7) PCaPCa(0H)Z &aOH k, = allowed third-law AH calculations.An average third-law of - 43.1 f 2 kJ mol-l was obtained. Employing the value of - 190.8 kJ mol-l for for CaOH(g), and 179.5 kJ mol-1 for Ca(g),,, a third-law of - 603.8 f 10 kJ mol-1 and a Do of 852.7 & 10 kJ mol-l were calculated for Ca(OH),(g). The second-law AH for the isomolecular reaction (7) at an average temperature of 1803 K (fig. 1) was -33.5f20 kJ rnol-l, or -42.7f20 kJ mol-1 at 298 K. This led to a second-law value of - 603.3 f 20 kJ mol-1 for AG298 of Ca(OH),(g). These second- and third-law values for reaction (7) are in good agreement with the flow reaction data of reaction (5). Heat of Formation of KCaO(g) Obtaining thermodynamic data leading to a AHf value for KCaO(g) required a somewhat complicated effusion cell arrangement.A steady flow of H2(g) was necessary to produce CaOH(g) within the effusion cell. Simultaneously, a flow of K atoms of sufficient concentration was produced in a heated tube containing KI connected to the cell to provide a fairly constant pressure of KI(g). The three components were heated within the effusion cell to temperatures from 1880 to 1950 K to produce KCaO(g). The partial pressure of KCaO(g) was ca. 1/1000 the pressure of K(g) and l/lOUOOO the pressure of H,(g). The final reaction studied was CaOHfg) + K(g) = KCaO(g) +iH2(g). (9) The ion intensities for these four species were corrected for cross-sections and multiplier gains and converted to partial pressures via eqn (1). The partial pressures for the equilibrium constant 1 are listed in table 5. In order to obtain free-energy functions it was necessary to estimate vibrational frequencies for the new molecule KCaO(g). The estimates for the three frequencies were 300,600 and 700.The thermal functions, calculated by statistical mechanical methods,23 for the temperatures 1800, 1900 and 2000 K are listed in table 6. Employing the thermal data of table 6 for KCaO(g) and those for H2(g), CaOH(g) and K(g) from the JANAF Tables,22 the calculated thermodynamic data are listed for three temperatures, 1880, 1900 and 1950 K in table 5. An average third-law A s g 8 was calculated as -213.8f 16 kJ mol-l. Using the value of 89.1 kJ mol-1 for of K(g),,, andM . Farber, R. D. Srivastava, J. W. Moyer and J. D. Leeper 3235 partial pressures/atm - " O - %gal/ TI AK98 T/K lo4 p H 2 los pK lo8 pCaOH lo9 pKCao logk, /J mol-' K-' /kJ mo1-I 1880 3.19 2.00 1.37 3.68 3.38 - 107.1 - 228.4 1900 3.24 2.24 2.10 4.50 3.23 - 107.5 - 224.7 1950 3.28 5.04 2.80 1.00 3.10 -110.1 - 226.4 average - 226.4 It 16 Table 6.Calculated free-energy functions for KCaO(g), estimated frequencies, cc), 300, 700, 600 free-energy components/ J mol-' K-' translation - A W O - K98V TI T/K and rotation vibration electronic ( e g 8 - H,,)/T /J mol-l K-l 1800 293.5 28.6 5.8 7.8 327.9 1900 295.3 29.8 5.8 7.4 33 1 .O 2000 297.1 31.1 5.8 7.4 333.9 - 190.8 kJ mol-1 for AG298 of CaOH(g) obtained in the current study, a third-law value of - 328.0 20 kJ mol-1 was calculated for AG298 of KCaO(g). Discussion Previous published results on the thermodynamic properties of the mono- and di- hydroxides of calcium were mainly from high-temperature flames containing calcium additives.For the most part, they were in considerable disagreement as to whether CaO(g), CaOH(g) or Ca(OH),(g) was the dominant calcium species produced in the flame reactions. Flame studies of Bulewicz and S~gden,~ led to an interpretation that the predominant species was the gaseous oxide. Gurvich and Ryabova6 did not consider the dihydroxide and reported a Do for CaOH(g) of 484 32 kJ mol-l. Sugden and Schofield' employed premixed flames of H,-0,-N, in the temperature range 2135-2534 K and the Na D-line reversal method and concluded from best-fit equilibrium line plots of the possible reactions involving CaO(g), CaOH(g) and Ca(OH),(g) that Ca(OH), was the major species.They calculated a value of 908 kJ mol-1 for the Do of Ca + 20H. Cotton and Jenkins5 also employed premixed flames at somewhat lower temperatures (1570-2370 K), and by means of Li adsorption spectroscopy concluded that the con- centrations of both CaOH(g) and Ca(OH),(g) were significant. From their calculations of the equilibrium, CaOH + H,O = Ca(OH), + H, they reported Do values of 435 kJ mol-1 and 853 kJ mol-l, respectively, for CaOH(g) and Ca(OH),(g). Subsequent to these studies Kalff and Alkemadeg reported a value of 420 kJ mol-1 for the Do of CaOH(g) obtained from spectroscopic measurements in carbon monoxide-N,O flames with some water added. Conditions were chosen to make the contribution of the dihydroxide small compared to the monohydroxide concentration.This required a stoichiometric or slightly fuel-rich gas mixture. The values obtained in the previous flame studies appear to bracket the current mass spectrometer investigation. From an analysis of the various flame studies the JANAF Tables2, recommend a Do of 408f20 kJmol-l for CaOH(g) and a Do of3236 Eflusion Mass Spectrometry 860f37 kJ mol-l for Ca(OH),(g). However, since flame study results do not usually report direct measurements of the species involved, the data generally cannot be considered as definitive as mass spectrometer intensity measurements, which lead to fairly precise concentrations. In this respect the recommended values for Do of CaOH(g) and Ca(OH),(g) are 404+ 8 kJ mol-1 and 853 + 10 kJ mol-l, respectively. The thermodynamic data obtained in this study for KCaO(g) are the first reported.The value of -328f20 kJ mol-1 for of KCaO(g) is some 159 kJ mol-1 more negative than that calculated from bond energies, ca. - 159 kJ mol-l. The higher degree of stability was also found in the previous study on KAlO(g) and KSiO(g)., Potassium replacing hydrogen in several metallic compounds in high-temperature flame reactions produced stable species. These included KHMoO,, K,MoO,, KHVO,, K,VO,, KHCrO,, K,CrO, and KHFe0,.3 The K substitution for hydrogen evidently produces an ionic bonding, contributing to the stability. The authors thank the Southern California Edison Company for sponsoring this work. References 1 M. Farber, R. D. Srivastava and J. W. Moyer, J. Chem. Thermodyn., 1982, 14, 1103. 2 M. Farber, R.D. Srivastava and J. W. Moyer, High Temp. Sci., 1983,16, 153. 3 M. Farber, R. D. Srivastava, J. W. Moyer and J. D. Leeper, High Temp. Sci., 1986, 21, 17. 4 M. Farber, R. D. Srivastava, J. W. Moyer and J. D. Leeper, J. Chem. SOC., Faraday Trans. I , 1985,81, 5 D. H. Cotton and D. R. Jenkins, Trans. Faraday SOC., 1968, 64, 2988. 6 V. G. Ryabova and L. V. Gurvich, Teplofiz. Vys. Temp., Akad. Nauk SSSR, 1965, 3, 318. 7 T. M. Sugden and K. Schofield, Trans. Faraday SOC., 1966, 62, 566. 8 V. G. Ryabova, A. N. Khitrov and L. V. Gurvich, Teplofiz. Vys. Temp. Nauk SSSR, 1972, 10, 744. 9 P. J. Kalff and C. Th. J. Alkemade, J. Chem. Phys. 1973, 59, 2572. 913. 10 US. Natl. Bur. Stand. Tech. Note 270-6 (1971). 1 1 M. Farber, M. A. Frisch and H. C. KO, Trans. Faraday SOC., 1969,65, 3202. 12 M. Farber and R. D. Srivastava, Combust. Flame, 1973, 20, 33. 13 M. Farber, R. D. Srivastava and M. Uy, J. Chem. SOC., Faraday Trans. 1, 1972, 68, 249. 14 M. Farber and R. D. Srivastava, J. Chem. SOC., Faraday Trans. 1, 1974, 70, 1581. 15 M. Farber and R. D. Srivastava, J. Chem. SOC., Faraday Trans. 1, 1977,73, 1672. 16 M. Farber and R. D. Srivastava, Chem. Phys. Lett, 1977, 51, 307. 17 M. Farber and R. D. Srivastava, J . Chem. Phys., 1981,74, 2160. 18 J. B. Mann, J . Chem. Phys., 1967,46, 1646. 19 M. Farber and R. D. Srivastava, J. Chem. SOC., Faraday Trans. I , 1973, 69, 390. 20 R. F. Pottie, J. Chem. Phys., 1966, 44, 916. 21 J. W. Otvos and D. P. Stevenson, J. Am. Chem. SOC., 1956,78, 546. 22 JANAF Thermochemical Tables (Dow Chemical USA, Midland, Michigan, 1975). 23 J. E. Mayer and M. G. Mayer, Statistical Mechanics (John Wiley, New York, 10th edn, 1963). 24 E. M. Bulewicz and T. M. Sugden, Trans. Faraday SOC., 1959, 55, 720. Paper 61924; Received 13th May, 1986

ISSN:0300-9599    

DOI:10.1039/F19878303229

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I , 1987, 83 (1 l), 3237-3248 The Inclusion of Pyronine Y by p- and y-Cyclodextrin A Kinetic and Equilibrium Study Robert L. Schiller, Stephen F. Lincoln" and John H. Coates" Department of Physical and Inorganic Chemistry, University of Adelaide, South Australia 5001, Australia Temperature-jump spectrophotometric studies show the dye pyronine Y (PY) in its monovalent cationic form to be included by y-cyclodextrin (yCD) in a fast step to form a 1 : 1 complex (PY -yCD), which is followed by the slower formation of the 2: I complex (PY),. yCD, in which pyronine Y dimerizes. There is also evidence for the formation of a 2:2 complex (PY), . (yCD), in a third and fast step. The temperature-jump relaxation data obtained at 298.2 K from 1.0 mol dm-3 NaCl aqueous solutions at pH 6.1 yielded the apparent stability constants Kl = (1.OkO.l) x 107 dm3 mol-', K , = (1.2 k 1.1) x lo5 dm3 mol-l and K3 = 52 & 22 dm3 mol-I for these complexes, and the rate constants k, = (1 -7 & 1 .O) x lo9 dm3 mol-' s-' and k-, = (1.4k0.5) x lo4 s-l for the second complex. In the presence of BCD the 1 : 1 PY .pCD and 1 : 2 PY .(pCD), complexes are formed, but no complexation of PY by crCD was detected.The a-, p- and y-cyclodextrins (CD) are six-, seven- and eight-membered a-1,4-linked cyclic oligopers of D-glucopyranose, with internal annular diameters of 5-6, 7-8 and 9-10, A respectively, which form inclusion complexes with a wide range of sub~trates.'-'~ This presents an opportunity to study the effect of cyclodextrin size on both the stability and lability of inclusion complexes.The majority of such studies of the cyclodextrin inclusion complexes have been thermodynamic in nature, however, and few kinetic studies have been reported until Several organic dyes have proved to be good probes for cyclodextrin inclusion processes, and in this study the pyronine Y cation (PY), whose structure is shown below, is used as a probe to determine the kinetic and related aspects of inclusion complex formation by a-, /-I- and y-CD. Experiment a1 Pyronine Y was obtained from Sigma as a sample of ca. 60 % purity. The major impurity was a water-insoluble material. Purification of the dye by recrystallisation, chro- matographic and extraction methods was unsuccessful. In consequence of this, aqueous PY solutions were filtered through a millipore filter (0.22 pm), which removed all detectable insoluble impurities, and the PY concentration was calculated from spectrophotometric measurements at 545 nm using a molar absorbance of 8.1 x lo4 dm3 mol-' cm-' from the 1iterat~re.l~ The a-, p- and y-cyclodextrins (Sigma) were stored as the anhydrous material over P,O, in a vacuum desiccator prior to use. A.R.grade NaCl (B.D.H.) was used as the supporting electrolyte in all solutions investigated, which were prepared by weight in doubly distilled water. As PY adsorbs slightly on glass surfaces, but not significantly on silica surfaces, precautions similar to those described 32373238 Inclusion of Pyronine Y by Cyclodextrins for the earlier crystal violet studiesg were taken in order to ensure that all volumetric glassware surfaces had a similar history and that significant variations in the amount of PY adsorbed did not arise.All solutions were prepared immediately prior to spectrophotometric study, and exposure to light was kept to a minimum. Visible spectra were determined in silica cells using a Zeiss DMR 10 double-beam spectrophotometer equipped with a thermostatted ( f 0.1 K) cell block. All spectra were run in duplicate, recorded digitally onto paper tape at 1 nm intervals over the range 450-650 nm, and were analysed using a Cyber 173 computer. Temperature-jump spectrophotometric studies were performed at 555 nm for the PCD system, and at 533 and 553 nm for the yCD system, on equipment constructed in these laboratories to a design similar to that described in the 1iterat~re.l~ In the studies of the PYxyclodextrin systems a temperature-jump cell of optical pathlength l.00cm was used.The temperature jump was 8.8 K and the heating time was ca. 2 ps. To study the dye alone, a cell of optical pathlength 0.23 cm was used for which the temperature jump was 9.7 K and the heating time was ca. 5 ,us. The observation temperature was 298.2k0.1 K. Photomultiplier voltages from each transient were collected as 4096 8-bit data points using a Data LabDL91O transient recorder and stored on magnetic tape. For each solution six transients were averaged and subjected to kinetic analysis using a Computer Products Spectrum I1 minicomputer. Results Equilibrium and Spectroscopic Aspects The visible spectrum of pyronine Y exhibits no variation in the pH range 2.00-7.00, consistent with its existence as a monovalent cation at pH 6.10 in aqueous 1 .OO mol dm-3 NaCl at 298.2 K, which were the experimental conditions used throughout this study.The visible spectra of PY alone, and in the presence of yCD, are shown in fig. 1. There is a shift of the absorbance maximum to shorter wavelengths and a pronounced change in the shape of the spectrum as yCD concentration increases. (36 solutions were studied in which yCD concentration was varied in the range 0-9.51 x mol dm-3 and the PY concentration varied from 8.4 x mol dm-3.) These spectral changes are consistent with the dimerization of PY14* 16, l7 being enhanced on formation of the yCD inclusion complexes, as has been observed for other The near approach to an isosbestic point suggests that, while two species dominate the observed spectral variation, a third species is also present consistent with equilibria (1) and (2) to 1.04 x kl k-1 k, k-2 PY + yCD S PY - yCD (Kl) (fast) (1) PY + PY - yCD +(PY), yCD (K,) (slow) (2) in which PY yCD is a 1 : 1 complex and (PY); yCD is a 2: 1 complex in which PY is included as a dimer.However, when the molar absorbances of PY - yCD and (PY), . y.CD were varied during the fitting procedure, using program DATAFIT, it proved impossible to obtain a unique fit of the spectral data to these two equilibria through eqn (3), consistent with the formation of PY - yCD causing a small spectral change by comparison to (PY), - yCD. Accordingly, the approximation was made that the spectrum of PY - yCD was identical to the known spectrum of PY, and Kl and K , values of (1.1 If: 0.5) x lo2 and (5.3 2.5) x lo5 dm3 mol-1 (where the errors represent one standard deviation), respectively, were obtained from a fit of the absorbance data to the equation in the ranges 505-525 and 535-565 nm at 1 nm intervals. The derived (PY);yCD spectrum, which is qualitatively similar to that of (PY),,14 is shown in fig.2.R. L. Schiller, S. F. Lincoln and J. H. Coates 3239 h/nm Fig. 1. Variation of the PY spectrum in the presence of yCD at pH 6.10 in aqueous 1 .OO mol dm-3 NaCl at 298.2 K. The molar absorbance at 550 nm decreases systematically as total [yCD] increases sequentially in the range 0, (1.03, 2.10 and 3.99) x and (1.00, 2.51, 5.02 and 9.51) x lop3 mol dm-3, with total [PY] varying in the range (8.4-10.4) x lop6 mol dmP3.These 10 spectra exemplify the spectral variation observed for all 36 solutions studied. (1.00, 2.00 and 5.02) x Fig. 2. The PY . (/ED), derived as3240 Inclusion of Pyronine Y by Cyclodextrins Analysis of the (PY), - yCD spectrum according to exciton theory," using program EXCITON, indicates that the transition moments of the PY monomers (along the long axis of the xanthene entity) are aligned at an angle of 20-25" to each other in (PY);yCD, in contrast to (PY),, in which the analogous angle is zero.14 This difference may arise from constraints imposed on the dimer by inclusion in the yCD cavity, but could also be to some extent an artefact arising from the approximations used in deriving Kl and K,.Nevertheless, the major spectral variations shown in fig. 1 remain consistent with dimer inclusion through equilibria (1) and (2). The variation of the spectrum of PY in the presence of PCD in the concentration range 0-1 .OO x lo-, mol dm-3 is substantially less in magnitude than that observed in the presence of yCD, and shows no evidence for the enhancement of PY dimerisation through inclusion as is seen from fig. 3. At total [PCD] < 8 . 0 0 ~ lo-" mol dm-3 the spectra exhibit an isosbestic point at 511 nm. At greater total [PCD] further spectral changes occur and a second isosbestic point arises at 547 nm. The appearance of these two isosbestic points is consistent with PY forming two complexes PY-PCD, and PY * (PCD),, according to eqn (4) and ( 5 ) : kl k l PY+PCD+PY*PCD (Kl) k; PCD+PY-PCD + PY*(PCD), (Ki) k;k12 (4) The spectra of 25 solutions were fitted to eqn (6) and the stability constants Kl = (5.2+ 1.2) x la dm3 mol-', and Ki = (1.7 k0.4) x 102 dm3 mo1-1 were determined from the molar absorbances in the range 515-560 nm.These Kl and Ki values were used to calculate the spectra of PY -pCD and (PY), .PCD shown in fig. 3. It is seen from fig. 2 that the spectral change induced in PY on inclusion by PCD is quite small. The spectrum of PY was found to be insignificantly changed in the presence of aCD, indicating a low stability for PY - aCD. The dimerization of PY was investigated by temperature jump spectrophotometry. In the total [Pyl range (1.77-8.23) x mol dm-3 a relaxation characterised by a decrease and an increase in absorbance at 517 and 547 nm, respectively, was observed.The larger relaxation amplitude change occurred at 547 nm, and at both wavelengths the relaxation amplitude increased markedly with concentration. Over the total [Pyl range studied the relaxation occurred within the instrumental heating time (ca. 5ps) and therefore no quantitative kinetic data could be derived. However, the variation of the relaxation amplitude (AI) with the total [Pyl was consistent with that expected for the PY dimerisation equilibrium : kd 2 p y =(py)2 (Kd) (7) k-d which is of the form of eqn (8) in which I, is the detected light intensity prior to the temperature jump and C is a constant characterising the dimerisation equilibrium." The variation of AI/I, with total [Pyl is shown in fig.4, as is the best fit of these data to eqn (8) obtained through a non-hear least-squares analysis using program DATAFIT, which yielded Kd = (1.1 k0.2) x lo3 dm3 mol-' at 298.2 K. This compares with Kd = (2.0f 0.1) x lo3 dm3 mol-' reported in lop3 mol dm-3 hydrochloric acid." Ohling'' has shown this dimerisation equilibrium to be characterised by k, = 2.3 x lo9 kg mol-1 s-l and k-, = 1.7 x lo5 s-l in 1.0 mol kg-' aqueous sodium chloride at 293.2 K and at a pressure of 5 MPa.R. L . Schiller, S. F. Lincoln and J. H. Coates 3241 10 r( I I r( - E E 0, 1 5 8 9 e s kl E U 0 .o - 0 0 10 - I v) I r( - 0 E E rn a t z 5 0 5 e 2 .o c.l - z 60 0 0 500 X/nm Fig. 3. Variation of the PY spectrum in the presence of PCD at pH 6.10 in aqueous 1 .OO mol dm-3 NaCl at 298.2 K.In (a) the molar absorbance at 550 nm increases systematically as total WCD] increases sequentially in the range 0, 9.90 x (2.02, 5.02 and 7.02) x lop4 mol dm-3. In (b) the molar absorbance at 550 nm decreases systematically as total [PCD] increases sequentially in .the range (1.00, 2.00, 5.00, 7.01 and 9.02) x lop3 mol dm-3, with the spectrum characterised by the lowest molar absorbance being that of PY alone. Total [PY] varied in the range (1.19- 1.35) x lop5 rnol dm-3. These spectra exemplify the spectral variation observed for all 25 solutions studied. Kinetic Aspects Temperature-jump spectrophotometric studies of PY (total [Pyl range 8.4 x 1 0-6 - 10.8 x low6 mol dm-3) and YCD (total [yCD] range 1.57 x 10-4-l.004 x mol dm-3) at 517 and 547 nm detected a single relaxation at both wavelengths. (The amplitude of the relaxation attributed above to the dimerization of free PY was < 1 O h of that of the relaxation observed in the yCD solutions.) At 517 nm the relaxation was characterised by a decrease in absorbance, whereas at 547 nm the relaxation produced an increase in absorbance, and also the greater absorbance change.The reciprocal relaxation times, 1 /z, determined at both wavelengths were identical within experimental error, and are plotted against total [yCD] in fig. 5. This variation of l / z is consistent with the two equilibria shown in eqn (1) and (2), where the first equilibrium is sufficiently fast to be in equilibrium throughout the relaxation of the second equilibrium.Under these conditions the variation of l/z is given by (9) 1 /z = k,[PY]([PY * yCD] + [Pyl+ 4[yCD])/([PY] + [yCD] + 1 / K l ) + k-,3242 Inclusion of Pyronine Y by Cyclodextrins 0.3 0.2 %O 0.1 I I I I I I 0 2 4 6 a [ PY ]/ 1 0-5 mol dm-3 Fig. 4. The variation of AI/Io with total [PY] at pH 6.10 in aqueous 1.00 mol dmP3 NaCl at 298.2 K. The solid curve represents the best fit of the data to eqn (8). [ $D]/ 1 0-3 mol dmd3 Fig. 5. The variation of l / z (298.2 K) for the PY-yCD system with variation of total [yCD] at pH 6.10 in aqueous 1.00 rnol dm-, NaCl at 298.2 K. Total [PY] varied in the range (8.4-10.8) x mol dm-,. The solid curve represents the best fit of the data to the three step model, eqn (1 1). The best fit curve for the two step model, eqn (9), differs little and is not shown.where all concentrations are the equilibrium values existing after the relaxation, as is also the case for eqn (1 1) and (12). A non-linear least-squares fit of the l/z data to eqn (9) yields k, = (1 .O k 0.7) x lolo dm3 mol-1 s-l, k-, = (3.3 2.2) x lo3 s-l, Kl = (1.13 & 0.07) x lo3 dm3 mol-1 and K, = (3.0k4.1) x lo6 dm3 mol-l. The sum of the squares of the residuals for the fit of the l / z data to eqn (9) is 2.17 x lo8. The 1 /z data are also consistent with a reaction sequence involving the fast formation of (PY), - (yCD), : k3 k-3 yCD + (PY), - yCD + (PY), * (yCD), (K,). (10)3243 R. L. Schiller, S. F. Lincoln and J. H. Coates The l/z variation is now accommodated by the three equilibria shown in eqn (l), (2) and (lo), where the first and third equilibria are sufficiently labile to be at equilibrium throughout the relaxation of the second equilibrium.(Evidence has been adduced for the formation of analogous 2:2 complexes between yCD and methyl orange' and tropaeolin.lO) Under these conditions the variation of 1 /z with yCD concentration is given by l/z = k,[PY]([py * yCD] + [py] + 4[yCD])/([PY] + [yCD] + 1 /Kl) + k-,([(PY)2 * YcDI + l/K3)/([7CD] + [(PY), yCD] + l/K3). (1 I ) A non-linear least-squares fit of the l / z data to eqn (1 I), shown in fig. 5, yielded k, = (1.7 K, = ( 1 .O 0.1) x lo3 dm3 mol-l, K, = (1.2 rt 1.1) x lo5 dm3 mol-1 and K3 = 52 22 dm3 mol-1 at 298.2 K. The sum of the squares of the residuals for this data-fit to eqn (1 1) was 3.3 x los.[Eqn (9), (1 l), (12), and (13) may be derived using the methods of Bernasconi20 and Czerlin~ki.~'] The K, and K, values determined from the l/z data and from the spectrophotometric equilibrium studies using the two-equilibrium model [eqn ( 1) and (2)] differ substantially. The value [(PY), * (yCD),] calculated on the basis of the K,, K2 and K3 values determined from the 1 /z data through the three-equilibrium model [eqn (I), (2) and (lo)] is always small compared to [PY yCD] and [(PY), - yCD] over the total [yCD] range studied. This, in combination with the observation that the major spectral change in the PY-yCD system arises from the enhanced dimerisation of PY on complexation, and the probability that the spectrum of (PY);(yCD), will not differ greatly from that of (PY), - yCD, precludes a definitive choice between the two-equilibrium and the three- equilibrium models. Nevertheless, the existence of equilibria (1) and (2) is firmly established, and only the existence of the third equilibrium [eqn (lo)] is less certain. The temperature-jump induced relaxations of the PY-PCD system (in the total [Pyl and [PCD] ranges 1.28 x 10-5-1.35 x and 4.70 x 10-5-9.02 x lop3 mol dm-3, re- spectively) were considerably less in amplitude than those observed for the PY-yCD system, as anticipated from the spectral variations seen in fig.1-3. As a consequence the relaxation occurring within the instrumental heating time (and attributed to the dimerisation of PY) approached almost 10% of the magnitude of the relaxations attributable to the PCD inclusion process.Both relaxations produced an increase in absorbance at 547 nm. For total [PCD] 6 5.00 x lop4 mol dm-3 the relaxation could be resolved into two exponential curves, where the longer of the two relaxation times was attributed to relaxation of the equilibrium shown in eqn (4). For this relaxation the linear variation of l / z with total [PCD] < 5.00 x (fig. 6) is consistent with the equation (12) which describes the relaxation of equilibrium (4). A non-linear least-squares analysis of the data through eqn (12) yields k , = (1 . I k0.2) x 10' dm3 mol-' s-', k-, = (2.6 k 0.4) x lo4 s-l, and K, = (4.2 & 1.4) x lo3 dm3 mol-'. In the total [PCD] range 5.00 x -5.00 x lop3 mol dmP3 the relaxation traces were satisfactorily fitted to neither one nor two exponentials, probably as a consequence of the relaxation of the second equilibrium ( 5 ) making an increasingly important contribution to the relaxation process as total [PCD] increased. At total [PCD] > 5.00 x mol dmP3 the relaxation could once again be resolved into two exponential curves, one being characterised by a relaxation time within the instrumental heating time and the other by a longer relaxation time whose reciprocal exhibits a linear dependence on total [PCD] (fig.6). This linear dependence of 1 /z on total [PCD], which is in great excess, is attributed to the relaxation of equilibrium (9, and is described by 1 .O) x lo9 dm3 mol-1 s-', k-, = (1.4.k 0.5) x lo4 s-', 1 /z = k,([PY] + [PCD]) + k-, l/z = k;[PCDlct,tal, + kL2.(13)3244 Inclusion of Pyronine Y by Cyciodextrins ' 2 ' I 4 I I 6 I ' 8 I I 10 ' [PCDI! mol dm-3 Fig. 6. The variation of l / z (298.2 K) for the PY-PCD system with variation of total [BCD] at pH 6.10 in aqueous 1.00 mol dm-3 NaCl at 298.2 K. Total [PY] varied in the range (1.28-1.35) x mol dm-3. The solid curves in the low and high concentration ranges, respectively, represent the best fits of the data to eqn (12) and (13). A fit of the data obtained in this region yields : ki = (5.4 IfI 1.2) x lo6 dm3 mol-1 S-', k', = (2.0f0.9) x lo4 s-l and k; = (2.7_+ 1.8) x 10, dm3 mo1-l. The agreement between the K, and Ki values derived from the temperature-jump and spectrophotometric equilibrium studies indicates a reasonable internal consistency. Discussion The differing interactions of PY with a-, P- and y-CD are clearly a consequence of the systematic vari5tion of the annular diameters of these cyclodextrins in theosequence 5-6, 7-8 and 9-10 A, respectively.By comparison the dimensions of PY (A) determined approximately from CPK (Corey, Pauling, Koltun) models are: length of PY = 17; distance from tip to tip of the methyl groups in the -NMe, substituent of PY = 11.5; the smallest and largest distance perpendicular to the long axis of the superimposed xanthene entities in (PY), = 7 and 8, respectively ; and the distances between substituent nitrogens at opposite ends of (PY), = 8.5, which compares with the depth of the CD annulus = 8. These simple comparisons indicate that the -NMe, substituents prevent significant inclusion of PY by aCD, as found in this study, whereas PY fits closely into the larger annulus of PCD to form PY -PCD and PY - (PCD),, which is stoichiometrically, and probably structurally, similar to the 1 : 2 substrate PY - (aCD), complexes formed with smaller substrates.l2' l3 The decreased stability of the PY yCD complex by comparison to that of PYePCD (table 1) is probably a consequence of the relatively loose fit of PY into the larger yCD annulus.This larger annulus accommodates the (PY), dimer in (PY), - yCD whereas the analogous (PY), ./ED complex does not form to a detectable extent. The formation of (PY);(yCD), is less well established, but CPK models indicate that on stereochemical grounds its formation is possible, and the analogous complex has been observed in the methyl orange' and tropaeolinl' systems.The formation of these complexes is shown schematically in fig. 7, where the truncated cone represents the cyclodextrin annulus. This scheme also provides a basis for discussion of the data collected in table 1. The formation of 1 : 1 dye.CD complex probably occurs with the dye entering the wider end of the cyclodextrin annulus in the equilibrium characterised by k, and k-, in fig. 7. The magnitude of k, appears to be largely determined by the relative sizes of the dye and the cyclodextrin annulus. Thus for aCD, the smallest of the cyclodextrins, k, for 1 : 1 dye -aCD formation is reported to decrease over several orders of magnitude as the size of the dye increases.',' ( K , exhibits a lesser variation, consistent with these stericR.L. Schiller, S. F. Lincoln and J . H. Coates 3245 PY CD Fig. 7. Schematic representation of the inclusion of PY by PCD and yCD in which the cyclodextrin annulus is represented by a truncated cone. The formation of (PY);(yCD), is not shown. Table 1. Dyeecyclodextrin inclusion complex equilibrium and kinetic parameters (298.2 K) Kl/ 1 O2 ~ ~ 1 0 5 K3/ 1 O2 k2/ 109 k2/ lo3 dye dm3 mol-' dm3 mol-' dm3 mol-' dm3 mol-'s-l S-' pyronine Y" pyronine Yb pyronine Bc tropaeolind methyl orangee crystal violetf pyronine B" tropaeolind pyronine Yg y-cyclodextrin 11.3 k0.7 30f41 - 10f7 3.3 & 2.2 lo+ 1 1.2+ 1.1 0.52k0.22 1.7f 1.0 14+ 5 4.18k1.47 16.8f5.4 1.77f1.54 2.27k0.61 1.35k0.23 0.45 f 0.07 20f 11 61 +25 9.4k5.1 4.8 f0.8 4.63 f 0.07 10.3 Ifr 0.9 - 1.73 f 0.08 1.68 f 0.07 4.3 f 0.1 1.28 f 0.04 - 0.82 f 0.02 6.40 f 0.05 P-cyclodextrin (k1/109 = 0.11 fO.01 dm3 mol-'s-'; k-,/103 = 15+5 s-') - - - 73+31 - 7.1 f0.7 40 Ifr 70 - 5 f 6 1.3 f 1.5 KJ lo2 K2/ 102 ki/ 1 O6 kL2/ 103 dm3 mol-' dm3 mol-' dm3 mol-l s-' S-' P-cyciodex trin 42f 14 2.7 f.1.8 5.4+ 1.2 20f.9 (kl/109 = 0.1 1 f0.02 dm3 mol-' s-'; k-,/1O3 = 26f4 s-l) a This work, two-step model. * This work, three-step model. Ref. (11). Ref. (10). Ref. (8). Ref. (9). This work.3246 Inclusion of Pyronine Y by Cyclodextrins interactions affecting k, and k-, to a similar extent.) As the size of the annulus increases, steric interactions between the dye and the cyclodextrin should decrease and k, should increase for a given dye. The non-detection of PY aCD suggests that the annulus of aCD is too small for the stable inclusion of PY, and in consequence the only k, value determined in this study is 1.1 x 10' dm3 mol-1 s-l for PY -PCD, which is identical to the value observed for the very similar pyronine B complex (pyronine B has ethyl substituents in place of the pyronine Y methyl substituents). The subsequent slower formation of PY .(pCD), (ki and k:,) suggests that the second PCD experiences an increased steric hindrance in its complexation of PY .PCD.The rate laws [eqn (9) and (1 l)] and mechanism (fig. 7) proposed for the formation of PY - yCD and (PY), - yCD require that k, and k-,, respectively, are substantially greater than k, and k-, as discussed above. As the annulus of yCD is larger than that of PCD it is expected that k, characterising PY -PCD is substantially larger than k, = 1.1 x 10' dm3 mol-1 s-l characterising PY yCD, and may approach the diffusion-controlled limit.(Similarly large k, values are also anticipated for the other 1 : 1 dye - yCD complexes in table 1.) A subsequent and slower inclusion of a second PY produces (PY);yCD characterised by k, and k-, in fig. 7. Pyronine Y is the fifth dye for which inclusion by yCD produces a l/z dependence of the type seen in fig. 5, and in which the stability of the included dye dimer in (dye), yCD is increased by several orders of magnitude over that in the free state.'-" CPK models indicate that the entrance of the second dye monomer into the annulus to form (dye), - yCD is relatively hindered.Nevertheless, the magnitude of k, is large and varies by a factor of 12 over the five dyes; and k-, varies by a factor of 10. These variations are surprisingly small in view of the substantial structural differences between the dyes, and the existence of pyronine B, pyronine Y and crystal violet as monovalent cations, and tropaeolin and methyl orange as monovalent anions under the conditions of the inclusion studies. This suggests that either there is a fortuitous combination of interactions controlling k, and k-, characterising (dye), - yCD to produce the modest variation in these rate constants, or that some interactions are particularly dominant in the systems appearing in table 1, as considered below. It is now appropriate to examine both the variation of k, and k-, for the dimerisation of a range of d y e ~ ~ ~ v ~ ~ - ~ ~ in the free state [eqn (7)], and the variation of k, and k-, for the dimerisation of the dye in (dye);yCD [eqn (2)].This is achieved through an examination of fig. 8, in which plots of log k, and log k-, against log K , are shown together with plots of logk, and logk-, against logK, (table 1). The solid curves represent the linear least-squares fits of the data to log k, = m log K, + c for which m = 0.07 and c' = 8.8f0.3. The greater (negative) value of m' by comparison with the value (positive) of rn indicates that the variation of k, with the nature of the free dye is largely determined by the rate of dissociation, whilst the rate of dimer formation shows only a small dependence on the nature of the dye.This suggests that the diffusional characteristics of the dyes may limit the variation in K,, whereas disruption of the secondary forces between the dye molecules in the dimer largely determines k-,. (A group of three dyes exhibit substantially lower values for k, and k-, than expected from the data pertaining to the other ten dyes. The reason for this is unclear.) It is also apparent from fig. 8 that the (dye), * yCD log k, and log k-, values are quite close to the best fit lines for log k, and log k-,, respectively. This suggests that the increased stability of the dimer in (dye), - yCD is largely a consequence of k-, being substantially less than k-,, as is seen (fig. 8) to be the case for PY, whose dimerisation has been kinetically characterised in the free state and in (PY), yCD.[The dimerisation equilibrium for pyronine B, tropaeolin, methyl orange, and crystal violet is also more facile than the dimerisation involving the corresponding (dye), yCD complexes. 11] The magnitudes of k,, k-, and k, are largely dominated by the properties of the dyes, whereas the difference in magnitude of k-, and k-, reflects the change of dimer environment from the free state 0.06 f 0.07 and C = 8.8 f 0.3; and log k-, = m' log Kd + C' for which m' = - 0.94 &R. L. Schiller, S. F. Lincoln and J. H. Coates 3247 c 20 0- 0 2t 0 14 01 I I I a I I 0 2 4 6 log (Kd/dm3 mol-’) log(K2/dm3 mol-’) Fig. 8. Plot of logk, and logk-, against log& for the dimerisation of the following dyes: (1) dimethyladenine,22 (2) ethidium (3) p r ~ f l a v i n , ~ ~ (4) p r o f l a ~ i n , ~ ~ ( 5 ) thironine,26 (6) rhodamine 6G,27 (7) thironine,28 (8) methylene blue,29 (9) pyronine Y,17 (10) acridine orange,3o (1 1) acridine (14) congo red,34 (1 5 ) rhodamine B35 and (16) rhodamine 3B.35 The solid curves represent the linear least-squares fits of the data to the equations log k, = m log K, + c, and log k-, = m’ log Kd + c’.The log k,, log k-, and log K2 data for dimer inclusion in (dye);yCD where the dyes are: (17) pyronine Y (this work), (18) pyronine B,ll (19) crystal ~ i o l e t , ~ (20) methyl orange,s and (21) tropaeolin’” are also plotted; as also are the data for (22) tropaeoling in (tropaeo1in);PCD. (12) acridine orange,32 ( I 3) Biebrich to that of the inclusion complex. Thus the decreased dimer dissociation rate in (dye), .yCD is probably a consequence of the solvational changes and motional restrictions experienced by (dye), in the yCD annulus. We thank the Australian Research Grants Scheme for partial support of this research, and Dr Tom Kurucsev for the use of his programs EXCITON and DATAFIT and for advice on some spectroscopic aspects of this study. References 1 M. L. Bender and M. Komiyama, Cyclodextrin Chemistry (Springer, Berlin, 1978). 2 W. Saenger, Angew. Chem., Int. Ed. Engl., 1980 19, 344. 3 I. Tabushi, Acc. Chem. Res., 1982, 15, 66. 4 J. Szejtli, Cyclodextrins and Their Inclusion Complexes (Akademiai Kiado, Budapest, 1982). 5 R. Breslow, Chem. Br., 1983, 126. 6 F. Cramer, W. Saenger and H-Ch. Spatz, J. Am. Chem. SOC., 1967, 89, 14.7 A. Hersey and B. H. Robinson, J . Chem. SOC., Filraday Trans. I , 1984, 80, 2039.3248 Inclusion of Pyronine Y by Cyclodextrins 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 R. J. Clarke, J. H. Coates and S . F. Lincoln, Carbohydr. Res., 1984, 127, 181, R. L. Schiller, J. H. Coates and S. F . Lincoln, J . Chem. SOC., Faraday Trans. I , 1984, 80, 1257. R. J. Clarke, J. H. Coates, and S. F. Lincoln, J. Chem. SOC., Faraday Trans. I , 1984, 80, 3119. R. L. Schiller, S. F. Lincoln and J. H. Coates, J. Chem. SOC., Faraday Trans. I , 1986, 82,2123. In this reference ‘annular radii ’ should read ‘annular diameters ’. D. L. Pisaniello, S. F. Lincoln and J. H. Coates, J, Chem. SOC., Faraday Trans. I , 1985, 81, 1247. I. M. Brereton, T. M. Spotswood, S. F. Lincoln and E. H. Williams, J. Chem. Soc., Faraday Trans. I , 1984, 80, 3147. L. P. Gianneschi, A. Cant and T. Kurucsev, J. Chem. SOC., Faraday Trans. 2, 1977, 73, 664. G. G. Hammes, in Techniques ofchemistry, ed. G. G. Hammes (Wiley, New York, 1974), vol. VI, part 2. J. Gormally and S . Higson, J. Chem. SOC., Faraday Trans. I , 1986, 82, 157. W . Ohling, Ber. Bunsenges. Phys. Chem., 1984, 88, 109. L. P. Gianneschi and T. Kurucsev, J . Chem. SOC., Faraday Trans. 2, 1976, 72, 2095. D. Thusius, J . Am. Chem. SOC., 1972, 94, 356. C. F. Bernasconi, Relaxation Kinetics (Academic Press, New York, 1976). G. H. Czerlinski, Chemical Relaxation (Marcel Dekker, New York, 1966). D. Porshke and F. Eggers, Eur. J. Biochem., 1972, 26, 440. D. H. Turner, R. Yuan, G. W. Flynn and N. Sutin, Biophys. Chem., 1974, 2, 385. T. G. Dewey, D. A. Raymond and D. H. Turner, J. Am. Chem. SOC., 1979, 101, 5822. D. H. Turner, G. W. Flynn, S. K. Lundberg, L. D. Faller and N. Sutin, Nature (London), 1972, 239, 215. W. Inaoka, S. Harada and T. Yasunaga, Bull. Chem. SOC. Jpn, 1978, 51, 1701. W. Inaoka, S. Harada and T. Yasunaga, Bull. Chem. SOC. Jpn, 1980, 53, 2120. T. G. Dewey, P. S. Wilson and D. H. Turner, J. Am. Chem. SOC., 1978, 100, 4550. W. Spencer and J. R. Sutter, J, Phys. Chem., 1979, 83, 1573. G. G. Hammes and C. D. Hubbard, J. Phys. Chem., 1966, 70, 1615. B. H. Robinson, A. Seelig-Loffler and G. Schwarz, J . Chem. Soc., Faraday Trans. I , 1975, 1, 815. G. Schwarz and W. Balthasar, Eur. J. Biochem., 1970 12, 461. D. N. Hague, J. S. Henshaw, V. A. John, M. J. Pooley and P. B. Chock, Nature (London), 229, 191. T. Yasunaga and S . Nishikawa, Bull. Chem. Soc. Jpn, 1972, 45, 1262. M. M. Wong and Z. A. Schelley, J. Phys. Chem., 1974, 78, 1891. Paper 61997; Received 22nd May, 1986

ISSN:0300-9599    

DOI:10.1039/F19878303237

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. I, 1987, 83 (1 l), 3249-3258 Thermodynamic Properties of Concentrated Heteroionic Polyelectrolyte Solutions Horacio R. Corti Departamento de Quimica Inorganica, Analitica y Quimica Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabelldn 2, Ciudad Universitaria, Nuiiez, Cap. Federal, Argentina The water sorption isotherms of concentrated sodium-caesium polystyrene sulphonate solutions have been measured as a function of the ionic composition at 298.15 K. Also the densities of the solid-like solutions are reported at various water contents. The systems obey the B.E.T. isotherm only over a limited range of concentration, but empirical equations have been found which describe the behaviour of the linear and crosslinked ion- exchangers over the concentration range of practical interest.The heteroionic systems studied here are far from ideal behaviour ; anomalies are found in the sodium-rich region, probably caused by a lattice-like structure involving caesium ions. It is known that the water uptake of a polyelectrolyte in a given ionic form largely depends on its ion-exchange capacity and degree of crosslinking. The crosslinked polystyrene sulphonate system (resin)' or concentrated solutions of the linear form2. have been studied in relation to their thermodynamic properties, and the effect of different counterions on the water sorption and partial molar volume has also been discussed. 4 3 However, the literature is not abundant with regard to heteroionic systems (i.e. systems where two or more counterions are bonded to the macroion) even though these are the case in most practical applications of ion-exchangers.In this work the sodium-caesium form of linear polystyrene sulphonate solutions (NaPSS-CsPSS) has been studied in relation to its water sorption and partial molar volume in order to compare its thermodynamic behaviour with the homoionic pure components. It is well known6-' that the water content in homoionic resins has a strong influence over its transport properties (intradiffusion, conductivity, etc.) and relatively simple relationships can describe changes in the transport coefficients with the fraction volume of polymer, q5p, or the reciprocal of the number of water molecules per ionic group, q, usually called the swelling variable. A study of the thermodynamic properties of this heteroionic system is in consequence a prior stage for analysing its transport properties in a forthcoming paper.Our system is composed of water as swelling agent (0) and a mixture of sodium (1) and caesium (2) polystyrene sulphonate. The concentration and composition of this system is described by the swelling variable and the ionic equivalent fraction, defined by where no is the number of moles of water and np = n, +n2 is the total number of moles of polyelectrolyte. 32493250 measurements and is described by Thermodynamic Properties of Poly elec t r oly te S o h t ions The volume of one equivalent of polyelectrolyte can be obtained from density YO = qv,+ 6 (3) where v,=Ylv,+Y,I/, (4) and 6, obtained by using the Gibbs-Duhem equation, so at fixed P, T and y it follows that and are the partial molar volumes of the components.& and l/p are and 6 = (F) Y The swelling variable is obtained from sorption-isotherm experiments, where the activity of water a, (=p/p,) is fixed. In this case the Gibbs-Duhem equation, dG, = -dG, (7) can be integrated to obtain the Gibbs free energy of hydrationg AGh = qRTlna,-RT q dlna, Lo where the second term on the right is the free-energy change for the hydration of the polyelectrolyte at constant composition. AGh can be easily obtained by numerical or graphical integration. Experimental Materials The polystyrene sample, Lustrex HF-55 Cristal 105, was purified by dissolution in benzene and precipitated with methanol.The method of sulphonation has been described elsewhere. The dilute solution of polystyrene sulphonic acid (HPSS) was converted into the sodium form in an exchange column. Part of this sodium salt (NaPSS) was transformed into the caesium salt (CsPSS) in a similar way. Salt mixtures were prepared from concentrated solutions of the pure salts, and their sodium/caesium ratios were determined by flame spectrophotometry. Pure NaPSS was also used to facilitate comparisons with previous result^.^ The exchange capacity of the HPSS was measured by ion exchange in aqueous NaCl and titration with alkaline solution. The exchange capacity, C, for HPSS was 0.005 24 mol g-' (ca. 96.5 % sulphonated). The equivalent mass of the salt mixture (the inverse of the exchange capacity) is determined by the composition of the mixture: @=YlMl+Y,M, (9) where M, and M, are the equivalent masses of the pure NaPSS (1) and pure CsPSS (2), respectively, and y is the equivalent fraction defined by eqn (1).Table 1 shows the main characteristics of the polyelectrolytes used in this work. Equilibrium Properties Water sorption by resins was determined by isopiestic equilibration of the polyelectrolyte samples with saturated electrolyte solutions of known water activity'' in specially designed ves~els.~ All the measurements were carried out at 25 5 0.01 "C on four samples for each composition and water activity, until a constant weight was achieved.H. R. Corti 325 1 Table 1. Ionic composition, exchange capacity and molecular mass of the polyelectrolyte samples salt Yz C/mmoI 8-l M / g mol-' HPSS - 5.24 190.8 NaPSS 0.000 4.70 212.8 f 0.7 Na-CsPSS 0.148 f.0.004 4.36 229.1 f 0.4 Na-CsPSS 0.391 IfI0.008 3.91 255.7 k 0.9 Na-CsPSS 0.702 f 0.012 3.45 289.9 f 1.3 Na-CsPSS 0.861 f 0.007 3.25 307.3 & 0.8 Equilibration times ranged between 10 days to 2 months depending on the water activity of the isopiestic solution. Finally, each sample was dried under vacuum at 110 "C to obtain the resin mass fraction, xp, defined by (10) mP x p = ____ mo +m, where mp and m0 are the masses of resin and water in the sample, respectively. The reproducibility of xp was better than 0.1 YO. The swelling variable, q, is then obtained from xp: -The densities of the Na-CsPSS samples were measured by a flotation method. At water activities (a) below 0.93 all the samples were solids and were prepared in the form of small strips which were immersed in a mixture of dibutylphthalate (p = 0.969 g cm-l) and 1,2-dibromoethane (p = 0.179 g cm-'). The composition of the liquid mixture was adjusted to match the density of the sample and was finally measured with a Mohr balance (accuracy 0.0002 g cm-l) with a reproducibility of 0.001 g cm-l.The equivalent volume of the polyelectrolyte solution can be expressed in terms of the measured quantities as v o = M/px,. (12) Results Table 2 shows the equilibrium properties of the polyelectrolyte solutions. The densities of the solutions at water activities of 0.2245, 0.6183, 0.8071 and 0.9248 have been obtained by interpolation procedures. The equivalent volume calculated from experimental data by means of eqn (12) is also shown in fig.1 as a function of q. Values of & and V were obtained from the slope and its extrapolation to q = 0 as indicated by eqn ( 5 ) and (6). The results are listed in table 3 as a function of the ionic composition for 2 < q < 9. In this range of concentration the partial molar volume of water is lower than the pure-water value (18.068 cm3 mol-l) and is even lower for q < 2 as a consequence of strong interactions of the water molecules with the ions and charged groups on the polymer chain. The inset of fig. 1 shows the change in the equivalent volume of dry polyelectrolyte, Vp", with the ionic composition. Some density measurements performed on dilute solutions (q > 20) are shown in fig.2 as a function of the equivalent concentration. The relationship p = po +A'@ (13)3252 Thermodynamic Properties of Polyelectrolyte Solutions Table 2. Density and water uptake of Na-CsPSS solutions at 298.15 K Y2 0.000 0.148 0.391 0.702 0.861 a0 0.0000 0.0703 0.2245 0.3300 0.4276 0.5286 0.6183 0.7083 0.8071 0.9019 0.9248 1 .528" 0.00 1.520 1.30 (1. 509)b 1.72 1.495 2.16 2.68 1.468 2.90 (1.439) 3.59 1.412 4.37 (1.371) 5.85 1.317 8.45 (1.304) 9.25 - 1.688 0.00 1.676 1.14 (1.641) 1.51 1.607 1.90 2.41 1.573 2.62 (1 .547) 3.14 1.513 3.82 (1.466) 5.05 1.397 7.41 (1.377) 8.25 - 1.805 0.00 1.78 1 1.04 (1.765) 1.42 1.737 1.75 2.23 1.698 2.4 1 (1.668) 2.91 1.635 3.61 4.76 1 so0 6.99 7.85 - (1 .579) (1.477) 1.919 0.00 1.901 0.99 (1.883) 1.36 1.853 1.69 2.07 1.813 2.30 (1.778) 2.80 1.739 3.44 (1.686) 4.46 1.592 6.72 (1 S60) 7.75 - 1.968 0.00 1.938 1.04 (1.090) 1.40 1.878 1.71 2.1 1 1.835 2.33 (1.797) 2.80 1.753 3.45 (1.696) 4.43 1.589 6.80 7.65 - (1.558) a In each pair of values the upper value is p / g ~ r n - ~ and the lower one is q.Values in parenthesis are interpolated. which is valid for homoionic ~ystems,~' l1 also holds for heteroionic systems. Eqn (1 3) can be expressed in terms of V o and q3: M MO vo = -(1-A)+-+ Po Po where A = A'/&? and Mo/po = & = 18.068 cm3 mol-l. By comparison with eqn (3) it follows that V,(q = 0) can be obtained from a least- squares treatment of density data for dilute solutions and their values at different ionic composition are shown in table 3. They are lower than Vp obtained from densities in the concentrated region (0 < q < 9) since for q > 20 & has reached its value in pure water, as shown in the last column of table 3.The anomalous behaviour of Vp at low caesium contents (cf. table 3) will be discussed in the next section. Fig. 3(a) shows the water sorption isotherms for Na-CsPSS while fig. 3(b) shows the swelling variable as a function of the ionic composition at fixed a, values. Discussion The water sorption isotherms show that the heteroionic systems obey the B.E.T. equation at low water contents (a, < 0.4 or q < 2.5) but fall under the predicted curve at higher water contents (see fig. 4), in agreement with results already reported for the homoionic systems and other ion-exchange systems. 2*H. R. Corti 3253 2 80 24 0 - -.( I : 2 200 E I I I 1 0 4 6 8 10 4 Fig.1. Equivalent volume of Na-CsPSS at 298 K as a function of the swelling variable q. 0, y , = 0.000; A, y , = 0.148; 0, y , = 0.391 ; V, y , = 0.702; 0, y = 0.861 ; values from ref. (3): 0, y , = 0.000; +, y , = 1.000. In the inset the values of &(a), (q = 0) (b) and F/p ( c ) are shown as a function of the ionic composition. Table 3. Partial molar volume of water and heteroionic polyelectrolyte Y , 2 < q < 2 0 q > 20 0.000 139.2 130.6f0.8 17.34f0.16 126.2f5.3 18.056f0.004 0.148 135.7 129.7f0.5 17.53f0.13 120.7f 1.3 18.059f0.003 0.391 141.7 135.2f0.5 17.02f0.12 132.4f2.9 18.062&0.011 0.702 151.1 143.9f0.2 16.97f0.04 153.1 f 10.3 18.036f0.004 0.861 156.1 149.2f0.7 17.83f0.16 159.9f8.8 18.077f0.009 1.000 (161) (155) (1 7.9) - (134.7)" (127.7) (1 7.7) (121.7) (18.07) aValues in parentheses are from ref.(3). The linearized B.E.T. equation12 is given by 1 ( c - l ) a , a, =-+- (1-ao)q qrnc q m c where q, = no/np in the first hydration 'layer' and c = exp (El - E,)/RT3254 Thermodynamic Properties of Polyelec tr oly te Solu t ions 1.15 1.10 m I 5 80 P \ 1.05 1.00, 0 0.5 1 .o C"/mol dm-3 1.5 Fig. 2. Density of dilute Na-CsPSS solutions at 298 K (symbols as in fig. 1). Inset: values of A' [eqn (13)] and T/p(q = 0). 12 10 8 4 6 2 0 0.5 QO 1.0 0 0.5 Y2 1.0 Fig. 3. (a) Water sorption isotherm of Na-CsPSS at 298 K; (6) swelling variable as a function of the ionic composition a, values from 0.0703 (lowest curve) up to 0.9019 (upper curve) (symbols as in fig.1).H . R. Corti 3255 1.5 w i !. 4 1.0 Q. n U I 0 c1 w . 0 c3 0.5 0 0.5 1. 0 a0 Fig. 4. B.E.T. isotherms for Na-CsPSS at 298 K. Inset: ( E , - E , ) in kcal mol-' and q, as a function of the ionic composition (symbols as in fig. 1). 0 0.5 1.0 a0 Fig. 5. 4-l us. a, for Na-CsPSS at 298 K (symbois as fig. 1). in which El and EL are the absorption energy in the first layer and the solvent condensation energy, respectively. This equation applied to our systems for 0 < a, < 0.4 yields the excess energy, El - EL, independent of the ionic composition (2.1-2.2 kcal mol-l) in spite of the fact that q, decreases from 1.55 to 1.21 as y z rises from 0 to 0.86. Hence qm seems to be associated with the counterion size, since a large counterion linked3256 Thermodynamic Properties of Polyelectrolyte Solutions 8 ' I I I I .I I I I I I I 0 2 4 6 8 10 4 0.5 1 .o l / q Fig.6. Free enthalpy of hydration for Na-CsPSS at 298 K as a function of q (a) and q-' (b) (symbols as in fig. 1). to a fixed charge on the polymer chain prevents water molecules from reaching these specific sorption sites. At very low water uptakes there are two different states of hydration. The first water molecules fill the 'free' space between polymeric chains and strongly interact with mobile and fixed charges. If more water molecules are added to the system the counterions are separated from the polyanion chain and a second region of counterion hydration emerges. The transition from the first to the second region daes not occur at q = 2-3 as has been ~uggested,~ but rather around q = 1 (cf.fig. 1). Some empirical relationships may be used to correlate a,, and q. Thus a linear relation exists between a,, and q-l for a, > 0.3, as shown in fig. 5. This relationship has been obtained13 by a B.E.T. procedure when multilayer adsorption predominates, subtracting the monolayer volume and assuming a single-value energy for other layers. The resulting isotherm is given by 4-l = qkl( 1 - ka,,) where k is a constant associated with the heat of adsorption. Eqn (16) has been used13 to analyse water sorption on oxide surfaces at a, > 0.2. Using this type of isotherm it was possible to extrapolate the q values for the pure caesium resin ( y , = l), in good agreement with previous results for CSPSS.~ The inverse of q is related to &, the volume fraction of polymer that is often used in connection with the tortuosity effect on the ion mobility,' in a simple way: The free enthalpy for the swelling process was calculated from eqn (8) using the water- sorption results.The results for NaPSS-CsPSS are shown in fig. 6(a) as a function of q and in fig. 6(6) as a function of q-l. AGh may be written as the sum of a configurational and an electrostatic term. TheH. R. Corti 3257 I 1 0 0.5 1.0 Y2 Fig. 7. Equivalent volume of Na-CsPSS at 298 K as a function of the ionic composition at fixed values of q (symbols as in fig. 1). former is the contribution of the mixture process and the change in the conformation of the polymer chain during hydration. This term depends on &, and it is reasonable to assume that it reaches a constant value (0.8-1 .O kcal mol-l) in linear polyelectrolytes for q > 2, i.e.when the swelling pressure is not too large. The electrostatic effect involves interactions among mobile and fixed ions and solvent dipoles. For q > 3 the electrostatic interaction involves water molecules out of the primary hydration layer and its contribution to AGh reaches a constant value. The dramatic change in AGh for 0 < q < 2 is due to strong interactions with the first water molecules which polarize the metal sulphonic group binding, promoting the formation of hydrated species and large changes in the polymeric conformation. There is a change in the slope of the AG vs. q-l curves for the Na-CsPSS systems at q = 2 [cf.fig. 6(b)] which is more evident in the caesium-rich systems. The behaviour of the water uptake and equivalent volume with ionic composition is complex. At y , > 0.40 the isotherms lie on a common curve; the same occurs for V at y2 < 0.40, with a shallow minimum at y , z 0.15 (cf. table 3). 6 for NaPSS decreases by > 10 cm3 mol-1 when the first molecule of water is sorbed for the dry polyelectrolyte, indicating a large ‘free’ volume at q = 0. If sodium is replaced by caesium, a reorganization of the polymer chains takes place in such a way that the free volume diminishes. At higher caesium content the larger size of this ion predominates and I/ increases with y,. At high q values the sodium ion is more hydrated then caesium, and the minimum in the Y us.y2 curve disappears, as shown in fig. 7. That explanation is supported by the behaviour of the sorption isotherms. At y2 > 0.40 an overlapping of isotherms is found, because at high caesium contents the mean distance between polymer chains increases in view of the large caesium size, enhancing the water sorption. This effect is3258 Thermodynamic Properties of Polyelectrolyte Solutions counterbalanced by the lower caesium ion hydration. A similar pattern was observed in Zeo-Karb resins with sodium and caesium counterions. l4 Finally, it is important to point out that some spectroscopic studies have ~ h o w n l ~ . ~ ~ that large ions such as caesium can build lattice-like structures in the polyelectrolyte matrix when fixed charges on it are separated at situable distances.A large ion would interact with a number of fixed charges simultaneously. This fact has a great effect on changes in the transport properties of the heteroionic systems with the ionic composition. l7 Conclusions The thermodynamic behaviour of heteroionic polyelectrolyte solutions is far from ideal and it is largely determined by differences in counterion sizes and their interactions with fixed charges on the matrix and with solvent molecules. The water sorption isotherms obey the B.E.T. equation only in the concentrated region (a, < 0.4), but a modified B.E.T. equation can be used for dilute solutions (up to a,, z 0.9) in such a way that the entire range of concentration studied in this work is well described. The thermodynamic properties of Na-CsPSS solutions show unusual behaviour in the sodium-rich region (0 < y z < 0.25) where the equivalent volume changes little with the ionic composition.This is probably related to the appearance of a lattice-like structure promoted by the caesium ion. References I B. R. Sundheim, M. H. Waxman and H. P. Gregor, J. Phys. Chem., 1953, 57, 974. 2 M. H. Waxman, B. R. Sundheim and H. P. Gregor, J . Phys. Chem., 1953, 57, 969. 3 E. 0. Timmermann, Z . Phys. Chem. N.F., 1970, 72, 140. 4 H. P. Gregor, B. R. Sundheim, K. M. Held and M. H. Waxman, J. Colloid Sci., 1952, 7, 51 1. 5 H. P. Gregor, F. Gutoff and J. I. Bregman, J . Colloid Sci., 1951, 6, 245. 6 A. E. Lagos and J. A. Kitchener, Trans. Furaday Soc., 1960, 56, 1245. 7 R. Fernandez Prini and M. Philipp, J . Phys. Chem., 1976, 80, 2041. 8 E. 0. Timmermann, J . Chem. SOC., Faraday Trans. 1 , 1982, 78, 2619. 9 D. G. Dickel, H. Degenhart, K. Hass and J. W. Hartmann, 2. Phys. Chem. N.F., 1959, 20, 121. 10 R. A. Robinson and R. H. Stokes, Electrolyte Solutions (Butterworths, London, 1959). 11 R. Fernindez Prini, Thesis (University of Buenos Aires, 1962). 12 S. Brunauer, The Adsorption of Gases and Vapours: Physical Adsorption (Princeton University Press, 13 A. C. Zettlemoyer, F. J. Micale and K. Klier, in Water: A Comprehensive Treatise, ed. F. Franks 14 P. Meares and J. F. Thain, J, Phys. Chem., 1968, 72, 2789. 15 G. Zundel, Hydration and Intermolecular Interaction (Academic Press, New York, 1969). 16 L. Y. Levy, A. Jenard and H. D. Hurwitz, J. Chem. Soc., Faraday Trans. I , 1980, 76, 2558. 17 H. R. Corti, J . Chem. Soc., Faraday Trans. I , 1987, 83, 3259. Princeton, 1945). (Plenum Press, New York, 1977), vol. V, chap. 5. Paper 6/1060; Received 28th May, 1986.

ISSN:0300-9599    

DOI:10.1039/F19878303249

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J. Chem. SOC., Faraday Trans. 1 , 1987, 83 (1 I), 3259-3270 Transport Phenomena in Concentrated Aqueous Solutions of Sodium-Caesium Polystyrene Sulphonates Horacio R. Corti Departamento de Quimica Inorganica, Analitica y Quimica Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pahellon 2, Ciudad Universitaria, Nuiiez, Cap. Federal, Argentina The electrical conductivity, intradiffusion coefficients and ionic con- ductivities of sodium and caesium ions have been measured for polystyrene sulphonates in their heteroionic forms as a function of q, the number of water molecules per ionic group, at 298.15 K using a novel electrodiffusion technique. The trace diffusion coefficient and ionic conductivity of the chloride ion are also reported. The behaviour of the transport properties as a function of the water content and the ionic composition are analysed.The empirical relationships valid in homoionic sulphonic ion-exchangers hold in the heteroionic systems. Some anomalies are found in the sodium-rich region as a consequence of the formation of a lattice-like structure involving caesium ions. The counterion mobilities increase with the caesium content in the system, as found in ion-exchange membranes and electrolyte solutions. The ratio between electrical and diffusional mobilities of counterions follows the same trends observed in crosslinked ion-exchange systems and mixed electrolyte solutions, indicating that the polymer has a second-order effect. Most ion-exchange systems of practical application are in equilibrium with multi- component electrolyte solutions.In spite of this, experimental information on the transport properties of such systems is restricted to the simple cases of homoionic ion- exchange materials in water or in equilibrium with aqueous solutions containing a single electrolyte.'T2 Only Meares et al.3-7 have made a comprehensive study of phenol- sulphonic membranes (Zeo-Karb 315) in the heteroionic forms Na-Cs and Na-Sr with bromide as coion. The results show us that the pattern of behaviour for the transport properties cannot be directly obtained from the known properties of the pure homoionic systems by using simple addition rules. Moreover, even in mixtures of electrolytes such as NaCl -KCI- H 2 0 and NaClLCsCl -H,O, the ionic mobilities are complicated functions of the ionic composition and total concentration.8 The purpose of this work is to describe a detailed study of the transport properties of polyestyrene sulphonate solutions in the heteroionic form Na-Cs, whose thermodynamic properties have been reported in the previous article.We have chosen this linear polyelectrolyte because it is fully miscible in water, and so it is possible to investigate the nature of the ion transport in the as yet uninvestigated range of very concentrated solutions. This might be taken as a model for describing the behaviour of highly cross- linked or grafted ion exchangers with low water contents. Intradiffusion coefficients for sodium, caesium and other counterions have been reported for this polyelectrolyte in dilute and concentrated solutions2 of the homoionic form.A novel feature of the present study is the use of an electrodiffusion technique for obtaining the intradiffusion coefficient and the electrical mobility of counterions and/or coions simultaneously. 108 3259 F A R I3260 Transport Phenomena in Polyelectrolyte Solutions It is worthwhile to correlate these phenomenological transport quantities with the composition variables and to compare them with the same quantities for the pure homoionic systems. Experimental Materials The preparation and composition of PSSNa-PSSCs mixtures has been described elsewhereg together with details of the water uptake and densities of the solutions used in this work. Electrical Conductivity The strip-shaped samples were prepared on Lucite matrices and the water content was adjusted by isopiestic equilibration with saturated so1utions.l' The modified Kitchener method," using five fixed electrodes, has been described previously.12 The specific conductivity is given by K = pL2Xp/Rmp where p is the density, L the length of the sample, mp its dried weight, R its electrical resistance and x p = rnp/(rnp+m,) the mass fraction of polyelectrolyte in the sample (m, is the mass of water in the sample).The equivalent conductivity is A = K P = L2M/Rm, (2) where Y o is the equivalent volume of the polyelectrolyte solution and A? is the equivalent mass of the salt mixture. A is directly available from the experimental L, R and m,, data.12 No information about water uptake is required. The method was useful up to a water activity of 0.33-0.43 but at lower water contents the strips started to break close to the electrodes.Four samples were measured for each composition and water activity, and the reproducibility was better than 5 % for high water uptake samples but only 10% for concentrated ones. Electrodiffusion In view of the long sample equilibration time and difficulties in reproducing the geometric and thermodynamic characteristics for a given composition and water content, it is desirable to adopt a method for the simultaneous determination of both electrical mobilities and diffusion coefficients of counterions and coions in resins. The electrodiffusion technique described below has been found to be adequate for such a purpose. The strips of resin used in this method were 8 cm in length, prepared on PVC holders plasticized with dinonylphthalate by the same procedure used for those employed in conductivity measurements.Each strip was equilibrated by the isopiestic method for 1-3 months, and while the samples were still fluid, two platinum electrodes were inserted close to their ends. Once the water sorption equilibrium was reached, a track of ca. 1 mm depth and 0.05 mm width was made on both strip and holder with a narrow blade. A small drop (0.2 mm3) of aqueous solution containing the radiotracer was deposited on this track using a microsyringe. The mark of the blade on the PVC matrix defined the origin (x = 0) for the electrodiffusion experiment. The samples were rapidly placed in the same vessels used for the conductivity measurements and an electric current was immediately applied from a constant-current source.Runs lengths and current densities across the samples were estimated from the conductivity data and the mean area of the strips (ca. 0.025 cm2) in such a way that theH . R. Corti 326 1 maximum in the radiotracer profile was always found at a distance between 1 and 2 cm from the origin. As the water activity of the solution decreased from 0.925 to 0.5286, the duration of the runs increased from 15 h to 30 days and the current was reduced from 150 to 5 PA. As a consequence of the current flow through the resin, HPSS was formed in the anodic region, and the cathodic region became alkaline. Nevertheless, as in a Hittorf cell, the central part of the sample held its original composition and the current was mainly due to the small counterions.This central region embraced ca. 2.5-3 cm on each side of the seeding point. Once the run was finished, the strip was cut on the holder into several parts, starting from the origin. These portions were immediately weighed and their lengths were measured using the marks left on the PVC holder. Thus the area of each section could be determined and the mean value was used for calculations. Individual sample portions were dissolved in water and their radioactivity levels were measured in order to determine the radiotracer profile along the strip. The radioisotopes used in this work were Na22, Cs13' and C136. The first two are gamma emitters and were measured with an Alfa Nuclear RM-72034 spectrophotometer containing a scintillation crystal of NaI doped with thallium.For C136, a beta emitter, a Geiger-Muller tube was used; the samples were dissolved in water and a thin film was obtained by drying. This film was used for measurements in order to avoid self-absorption effects. The accuracy of the method is similar, for the diffusion coefficients, to that achieved in diffusion experiments.2 For electrical mobilities errors are often slightly greater, since additional parameters are involved. Under the experimental conditions, chemical and electrical forces act on the ions in such a way that the flow of an species i with charge zi is given by z. Ji = - Di grad ci - 3 wui ci grad q5 zi (3) where ui is the electrical mobility, Di is the diffusion coefficient, q5 is the electrical potential and the subscript w indicates the velocity of the reference system.In our case the flows are measured with respect to the cell, and we term this system CFRS (cell-fixed reference system). By using the continuity condition and the assumption of a constant electrical field, the following equation may be written : ac, a2c. ac . - = D i 2 - - ( v . - w ) at ax2 ax (4) where vi is the velocity of species i. form of the Fick's second law by the Furth's substitution,13 defined by This equation, known as Weber's generalized equation, can be reduced to the usual with vi = v,. - w. ci = Ciexp (;; $) 0ur"electrodiffusion experiments correspond to an infinitely narrow source in x = 0, t = 0, and the solution of eqn (4) becomes where and Mi = p" ci(x, t)dx.108-23262 Transport Phenomena in Polyelectrolyte Solutions In practice, a radiotracer of species i was sown at x = 0 and, after a time t, the strip was cut in N sections and their radioactivity levels, mi, were measured. The fraction f,, defined by n C mj LV C mj f, = I+; M~ = C m j (7) j - 1 j= 1 was then calculated, and by using eqn (6a) we obtained +( 1 + erf y,); y , < 0 1 $(l -erfy,); yn < 0. (8) 1 f n = @ I : C(X, t ) dx = where erf is the error function. Thus the value of y , was found for each section by using eqn (6b), and when the y , values were plotted as a function of x,, D, and u, could be obtained from the slope and the ordinate at x, = 0, as shown in fig. 1. Finally, the electrical mobility was calculated from vi and the electrical field across the sample.Results The specific and equivalent conductivity of sodium ( 1)xaesium (2) pol yestyrene sulphonate solutions as a function of the water content and ionic composition are shown in table 1. If they are analysed at constant q a clear dependence on the ionic composition is found. The higher the caesium fraction in the mixture, the higher the conductivity of the solution, at least for q > 3. However, no difference exists among samples with caesium-ion fractions > 0.7. For q < 3 the conductivity curves tend to join up as shown in fig. 2. In table 2 the intradiffusion coefficients and electrical mobilities for the sodium and caesium counterions and the tracer diffusion coefficient of the chloride coion are summarized. Although the scatter in the experimental data is higher than for the equivalent conductivity, the shapes of the Di and Izi us.q curves are very similar to those shown above for the electrical conductivity, with the caesium and sodium ion mobilities increasing with the caesium content of the solutions. In table 2 the diffusion coefficient for the chloride ion is also given. The electrical mobility is very low or even negative (with migration towards the cathode) as a consequence of the solvent electro-osmotic flow. Discussion Owing to the scatter of the experimental transport coefficients it would be worthwhile to smooth their composition dependence. The relationships previously found in homoionic systems2. l4 between the transport coefficients and the water activity a,, In Xi = a’+b‘a, (9) where a’ and b’ are constants and Xi = Ai or D,, are also valid for heteroionic systems.However, the standard deviation of the coefficients obtained by fitting eqn (9) is lower if q-l, the inverse of the swelling variable,’ is used as a composition variable rather than a,. A linear relationship exists between these variables’ in the range of water activities studied in this work (0.3300 < a, < 0.9248). The coefficients a and b of the related (10) equation, In Xi = a+bq-’ are shown in fig. 3 for the five transport properties studied here. For some of them, a and b change linearly with the ionic composition of the system; nevertheless, someH. R. Corti 3263 - 2 Fig. 1. Electrodiffusion patterns for sodium and caesium counterions at uo = 0.9019.Symbols: 0, y 2 = 0.000; 0, 0.148; 0 , 0.391; U, 0.702; A, 0.861. Table 1. Specific and equivalent conductivity of Na-CsPSS at 298.15 K Y2 a0 0.000 0.148 0.39 1 0.702 0.86 1 0.510 1 Y 3 1.8 & 0.Y" 8.76 & 0.23 0.807 1 16.85 k 0.35 3.91 k0.07 0.7083 9.74 k 0.14 2.0 1 f 0.03 0.6 183 5.71 f0.17 1.10 f 0.03 0.5286 2.2 0.5 0.40 & 0.10 0.4276 3.5 k0.9 0.61 & 0.17 0.3300 1.01 f0.16 0.17 & 0.04 31.8kU.Y 8.25 f0.23 16.6 k0.5 3.63 & 0.10 8.20? 0.25 I .62 & 0.05 - - 1.47 f 0.50 0.26 f 0.05 1.90 k 0.05 0.326 f 0.008 0.283 & 0.01 5 0.046 f 0.003 35.3 k0.8 8.98 f 0.20 15.9 5 0.4 3.45 & 0.10 7.99 f 0. I5 1.57 k 0.03 3.3 k 0.4 0.6 1 f 0.07 1.65 f 0.15 0.29 & 0.04 ._ - - - 41.~7f 1.3 10.8 f0.4 17.8 & 1.2 3.91 k0.26 7.8 f 0.5 l.58kO.I 1 4.47 k 0.21 0.86 f 0.04 1.26 f 0.02 0.230 & 0.004 0.96 5 0.16 0.17 k 0.03 0.23 1 f 0.004 0.040 & 0.00 1 41.3f l.U 11.2f0.3 17.9 & 0.4 4.09 & 0.08 8.88 k0.23 1.87 & 0.05 3.57 k0.07 0.71 1 f0.014 1.44 f 0.2 1 0.27 k 0.05 1.21 50.16 0.23 f 0.03 0.28 f 0.05 0.051 f0.008 a Upper values are K / I O - ~ R-' cm-'; lower values are A/cm2 R-I mol-'.3264 Transport Phenomena in Polyelectrolyte Solutions 2 4 6 8 9 Fig.2. Equivalent conductivity in Na-CsPSS solutions at 298.15 K as a function of the swelling variable. Symbols as in fig. 1. erratic points prevent us from generalizing these results. For this reason the transport coefficients were finally smoothed using only their behaviour with respect to the water content, as expressed by eqn (10).An interpretation of eqn (9) or (10) in terms of the absolute rate theory has been given.", l6 It assumes that the transport process involves an activated ion jumping through the resin with a jump length independent of the water content and an energy barrier related to the free energy of the hydration process, AGh: xi = Kexp ( -RT) AGh where K is a constant which includes the jump distance. In the Na-CsPSS system, the free energy of hydration changes linearly with q-l over this range of water uptake, as has been reported el~ewhere,~ which leads easily to eqn (10) if such a dependence on AGh is introduced into eqn (I 1). Other composition variables such as the volume fraction of polymer have also been used'' to correlate transport coefficients and water content, but it was noted9 that these cornposition variables are linearly related in ion-exchanger systems. The behaviour of smoothed ili and Di values with the ionic composition at constant values of q is shown in fig.4. At high water content the transport coefficients increase with the caesium content of the system, except for the diffusion coefficients at y , > 0.80. At water contents lower than those shown in fig. 4, this behaviour is reversed. The ionic conductivities shown in fig. 4 were measured in a reference system fixed toH. R. Corti 3265 00 0 8 x +I v, m 00 3 0 M r - 3 0 0 0 0 0 m m m 2 0 I +I I +I +I +I I I +I r= 8 m o x m 9 ?99 m '?*o 3 z 0 - , 8 , , 8 , 2 m m o 0 0 m 8 +I 2 8 +I v, 0 8 +I m 8 +I * 8 +I 00 8 +I s 8 +I 2 8 +I m 0 0 0 0 0 8 8 +I I +I v, 8 +I 3 8 +I m 8 +I 2 +I 8 m * 0 0 8 8 +I +I m o m r - w m 3 0 0 0 0 9 9 9 8 8 +I +I +I I +I +I v, m 0 00 F 9 +I 2 * 8 2 +I CI P 8 2 +I - 2 m g 2 v,*m 979 8 8 8 8 +I +I +I I +I I +I +I +I 0 0 0 m P- 8 * m 0 9 v, - m * m - O O m b * m 0 0 0 0 0 0 0 9999999 2 8 8 +I w r- +I I +I I +I +I +I +I +I +I +I I +I +I +I +I +I +I +I +I m w o 0 0 ~ 0000Ob o m m m o r - m m m c n - - 00000 00 2 0 B 8 8 +I F v, I +I +I +I +I +I +I +002?2 wIA00-r-0 ' I G ? \ q w m v , v, v, m m - - v , m r - m - o 8 8 8 8 8 8 8 +I +I +I +I +I +I +I V 3 \o 23266 Transport Phenomena in Polyelectrolyte Solutions Y2 I I , 0 0.5 1 Y2 Fig.3. Coefficients a and b in eqn (10) as a function of the ionic composition.. Symbols: e, IuNa+; ., jl('s+; 0, DNa+; 0, DCs+' 0 0.5 Y2 1 I I 0 0.5 Y2 a 1 Fig.4. Ionic conductivities (CFRS) and intradiffusion coefficients of sodium (0) and caesium (0) ions in Na-CsPSS at 298.15 K as a function of the ionic composition (at fixed values of g). Filled points were taken from ref. (2). the cell (CFRS), in which the conductivity of the polymer chain is not zero. It is possible to obtain the polyanion conductivity ( A 3 ) from the measured ionic and total equivalent conductivities by means of the equation A3 = A-Ac (12) where Ar2 = Y1Al + Y A (13)H . R. Corti 3267 Table 3. Polyion conductivity in Na CsPSS concentrated solutions (cm2 R-' mol-I)" q y , = 0.000 0.148 0.391 0.702 0.86 1 2 0.045 0.013 0.024 0.056 0.063 3 0.219 0.114 0.149 0.360 0.309 4 0.427 0.332 0.327 0.816 0.529 5 0.583 0.628 0.483 1.250 0.554 6 0.669 0.957 0.590 1.582 0.368 7 0.696 1.292 0.646 1.800 0.009 8 0.678 1.616 0.659 1.93 -0.44 a Values obtained from eqn (12) and the smoothed values of A.A1 and i2. 1 I I 0 0.5 Y 2 0 /' I 7 / / ,' a I / 1 / 0 1 0 0.5 Y2 1 Fig. 5. Electrical and diffusional mobilities of sodium (0) and caesium (0) ions in Na-CsPSS at 298.15 K as a function of the ionic composition (at fixed values of g). Pure caesium values from ref. (2). It can be seen from the L3 values shown in table 3 that the polyion makes a large contribution to the equivalent conductivity, even in the more concentrated solutions where the polymer motion should be strongly hindered. It is likely that the displacement of small sections of the polymer chain is responsible for such values.As a first approximation, A3 depends on 4-l in the same manner as the sodium and caesium conductivities. A3 values were plotted as a function of 4-l [eqn (lo)], and the smoothed conductivities of the polyion were used to calculate the ionic conductivities of the counterions in the matrix-fixed reference system (MFRS) by using the relationship (14) 312i = Ri + L3.Transport Phenomena in Polyelectrolyte Solutions 0 0 -5 1 Y2 ~ 0 0.5 1 Y z Fig. 6. Electrical and diffusional mobilities of sodium (0) and caesium (0) ions in Zeo Karb membranes immersed in NaBr-CsBr solutions of concentrations 0.1 and 0.02 mol dm-3.4,5 In order to compare the electrical and diffusional mobilities of the counterions, the smoothed values of &F2 and DJRT as a function of the ionic composition at constant values of q are shown in fig.5. The mobilities of both sodium and caesium increase with the caesium content for q > 3, i.e. in the region where the counterions are normally hydrated. Thus the mobility of poorly hydrated caesium ions in solutions containing strongly hydrated sodium ions is lower than in the CsPSS pure homoionic system because caesium ions move in a medium with less free water. The same effect occurs in ternary electrolyte solutions.8 The counterion-solvent interactions are not uniquely responsible for the transport behaviour in heteroionic polyelectrolyte solutions described above. It is also important to consider the interactions of the counterions with the polyion. It has already been mentionedg that caesium ions would be more associated with the matrix than sodium ions.Thus caesium ions are able to shield the fixed charges on the matrix more efficiently, enhancing the sodium mobility with respect to its mobility in pure NaPSS. The final result of the interactions of sodium and caesium ions with water and polymer is an increase in their mobilities as the caesium fraction in the resin increases at constant water uptake. This effect seems to be more marked in the sodium-rich region as a result of the structural changes observed there.g For q < 3 our system has insufficient water to complete the hydration shell of the counterions, and the caesium mobility in CsPSS becomes equal to or even lower than sodium mobility in NaPSS, because in this case it is the crystallographic radii which determine the ion mobility, as happens in ternary molten salts.18 Meares et al.77 l9 have studied the behaviour of phenolsulphonic membranes immersed in NaBr-CsBr solutions.In spite of the higher water uptake of this system and the presence of a small quantity of bromide coion in the system, the variation of the ionic conductivities and diffusion coefficients with the ionic composition resembles that of the Na-CsPSS system in the dilute region (q > 3) as shown in fig. 6. It is not clear why caesium ions are more associated with the fixed negative chargesH . R . Corti 3269 Table 4. Nernst-Einstein factor in Na-CsPSS concentrated solutions q ion y , = 0.000 0.148 0.391 0.702 0.861 4 Na' CS' 5 Na' CS' 6 Na+ CS' 7 Na' CS' 1.59 1.18 1.13 1.76 1.07 1.39 1.08 1.29 1.43 1.69 1.42 1.19 1.22 1.55 1.29 1.39 1.27 1.34 1.47 1.67 1.31 1.20 1.28 1.41 1.45 1.40 1.41 1.38 1.50 1.66 1.24 1.20 1.33 1.32 1.58 1.42 1.53 1.41 1.52 1.66 on the polymer, but spectroscopic studies20*21 suggest that large ions can build lattice- like structures into the polyelectrolyte matrix when the fixed charges on it are separated at suitable distances.A large ion like caesium would interact in such a way with a number of negative charges simultaneously. In order to complete this study the validity of the Nernst-Einstein relationship in this system will be discussed. It is often found that ionic conductivity in ion-exchange materials is estimated from diffusion measurements, in spite of the fact that the is unity only for infinite dilution of all the solution components, a situation of scarce practical interest in this kind of system.It can be seen in fig. 5 that in concentrated Na-CsPSS solutions the electrical mobilities (MFRS) are higher than the diffusional ones, i.e. 3@)i > 1. The values of 3@)i for the heteroionic Na-CsPSS system are listed in table 4. There is a trend for 3@cs to increase with the water uptake and the caesium content of the resin. The behaviour of 3@DNa is not so clear. Chemla et a1.22 and P a t e r s ~ n ~ ~ have found 3@Na values > 1 for sodium homoionic polystyrene sulphonic membranes (Asahi CK 1, C 60N and C 60E). The Nernst-Einstein factors for sodium and caesium in the heteroionic system studied by Meares et aL5 are also > 1 when they are calculated in the MFRS.It is interesting to compare the Nernst-Einstein factor for sodium and caesium in NaPSS and CsPSS with those obtained in 3 mol drn-3 NaCl and CsCl s o l u t i o n ~ . ~ * - ~ ~ In this case QNa = 1.69 in NaCl and mCs = 1.45 in CsC1, where the electrical conductivity of the solution corresponds to the cation conductivity in the chloride-fixed system. It should be concluded that the ionic transport mechanism in ion-exchange membranes and in polyelectrolyte and electrolyte solutions obeys the same fundamental laws, the polymer chain having a secondary effect on these properties. The chloride conductivity is anomalous in this system because it is influenced by a large electro-osmotic water flow. In polyelectrolyte solutions and ion-exchange membranes water is transported by counterions, and consequently it has the same flow direction as theirs.Chloride-ion transport is hindered by water counterflow and their electrical conductivity becomes small or even negative in the CFRS. Differences between diffusional and electrical mobilities of coions could be taken in such systems as an indirect measurement of the electro-osmotic flow of the solvent. There is a lack of experimental information on the solvent electro-osmotic flow which prevents analysis of the transport properties in a solvent-fixed reference system. However, an assessmentf6 of the solvent transport based on the reduction of the coion electrical mobility would indicate that the water mobility is very close to the counterion3270 Transport Phenomena in Polyelectrolyte Solutions mobility, i.e.most of the water molecules in the system form part of the hydration shell of the counterion and they are involved in the transport process. Moreover, the electrosmotic flow of solvent in concentrated polyelectrolyte solutions is very similar to those reported in crosslinked sulphonic membranes23 for the same water content. An assessment of 3'0 is possible through the equation: where the chloride conductivity in the solvent-fixed reference system is replaced by the diffusional mobility using a Nernst-Einstein factor of 1.3.23 Thus, the values of 3zo are 0.73 and 3.6 mol Faraday-' for q = 2.15 and 4.37, respectively, in good agreement with values for C60E and C60N membranes. At higher water uptakes the flow of solvent in the linear polyelectrolyte seems to be higher than in crosslinked membranes as a consequence of steric factors.Conclusions The electrodiffusion technique employed in this work seems to be a powerful tool for obtaining direct information on the diffusional and electrical mobilities of counterions and coions in concentrated polyelectrolyte solutions. In spite of the large contribution of the polyion to the total conductivity, the transport of small ions in this system seems to be similar to the ionic transport in ion-exchange membranes and concentrated aqueous electrolyte solutions. For all these systems the mobilities of sodium and caesium in a mixture of both increase with the caesium fraction, and the Nernst-Einstein factor is higher than unity in the MFRS. Thus the presence of a macroion plays only a secondary role and would be well represented by a tortuosi t y-effect factor.References 1 C. McCullan and R. Paterson, J . Chem. SOC., Faraday Trans. I , 1973, 69, 2113. 2 E. 0. Timmermann, 2. Phys. Chem. N.F., 1970, 70, 195. 3 P. Meares and J. F. Thain, J. Phys. Chem., 1968, 12, 2789. 4 P. Meares and A. H. Sutton, J . Colloid Interface Sci., 1968, 28, 118. 5 P. Meares, W. J. McHardy and J. F. Thain, J . Electrochem SOC., 1969, 116, 920. 6 P. Meares, W. J. McHardy and A. H. Sutton and J. F. Thain, J . Colloid Interface Sci., 1969, 29, 7 P. Meares, T. Foley and J. Klinowski, Proc. R. SOC. London, Ser. A, 1974, 336, 327. 8 E. 0. Timmermann, Ber. Bunsenges. Phys. Chem., 1979, 83, 263. 9 H. R. Corti, J . Chem. SOC., Faraday Trans. I , 1987, 83, 3249. 10 R. A. Robinson and R. H . Stokes, Electrolyte Solutions (Butterworths, London, 1959). 11 G. J. Hills, A. 0. Jakubovic and J. A. Kitchener, J . Polym. Sci., 1956, 19, 382. 12 E. 0. Timmermann, Thesis (University o f Buenos Aires, 1968). 13 S . Lengyel, Z. Phys. Chem. (Liepzig), 1965, 228, 393. 14 E. 0. Timmermann, J . Chem. SOC., Faraday Trans. I , 1982, 78, 2619. 15 C. S. Fadley and R. A. Wallace, J . Electrochem. SOC., 1968, 115, 1264. 16 H . R. Corti, Thesis (University of Buenos Aires, 1980). 17 R. Fernandez Prini and M. Philipp, J. Phys. Chem., 1976, 80, 2041. 18 I. 0. Kada, R. Tagaki and K . Kamamura, Z. Naturforsch., Teil A, 1979, 34, 498. 19 T. Foley and P. Meares, J . Chem. SOC., Faraday Trans. I , 1976, 72, 1105. 20 G. Zundel, Hydration and Intermolecular Interactions (Academic Press, New York, 1969), chap. IV. 21 L. Y. Levy, A. Jenard and H. D. Hurwitz, J. Chem. SOC., Faraday Trans. I , 1980, 76, 2558. 22 M. Chemla, A. M. Poiteau and Y . Prigent, J . Chim. Phys., 1975, 72, 57. 23 R. Paterson and C. Gardner, J . Chem. SOC. A, 1971, 2254. 24 R. Paterson and J. Anderson, J. Chem. SOC., Faraday Trans. I , 1975, 71, 1335. 25 D. J. Miller, J . Phys. Chem., 1966, 70, 2639. 26 R. Paterson, H. S . Dunsmore and S. K . Jalota, J . Chem. SOC. A, 1969, 1061. 116. Paper 611059; Received 28th May, 1986

ISSN:0300-9599    

DOI:10.1039/F19878303259

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J . Chern. Soc., Faraday Trans. I , 1987, 83 ( l l ) , 3271-3282 Hydrazine Reduction of Transition-metal Oxides Donald M. Littrell, Daniel H. Bowers and Bruce J. Tatarchuk* Department of Chemical Engineering, Auburn University, Alabama 36849, U.S.A. The surface interactions of the thermodynamically stable oxides of the first- row transition metals with hydrazine, N,H,, have been assessed by X-ray photoelectron spectroscopy (X.P.S.), and the observed reactivity explained on the basis of the oxides' thermodynamic and acid-base properties. Microgravimetry, transmission electron microscopy (TEM) and X.P.S. studies of copper(1r) oxide (CuO) reduction by hydrazine indicate morphological changes associated with enhanced reactivity. Comparison of hydrazine and hydrogen reduction treatments shows that CuO reduction by hydrazine is more spontaneous and provides a greater increase in surface area than does hydrogen at similar reaction conditions.The interaction of hydrazine, N,H,, with metal oxides has wide and diverse applications for the microelectronic, electrochemical and aerospace industries. Some transition-metal oxides are known to be easily reduced by hydrazine,1-6 with the resulting formation of safe, non-toxic products : an n aM,O, + bN,H, -+ M,,O,, + bN, + 2bH,O where m' m anm' 0 G 7 < - - and am=-+2b. n n n' Surface analysis during metal oxide reduction by hydrazine has received little attention, although the heterogeneous decomposition of hydrazine on various metals has been extensively studied.'-16 In view of the relative lack of data, surface interactions of hydrazine with the thermodynamically stable oxides of the first-row transition metals were assessed by X- ray photoelectron spectroscopy (X.P.S.) to determine those oxides most easily reduced.An explanation of the resultant reactivity has been suggested based on the thermodynamic, physicochemical and catalytic properties of these oxides. In con- junction, morphological changes which occur during CuO reduction have also been examined using X.P.S., microgravimetric techniques and transmission electron microscopy (TEM). Experimental Equipment X-Ray Photoelectron Spectroscopy All X.p. spectra were obtained using a Leybold-Heraeus PAH 10/ 1 1 spectrometer with A1 Kal,, X-rays (1486.6 eV). The angle of incidence of the photons was 60" off-normal, and the emitted electrons were collected normal to the sample surface except where noted.The base pressure of the system during hydrazine dosage was typically Pa. The spectrometer dispersion constant was set by measurement of the energy difference 327 13272 Hydrazine Reduction of Transition-metal Oxides between the Cu 2p3/2 and Cu 3p3,, lines of a sputter-cleaned copper foil. A polycrystalline gold sample integrated into the sample rod was used to calibrate the spectrometer work function; all binding energies were referenced to the Au 4f,,2 peak at 83.8 eV. The full width at half maximum (f.w.h.m.) of the Au 4f,,a peak at typical spectrometer settings was 0.8 eV. Spectra were digitally collected with a Tracor-Northern 1710 multichannel analyser and stored for future retrieval/analysis.Deconvoluted spectra were fitted with Gaussian peaks by a least-squares procedure. X.P.S. samples were treated with hydrazine in situ using a molecular-beam doser. Hydrazine vapour was introduced into the system through a glass capillary array with 10 pm pores positioned 5 cm from the sample position. The expansion effect of this collimated wave of gas allowed an estimated 100-fold enhancement in hydrazine pressure at the sample, compared to the N,H, background pressure based on flux calculations for cosine-type effusion sources, estimated pumping speeds and known background pressures. A stainless-steel jacket surrounding the array permitted the option of an additional differential pumping stage. Micr ograu ime t r ic Analyses A Cahn 2000 recording microbalance, with a capacity of 1.5 g and an ultimate precision of f0.2 pg, was used in the morphological studies of reduced CuO.A rough pump backed by a liquid-nitrogen trap provided an ultimate pressure capability of 0.07 Pa in the Pyrex vacuum chamber surrounding the balance. Pressures were monitored during B.E.T. isotherms with a Wallace and Tierman pressure gauge accurate to f 340 Pa. Buoyancy effects, measured using helium at 77 K, were corrected to a nitrogen equivalent buoyancy by multiplication of the gas density ratio (NJHe). Buoyancy corrections required during reaction with hydrazine were measured at ambient conditions and corrected in a similar manner. For hydrazine reduction studies in the microbalance, the weight of the oxide was monitored during exposure to ca.560 Pa of hydrazine. A helium carrier gas at 100 kPa was bubbled through a fritted Pyrex dispersion tube located in a bulb of liquid anhydrous hydrazine at 298 K. The partial pressure of the hydrazine was reduced to 560 Pa by dilution of this hydrazine-saturated He stream, with an additional helium stream flowing over the balance assembly. This stream was also used to minimize hydrazine contact with the balance mechanism. Transmission Electron Microscopy Micrographs in the morphological study were taken using a Phillips EM-300 transmission electron microscope at 60 kV beam energy. The background pressure in the microscope was < 5 x lop4 Pa. Samples were treated for 9 h in a Pyrex U-tube reactor at 530 Pa of hydrazine in an analogous method to the gravimetric studies.Note that samples were exposed to atmosphere during loading into the microscope. Some contamination was introduced during TEM examination, as evident from a light haze at specimen surfaces. This contamination was believed to be carbonaceous in nature.17 Materials Hy drazine Technical-grade anhydrous hydrazine ( < 1.5 O h H,O) provided by Olin Chemicals was subjected to alternating freeze-thaw cycles under vacuum for removal of residual non- condensible gases. Mass-spectral analysis'' confirmed the composition of the gas phaseD. M. Littrell, D. H. Bowers and B. J. Tatarchuk 3273 to be predominantly molecular hydrazine ; gas-phase photodecomposition or catalytic decomposition from the leak valve’s copper seal had no significant effect, and contamination of the hydrazine by water was minimal.X . P.S. Specimens Oxides of vanadium, iron, cobalt, nickel, copper and zinc were prepared from polycrystalline metallic foils of 0.1 mm thickness (Johnson-Matthey Chemicals, purity > 99.95 Yo). Oxides of chromium and manganese were prepared from flake materials (Electronic Space Products). All metals were degreased with acetone and methanol before being oxidized in air at appropriate temperatures to form the indicated oxides, (i.e. V205, Cr,03, Mn203, Fe203, Co304, NiO, CuO and ZnO). Evidence for the formation of these species was obtained by (i) comparison of the observed X.p. spectra with those obtained from the literature (V205,19-22 Cr203,19920*22-26 Mn 2 0 3’ 2 2 9 2 6 - 2 9 (ii) comparison of the experimentally observed lattice oxygen to metal atomic ratios with those expected for the appropriate oxide stoichiometry (table 1).These comparisons utilized just that portion of the 0 1s signal associated with lattice oxygen and were corrected for photoionization c ~ o s s - s ~ c ~ ~ ~ ~ s , ~ ~ electron escape depths45 and empirically determined spectrometer efficiency Chromium specimens appeared to exhibit multiple oxidation states : predominantly Cr203 with traces of CrO, and CrO,. Fe203,22, 26,28,30-34 Co,04,22,28,35,36 Ni0,22,32,35,37-40 Cu022,35,37,42,43 and Zn022943) and Micrograuimetric Specimens Only CuO samples were examined during microgravimetric studies ; CuO was prepared from copper wool (fine grade 99.9 YO, Carey Electronics).Sample pretreatment before oxidation included cleaning in trichloroethane and acetone to remove organics and subsequent placement in vacuum (0.1 Pa) for 1 h at 298 K to remove adsorbed species. The copper was prereduced in hydrogen at 673 K for 8 h at 100 kPa. Oxygen was removed from the hydrogen stream using, in series, a commercial hydrogen purifier (Deoxo, Fischer Scientific), a copper turnings trap at 523 K and 5X molecular sieves at 77 K. Copper was subsequently oxidized in oxygen (99.99 O h ) at 723-773 K and 100 kPa for 15-60 h depending on the desired scale thickness. These conditions are appropriate for formation of 75-100 % Cu0.47948 The temperature was increased from room temperature to reaction temperature (723 K) at the rate of 100 K h-l.Transmission Elect yon Microscopy Specimens Copper grids (Balzar Union) used in TEM studies are pre-reduced and oxidized in a manner similar to samples prepared for microgravimetric studies. Results and Discussion Thermodynamic Considerations Reactivity of an oxide in hydrazine is based on both kinetic and thermodynamic driving forces. Identification of those oxides most easily reduced by hydrazine was determined by subjecting each oxide to a standard hydrazine treatment in the X.P.S. apparatus: an in situ dose for 30 min at a surface N,H4 pressure of ca. 6.7 Pa using the molecular-beam doser.3274 Hydrazine Reduction of Transition-metal Oxides Table 1. Reducibility of transition-metal oxides in hydrazine" oxygen : metalb reducibility metal experimental theoretical metal oxide factor (R)" V Cr Mn Fe c o Ni c u Zn 2.80 1.32 1.46 1.28 1.08 0.98 0.98 d - 2.50 1 S O 1 S O 1 S O 1.33 1 .oo 1 .oo 1 .oo 0.97 CrO,, CrO, 0.90 0.98 0.99 coio, 0.90 NiO 0.94 CUO 0.05 ZnO 0.95 a Operating conditions : 30 min at 295 K, 6.7 Pa at the sample surface.Lattice oxygen to metal ratio corrected for photoionization cross-sections, electron escape depth and analyser efficiency ; accuracy estimated at 20 %. R = (oxygen : metal) after reduction/oxygen : metal) of the oxidized precursor; includes all observable oxygen species. An elevated 0 : C r ratio results from contamination of the Cr20, with CrO, and CrO,; the 0xygen:metal ratio was not attempted due to the complexity of deconvoluting the 0 1s spectrum. A reducibility factor (R), defined as the oxygen-to-metal ratio of the reduced sample divided by the oxygen-to-metal ratio of the oxidized sample, was used to compare the relative ease of reduction for each oxide (table 1).The reducibility measurement was based on all types of oxygen observed by X.P.S., including contributions from lattice oxygen, hydroxyl species, adsorbed water and carbonyl species. Of the specimens examined, CuO was the most easily reduced (lowest R), losing 95 YO of its initial oxygen content following hydrazine treatment. The nature of oxygen species at the surface is important when considering oxide- N2H4 interactions. The 0 1s photoelectron spectrum of CuO (fig. 1) exhibited multiple oxygen species identified as : (i) lattice 3 5 y 3 7 3 42 at 530 eV, (ii) surface hydroxyl specie^*^-^^ at 531.6 eV and (iii) adsorbed waters0ys2 at 533.5 eV.Water is known to desorb at room temperature, whereas contamination by carbon-containing species may contribute to the peak at 533.5 eV.31 The peak corresponding to surface OH groups was observed in the 0 1s spectra of all transition-metal oxides examined in this study; the position of this peak (531.61 0.2 eV) was independent of the oxide studied, since the contribution to the potential of the inner shell of oxygen from the proton in the OH group over-rides the influence of the cation.49 Although the lattice-oxygen component of CuO was removed by thermal reduction at 325 K, in agreement with the Cu-0 phase diagram,47 the peak assigned to the hydroxyl species remained essentially unchanged at temperatures up to 450 K.Previous have reported the presence of these strongly chemisorbed OH groups on CuO at temperatures approaching 775 K. A decrease in intensity of both lattice and hydroxyl oxygen was noted upon hydrazine exposure (fig. 2). Subsequent deconvolution of the 0 1s spectra showed an increase in the relative proportion of hydroxyl to lattice oxygen, suggesting preferential removal of lattice oxygen and/or generation of surface hydroxyl species resulting from water formation in the N2H4-oxide reaction. Hydrogen abstraction from adsorbates by chemisorbed oxygen has been the subject of previous inve~tigations.~~9 53-55 X.P.S. studiesso* 55 have confirmed the formation of surface hydroxyl species resulting from these reactions. These hydroxyl groups subsequently dehydroxylate through the desorption of 55 Roberts et a1.l'.543275 543 5 2 3 binding energy/eV Fig. 1. Deconvolution of the 0 Is spectrum of CuO. Species identification: (1) 530 eV, lattice oxygen; (2) 531.5 eV, surface hydroxyl species; (3) 533.5 eV, chemisorbed oxygen-containing species. 54 3 523 binding energyfev Fig. 2 . 0 1s spectra of CuO with increasing exposure to hydrazine : (a) oxidized sample, (b) 50, ( c ) 500 ( d ) 3000 and (e) > 50000 laiigniuir N,H, (1 langmuir = Torr s).3276 Hydrazine Reduction of Transition- metal Oxides suggest that strong hydrogen-oxygen bonding provides the kinetic driving force for oxygen-induced chemisorption of hydrogen donors ; the thermodynamic driving force being primarily dependent upon the formation of water. The CuO-N,H, system investigated here may parallel the oxidized copper-NH, reaction reported by Matloob and Roberts." The kinetic driving force for the dissociation of the N-H bonds results from strong hydrogen-oxygen bonding.This interaction results in an increase in adsorption energy of the adsorbate and a corresponding decrease in the activation energy for the dissociation of the N-H bond." The ease of reducibility of CuO may be attributed to its relative thermodynamic and kinetic instability in comparison with the other oxides examined. These oxides exhibited a monotonic increase in their relative ease of reduction us. the heat of formation of the oxide per mole of oxygen (i.e. -AH& per mole of oxygen) as shown in fig. 3.This type of correlation is indicative of a relationship between bulk and surface heats of f o ~ m a t i o n ~ ~ . ~ ~ and has been widely used to qualitatively predict the relative rates of surface reaction^.^*-^' the greater reactivity of Ni oxide over Fe oxide with -NH, groups of ethylenediamine, NH,CH,CH,NH,, was also rationalized on the basis of the oxide's thermodynamic stability (i.e. oxide heat of formation). Ethylenediamine dissociatively adsorbs on metallic iron and nickel to form NH,CH,CH,NH-* at 300 K. Preoxidation of iron inhibits dissociative adsorption at oxygen coverages below half a monolayer, resulting in largely molecular adsorption. In contrast, nickel surfaces with similar oxygen levels still provide dissociative adsorption sites for ethylenediamine with removal of surface oxygen in the sequence shown below: In a similar NH,CH,CH,NH,(g) + 2* 3 NH,CH,CH,NH-* + H-* (2) 2H-* + 0-* -+ H,O(g) + 3*.(3) In this process oxygen vacancies are required to remove a hydrogen atom during dissociative adsorption [reaction (2)] and the subsequent scavenging of surface oxygen [reaction (3)] has an autocatalytic effect from the resulting production of oxygen vacancies. Evidence for this is provided by the predominantly molecular adsorption of ethylenediamine on nickel oxide at saturated coverages, indicating that the -NH, proton is inactive toward the nickel oxide surface and requires oxygen vacancies to promote dissociative adsorption. The molecular processes governing the reaction with oxidized iron are quite different from that on nickel; surface oxygen on iron is less reactive with a weak acid such as ethylenediamine, and dissociative adsorption is not observed on iron surfaces which are partially covered with oxygen. The basis for this phenomenon may result from the relative ease with which an iron surface forms an oxide through the interaction with water at low pressure and room temperature, owing to the much larger heat of formation of iron oxide than that of nickel oxide.The reduction reaction of oxides with relatively small heats of formation (e.g. CuO and Cu,O) by -NH, groups (i.e. hydrazine) may be self-propagating from the resulting formation of metallic sites adjacent to chemisorbed or lattice oxygen. The low degree of reduction exhibited by the majority of the transition-metal oxides examined here may be due to surface kinetic limitations at the temperatures and pressures of this study rather than the respective driving force provided by surface thermodynamics.Acid-Base Interactions Although the high reactivity of CuO might be expected on the basis of thermochemical properties, the CuO/N,H, reaction may also be considered in terms of acid-baseD. M. Littrefl, D . H . Bowers and B. J . Tatarchuk 3277 1.2 1.0 0.8 R 0.6 0.4 0.2 0 Q CUO ~~ 3 375 -AH& per mol oxygen/kJ mol-I Fig. 3. Reduction of first-row transition-metal oxides in hydrazine. Reducibility factor = (oxygen : metal) reduced/ (oxygen : metal) oxidized precursor. Reducing conditions : 6.7 Pa hydrazine at 295 K for 30 min. interactions. Hydrazine decomposes upon adsorption to metal surfaces through the formation and interaction of free radical^.^ One step in this decomposition involves formation of bonds between the nitrogen atoms in hydrazine and the incomplete d orbitals of the Although no simple correlation has been found between electronic structure and reactivity, a metal’s electronic configuration, particularly of the d band, has been proposed as an index of catalytic Dowden et aZ.64 further proposed that metal oxides share a similar dependence based on their metal ion configuration.The observed reactivity of CuO in this study conforms to this theory since CuO possesses a relatively unstable d9 configuration, while Cu,O, although having a complete d shell, is uniquely unstable as assessed by the d-s promotion energy.64 The change in acidity and basicity of oxides follows two simple rules:65 (1) acidity increases with an increase in charge of the transition-metal ion and (2) proceeding from left to right within a specific period, acidity increases.Assuming the first rule takes precedence over the second, these two rules, taken in conjunction, pinpoint CuO as being one of the most basic oxides examined in this study. Chemisorbed oxygen is known to have strong basic characteristics, 53, 66 and hydrazine, although normally considered a Lewis base, is a source of protons. In addition to the Lewis basicity ascribed to it, adsorbed oxygen may act as an ‘adsorption promoter’ by creating Lewis acidity (electron deficiency) at adjacent metal atoms.66 These perturbed atoms are stronger Lewis-acid sites than metallic copper atoms and may interact with lone pairs of electrons on the hydrazine molecule.In this hydrazine-metal interaction, hydrazine would be considered a Lewis base, in accordance with the proposal of Eberstein and Glassrnan6, of bond formation between the nitrogen atoms in hydrazine and the incomplete d-orbitals of the metals. An increased reactivity can be ascribed not only to these acid-base effects but also to3278 Hydrazine Reduction of Transition-metal Oxides changes in the surface coverage of hydrazine. As increased hydrazine surface coverage (0) on the metal oxide is expected owing to (i) promotion of surface acidity by adsorbed oxygen as discussed above, resulting in enhanced N-metal bonding and (ii) an increase in the heat of adsorption caused by strong hydrogen-oxygen bonding following dissociative ad~orption.~~ Morphology of Reduced Copper( n) Oxide X.P.S.Studies In addition to the role of an oxide's physicochemical properties, the reactivity of a metal oxide toward hydrazine may be enhanced by morphological changes in the solid, particularly if such changes provide increased surface areas for reaction. Although X-ray photoelectron spectra of hydrazine-treated samples indicated elemental copper based on the position of the Cu 2p peaks (fig. 4) and the oxygen : metal ratio, visually the specimens did not return to the characteristic colour of this metal. These observations suggest the formation of a metallic layer upon bulk-like CuO. For this reason the morphology of reduced CuO was studied further using angle-resolved X.P.S.A thickly oxidized (i.e. > 1 pm) CuO layer was reduced in situ with hydrazine at conditions appropriate for partial surface reduction (200000 langmuir at 295 K). With the sample plane perpendicular to the analyser, the X-ray photoelectron spectrum of the Cu 2p region showed a mixture of CuO and Cu,O/Cu (fig. 5). However, at an electron take-off angle of lo", with its corresponding five-fold increase in surface sensitivity, a decrease in the CuO content was evident (fig. 5). The principal peaks shifted to the lower binding energies indicative of either metallic copper or Cu,O, while the shake-up satellites characteristic of CuO decreased in intensity indicating a surface enrichment of a more reduced species.The presence of the bulk-like CuO substrate was further confirmed by argon ion bombardment. A fully reduced sample, as assessed by the Cu 2p and 0 1s spectra, was rigorously sputtered to remove the metallic surface layer. Although this technique has inherent chemical reduction tendencies for CUO,~* an increased oxygen content after sputtering (ca. 10 nm) also indicated the existence of sub-surface oxide. Owing to density changes in the crystal lattice upon transformation from CuO to metallic copper, a roughening or pitting of the surface may be expected, resulting in exposure of underlying CuO for further reaction with hydrazine. The newly exposed CuO in these pores may have minimal contribution to angle-resolved X-ray photoelectron spectra, owing to the absence of a line-of-sight electron trajectory from these regions to the analyser.Microgravime tric Studies Confirmation of the proposed change in morphology suggested above was evident from microgravimetric studies that indicated increased surface areas following CuO reduction in hydrazine. Surface areas of copper wool in the sequential stages of prereduction (H2, 673 K, 8 h), oxidation (86 mg 0, per g Cu, ca. 50 nm CuO), and hydrazine reduction (298 K, 10 h) were typically 1.5,0.6, and 2.5 m2 g-l, respectively. The decrease in surface area upon oxidation may be attributed to annealing and/or obscuring of surface defects by the oxide layer.67 The increase in surface area upon reduction in hydrazine appears to result from porosity and roughening created during removal of ca.97% of the oxygen in the CuO layer. Thus the relatively high reactivity of CuO in comparison with the other first-row transition metal oxides may also be due to the increased surface area produced during the oxide-N,H, reaction, since this roughening helps to expose underlying CuO.D . M. Littrell, D. H . Bowers and B. J. Tatarchuk 3279 97 5 950 binding energy/eV 925 Fig. 4. X-Ray photoelectron spectra of the Cu 2p1/2-3,2 doublet obtained from the indicated copper species. (a) Cu, (b) Cu,O, (c) CuO. 975 92 5 binding energy/eV Fig. 5. Angle-resolved Cu 2p1/2-3,2 spectra of partially reduced CuO. (a) 8 = lo", (6) 0 = 90".3280 Hydrazine Reduction of Transition-metal Oxides Although increased surface areas following hydrogen reduction of CuO have been reported previously,68* 69 comparisons of hydrazine and hydrogen reduction treatments suggest that hydrazine reduction is more spontaneous and provides greater increases in surface area than does hydrogen.Oxidized copper wools (ca. 50nm of CuO) with surface areas of 0.6 m2 g-l were reduced in 100 kPa of hydrogen at 423 K for 4.5 h. Temperatures of 423 K were required during hydrogen reduction to provide reduction rates similar to those observed in 600 Pa of hydrazine at room temperature. Hydrogen reduction was halted after removal of ca. 95% of the added oxygen in order to correspond with typical conversion levels provided by hydrazine reduction. Surface areas of hydrogen reduced specimens (1.8 m2 g-') were near those of the initial prereduced copper specimens (i.e.1.5 m' g-I) and ca. 60% less than those produced by hydrazine reduction at 295 K. These differences in surface area may be partially attributed to relaxation effects resulting from the higher temperatures employed during hydrogen reduction, yet thermal annealing of hydrazine reduced specimens proved that the reduced oxides possess surface areas which are thermally stable at temperatures ~ 5 7 3 K. Indeed, specimens with surface areas of ca. 2.5 m2 g-l when heated in vacuo (0.06 Pa) at 423 or 573 K for 4.5 h exhibited no losses in surface area, while annealing at 673 K for 24 h reduced the surface areas to ca. 1.4 m2 g-l. These data indicate that the surface areas created by hydrazine reduction are marginally stable in vacuum, and that increases in surface area cannot be solely attributed to decrease relaxation effects at the lower reduction temperatures required for hydrazine reduction.TEM Studies In support of X.P.S. data and microgravimetric measurements, transmission electron microscopy (TEM) was used to investigate the nature of surface roughness developed during the CuO-N,H, reaction. Micrographs of hydrogen pre-reduced copper grids (plate 1) provide evidence of smooth surface contours associated with these relatively low- surface-area materials. Subsequent oxidation at 623 K and 100 kPa for 12 h (ca. 50 nm of CuO) provided the CuO filaments shown in plate 2, consistent with previous microscopic observations of oxidized copper. 1 7 9 70 These filaments, found predominantly at the curved portions of the grid, are known to be composed of CuO and generally comprise > 1 % of the total oxygen in the scales,17 depending on the oxidation condition^.^^ Subsequent exposure of the oxidized grids to hydrazine (530 Pa, 298 K, 9 h) had two effects, the first being a folding over of the filaments (plate 3) caused by reduction of the filaments to metallic copper.The second was the production of surface roughness corresponding to an increased surface area, as evident from the fissures shown in plates 3 and 4. Thus, increases in surface area may be derived from the formation of reduced oxide whiskers (i.e. metal fibres) and irregular pitting of the surface. Conclusions The reaction between the transition-metal oxides (V20,, Cr203, Mn,O,, Fe203, Co,O, NiO, CuO and ZnO) and hydrazine was qualitatively and quantitatively assessed by X-ray photoelectron spectroscopy.The oxides ' relative ease of reduction increased monotonically with the heat of formation of the oxide per oxygen molecule (i.e. - AGg8 mole oxygen), suggesting a strong correlation between bulk and surface thermodynamics. CuO merited more extensive study based on its relatively high reactivity with hydrazine. It is suggested that its relative reactivity may be explained from consideration of the thermodynamic and acid-base properties of the CuO-N,H, reaction.J. Chem. SOC., Faraday Trans. 1, Vol. 83 part I 1 Plates 1 and 2 Plate 1. Electron micrograph of a prereduced copper grid (H2, 673 K, 9 h) showing a low-surface area sample. Plate 2. Electron micrograph of an oxidized copper grid (02, 723 K, 9 h) showing whisker growth.D. M. Littrell, D. H. Bowers and B. J. Tatarchuk (Facing p . 3280)J . Chem. SOC., Faraday Trans. I , Vol. 83 part 11 Plates 3 and 4 Plate 3. Electron micrograph of a hydrazine-reduced CuO/Cu grid (530 Pa, 298 K, 9 h) showing formation of metallic whiskers. Plate 4. Electron micrograph of a hydrazine-reduced CuO/Cu grid (530 Pa, 298 K, 9 h) showing pits formed on the contours. D. M. Littrell, D. H. Bowers and B. J. TatarchukD. M. Littrell, D. H. Bowers and B. J. Tatarchuk 328 1 Adsorbed oxygen acts as an ‘adsorption promoter ’ by creating Lewis-acid (electron deficient) sites on adjacent metal atoms for increased interaction with adsorbing hydrazine. An increase in hydrazine surface coverage may result from this action as well as from an increased adsorption energy owing to strong hydrogen-oxygen bonding and water formation during the reaction. Enhanced reactivity may also result in part from morphological changes of the oxide which provide increased surface areas for reaction.Microgravimetry and TEM suggest an increase in surface area associated with reduction of CuO by hydrazine at 298 K that is more extensive than reduction by hydrogen at temperatures up to 423 K. The porosity associated with reduction in hydrazine may allow exposure of the underlying oxide, thereby driving to near completion the reduction of thick (ca. 120 nm) oxide layers at room temperature. This work was partially funded by the U.S. National Aeronautics and Space Administration (NASlO-11027) and partially by the Space Power Institute as funded by the SDIO Innovative Science and Technology Office and the Defense Nuclear Agency under DNA contract no.001-85-C-0183. The assistance of Mr Ray Cocco during TEM studies is also acknowledged. References 1 D. M. Littrell and B. J. Tatarchuk, J. Vac. Sci. Technol., Part A , 1986, 4, 1608. 2 D. M. Littrell and B. J. Tatarchuk, Hydrazine Reduction of’ Transition Metal Oxides: In Situ Characterization using X-ray Photoelectron Spectroscopy, presented to the 32nd National Symposium and Topical Conference of the American Vacuum Society, Houston Texas, November 19-22, 1985 (unpublished). 3 L. F. Audrieth and B. A. Ogg, The Chemistry of Hydrazine (Wiley, New York, 1951) and references cited within.4 A. J. Clark and W. F. Pickering, J. inorg. Nucl. Chem., 1967, 29, 836. 5 M. W. Rophael, Surf. Technol., 1982, 16, 235; Chem. Abs., 97: 134199h. 6 W. J. Ward, P. U. Labine and D. A. Redfield, Ammonia Plant S a j , 1979, 21, 57. 7 M. Grunze, Surf Sci., 1979, 81, 603. 8 M. H. Matloob and M. W. Roberts, J. Chem. Res. (3, 1977, 336. 9 V. G. Rienacker and J. Volter, Z . Anorg. Allg. Chem., 1959, 302, 292. 10 M. H. Matloob and M. W. Roberts, J . Chem. Soc., Faraday Trans. 1 , 1977, 73, 1393. 11 J. L. Falconer and H. Wise J. Card., 1976, 43, 220. 12 J. P. Contour and G. Pannetier, J. Catal., 1972, 24, 434. 13 R. C. Cosser and F. C. Tompkins, Trans. Faraday Soc., 1971, 67, 526. 14 R. C . A. Contaminard and F. C. Tompkins, Trans. Faraday SOC., 1971, 67, 545. 15 D.W. Johnson and M. W. Roberts, J . Electron Spectrosc. Relat. Phenom., 1980 19, 185. 16 H. H. Madden and D. W. Goodman, Surf. Sci., 1985, 150, 39. 17 E. A. Gulbransen, T. P. Copan and K. F. Andrew, J. Electrochem. Soc., 1961, 108, 119. 18 J. Block, 2. Phys. Chem. N.F., 1972, 82, 1. 19 C. J. Groeneboom, G. Sawatzky, H. J. De Liefde Meijer and F. Jellinek, J . Orgunomet. Chem., 1974, 20 R. Larsson, B. Folkesson and G. Schon, Chem. Scr., 1973, 3, 88. 21 V. I. Nefedov, Ya. V. Sayln’, A. A. Chertkov and L. N. Padurets, Russ. J. Inorg. Chem. (Engl. Transl.), 22 V. I. Nefedov., D. Gati, B. F. Dzhurinskii, N. P. Sergushin and Ya. V. Salyn’, Russ. J. inorg. Chem. 23 I. Ikemoto, K. Ishii, S. Kinoshita, H. Kuroda, M. A. Alario Franco and J. M. Thomas, J. Solid State 24 G.C. Allen, M. T. Curtis, A. J. Hopper and P. M. Tucker, J. Chem. Soc., Dalton Trans., 1973, 16, 25 G. C. Allen and P. M. Tucker, inorg. Chim. Acta, 1976, 16, 41. 26 J. C. Carver, G. K. Schweitzer, and T. A. Carlson, J. Chem. Phys., 1972, 57, 973. 27 A. Aoki, Jpn J. Appl. Phys., 1976, 15, 305. 28 M. Oku and K. Hirokawa, J. Electron Spectrosc. Relat. Phenom., 1976, 8, 475. 29 M. Oku, K. Hirokawa and S. Ikeda, J. Electron Spectrosc. Relat. Phenom., 1975, 7, 465. 30 H. F. Franzen, and M. X. Umana, J. Solid State Chem., 1976, 18, 363. 76, C4. 1974, 19, 785; Zh. Neorg. Khim., 1974, 19, 1443. (Engl. Transl.), 1975, 20 1279; Zh. Neorg. Khim., 1975, 20, 2307. Chem., 1976, 17, 425. 1675.3282 Hydrazine Reduction of Transition-metal Oxides 31 N. S. McIntyre, and D. G. Zetaruk, Anal.Chem., 1977, 49, 1521. 32 K. Kishi and S. Ikeda, Bull. Chem. SOC. Jpn, 1973, 46, 341. 33 G. C. Allen, M. T. Curtis, A. J. Hooper, and P. M. Tucker, J. Chem. SOC., Dalton Trans., 1974, 34 T. J. Udovic, Ph.D. Dissertation (University of Wisconsin-Madison, 1982). 35 N. S. McIntyre and M. G. Cook, Anal. Chem., 1975, 47, 2208. 36 K. S. Kim, Phys. Rev. B, 1975, 11, 2177. 37 N. S. McIntyre, T. E. Rummery, M. G. Cook and D. Owen, J. Electrochem. SOC., 1976, 123, 1164. 38 K. S. Kim and N. Winograd, Surf. Sci., 1974, 43, 625. 39 K. S. Kim, W. E. Baitinger, J. N. Amy and N. Winograd, J . Electron Spectrosc. Relat. Phenom., 1974, 40 K. S. Kim and R. E. Davis, J. Electron Spectrosc. Relat. Phenom., 197211973, 1, 251. 41 L. J. Matienzo, L. 1. Yin, S. 0. Grim and W.E. Swartz, Jr, Znorg. Chem., 1973, 12, 2762. 42 G. Schon, Surf. Sci., 1973, 35, 96. 43 S. W. Gaarenstroom and N. Winograd, J . Chem. Phys., 1977, 67, 3500. 44 J. H. Scofield, J. Electron Spectrosc. Relat. Phenom., 1976, 8, 129. 45 D. R. Penn, J. Electron Spectrosc. Relat. Phenom., 1976, 9, 29. 46 D. M. Littrell, M. S. Thesis (Auburn University, 1986). 47 A. Ronnquist and H. Fischmeister, J. Znst. Met., 196041, 89, 65. 48 R. F. Tylecote, Metallurgia, 1956, 53, 191. 49 J. Haber, J. Stoch and L. Ungier, J. Electron Spectrosc. Relat. Phenom., 1976, 9, 459. 50 C . T. Au and M. W. Roberts, Chem. Phys. Lett., 1980, 74, 472. 51 T. Robert, M. Bartel and G. Offergeld, Surf. Sci., 1972, 33, 123. 52 C. T. Au, J. Breza and M. W. Roberts, Chem. Phys. Lett., 1979, 66, 340. 53 K. Kishi and S . Ikeda, Appl. Surf. Sci., 1980, 5, 7. 54 L. Moroney, S. Rassias and M. W. Roberts, Surf. Sci., 1981, 105, L249. 55 C. T. Au, S. Singh-Boparai, and M. W. Roberts, J . Chem. SOC., Faraday Trans. I , 1983, 79, 1779. 56 K. Tanaka and K . Tamaru, J. Catal., 1963, 2, 366. 57 R. Ugo, Proc. 5th Int. Cong. Catal. (North-Holland, Amsterdam, 1973), p. 13-19. 58 P. Sabatier, Ber. Dtsch. Chem. Ges., 1911, 44, 2001. 59 W. J. M. Rootsaert and W. H. M. Sachtler, Z. Phys. Chem., 1960, 26, 16. 60 A. A. Balandin, Adv. Catal., 1958, 10, 120. 6 1 A. A. Balandin, Surface Chemical Compounds and Their Adsorption Phenomena (Moscow University 62 I. J. Eberstein and I. Glassman, Prog. Astronaut. Rocketry, 1960, 2, 351. 63 M. McD. Baker and G. I . Jenkins, Ado. Catal., 1955, 7, 1. 64 D. A. Dowden, N. Mackenzie and B. M. W. Trapnell, A h . Catal., 1957, 9, 65. 65 0. V . Krylov, Catalysis By Nonmetals (Academic Press, New York, 1970). 66 M. A. Barteau, M. Bowker and R. J. Madix, Surf. Sci., 1980, 94, 303. 67 T. N. Rhodin, J. Am. Chem. SOC., 1950, 72, 4343. 68 W. D. Bond, J. Phys. Chem., 1962, 66, 1573. 69 T. Takeuchi, 0. Takayasu and S . Tanada, J . Catal., 1978, 54, 197. 70 G. M. Raynaud and R. A. Rapp, Oxid. Met., 1984, 21, 89. 1525. 5, 351. Press, Moscow, 1957). Paper 61 1544 ; Received 28th July, 1986

ISSN:0300-9599    

DOI:10.1039/F19878303271

出版商:RSC    

年代:1987

数据来源: RSC

摘要:

J . Chern. Soc., Faraday Trans. I , 1987, 83 (ll), 3283-3293 Infrared Study of the Adsorption of Non-ionic Surfactants on Silica Yves Lijour, Jean-Yves Calves and Pierre Saumagne" Lab . Spec t r och irn ie Mole'culaire, Un ive rsite' de Bre tagne Occiden tale, 29287 Brest Ce'dex, France An infrared study of the adsorption of octylphenolethoxylates with an average of 1,lO and 70 oxyethylenic groups at the silica+arbon tetrachloride interface is reported. The adsorption occurred mainly uia hydrogen bonding between the oxygen atoms of the hydrophilic chain and the free silanols. No chemisorption was found to take place. The surfactant molecules presented a flat configuration at low coverage, but at increasing coverage they were adsorbed in a more upright configuration as fewer oxyethylenic groups were able to interact with surface silanols owing to steric crowding.Finally, at saturation, the last molecules were adsorbed vertically through the terminal hydroxy group. The adsorption of polyethylene glycols and non-ionic surfactants has been receiving a lot of attention for many years1 Most of the previous work has been concerned with the determination of adsorption isotherms of polyethylene glycols2v and alkylphenol eth~xylates.~-l' It is now generally accepted that the adsorption of non-ionic surfactants on silica involves hydrogen bonds between the oxygen atoms of their oxyethylenic chains and the silanol 8 v 14* l9 however, the actual configuration of the adsorbed layer and the possible modifications as a function of surface coverage remain speculative.Furthermore, a chemisorption process which has been proposed by Savintseva et aZ.16 and rejected by several other authors4*14 has not been entirely ruled out. Although infrared spectroscopy is well suited to characterize adsorbate interactions, this technique has evoked little interest for the study of the adsorption of non-ionic ~ u r f a c t a n t s , ~ ~ ? ~ ~ probably because of technical and experimental complications. In the past decade, Rochester has developed a method allowing an 'in situ' study of the solid-liquid interface,20-22 unlike previous experiments which implied a phase separation before analysis. l6 We took advantage of these recent developments to bring a complementary approach to the study of the adsorption of some octylphenolethoxylates. The type of interaction and the adsorption mechanism will be discussed. Experiment a1 The experimental device allowing an 'in situ' study of the solid-liquid interface was similar to that described by Rochester2' (fig.1) and included a fluorite window cell, a vertical high- temperature section and a circulating liquid system. All joints were made of Viton O-rings and Teflon. However, an important modification consisted in the insertion of a platinum wire (0.05 mm diameter) into the disc during pressing so that no sample holders were needed and the minimum pathlength between the two windows could be significantly reduced from 3 mm to the oxide disc thickness (ca. 0.2 mm). However, 0.5 mm was found to be the optimum pathlength in order to alleviate problems of diffusion.A pellet of Aerosil 200 (Degussa, average specific area 200 m2 g-') was made by pressing (at 70 MN m-2) ca. 20 mg of powder along with the platinum wire in a 13 mm 32833284 Adsorption of Non-ionic Surfactants on Silica w platinum wire counterweight platinum wire inserted in the oxide disc gas and liquids joint drain tap Fig. 1. Infrared cell with the pump and the high-temperature section for an ‘in situ’ study of the solid-liquid interface. diameter die. The sample was attached to the glass-coated iron counterweight of the winding device and was mounted vertically above the cell. The disc could be set in the upper section for high-temperature treatment or lowered into the cell by action of an outside magnet on the counterweight.The infrared windows were vertically displaced so as to facilitate the lowering of the disc into the beam area (fig. 1). Standard vacuum techniques were used to degas the sample and to introduce the solutions. A spectrum of the pellet was then recorded using a Philips Pye-Unicam SP-2000 dispersive infrared spectrophotometer. A solution was prepared from the dry compound diluted in carbon tetrachloride (spectroscopic grade) stored over molecular sieves and injected into the cell under a dry nitrogen atmosphere. Carbon tetrachloride was used because of its infrared transparency throughout most of the region of interest. Adjustment of the infrared beam on the sample was achieved by maximizing the intensity of the free hydroxyl peak (3690 cm-’ for silica in CCl,).No compensation of the solution in the reference beam was performed and the solute absorption was manually subtracted so as to only get the spectrum of the adsorbed species and of the Aerosil. The pump was started and the adsorption was monitored ‘in situ’. All experiments were carried out at room temperature. The non-ionic surfactants to be adsorbed were octylphenolethoxylates with the general formula C,H,, 0 (OCH,CH,), -OH supplied by Rohm and Haas (type Triton X). Also used was Triton CF-54 with aY. Lijour, J-Y. Calves and P. Saumagne Table 1. Average number of ethylene oxide groups per surfactant calculated from the HLB data HLB X Triton X-15 3.6 1.03 Triton X-100 13.5 9.7 Triton X-705 18.7 67.30 Triton CF-54 13.5 9.72 3285 terminal t-butoxy {OC(CH,),} group instead of a single OH group.All Tritons were polydisperse and the values of x given in table 1 represent the average number of ethoxylate groups calculated from their hydrophilic-lipophilic balance (HLB). All pure Tritons have infrared bands at similar positions. Aliphatic CH groups are represented by strong overlapping bands with maxima at 2960 and 2880cm-'. The relative intensity of the 2880 cm-' band increased as a function of x so that this band is likely to represent vibrations of the ethoxylate groups, and the maximum at 2960 cm-' can be attributed to the hydrophobic alkyl part of the molecules. A shoulder at 3060 cm-l is consistent with the presence of aromatic CH. Two broad bands at 1360 and 1470 cm-l are assigned to S(CH) deformation modes and finally, a doublet at I5 15 and 1615 cm-' corresponds to v(C = C ) vibrations of the phenyl group.The surfactants used in this study were assumed to be essentially present as monomers in carbon tetrachloride since several studies have reported a weak tendency for similar non-ionic surfactants to aggregate in non-polar solvents such as cc14.23 Results and Discussion Nature of the Interactions The surface structure of silica is now well established as a result of many infrared spectroscopic studies that have demonstrated the presence of free and associated hydroxyl groups, having a sharp peak at 3748 cm-' and a broad feature centred near 3450 cm-', respectively. A thermal treatment at 120 "C under vacuum completely removes the water from the surface. As a consequence, the free OH peak at 3748 cm-l increases in intensity and the broad associated OH band is significantly reduced and shifts to 3550cm-'. As the treatment temperature is raised to 400 "C and then to 600 "C, the adjacent surface hydroxyls progressively condense with subsequent dehy- droxylation and formation of siloxane bridges.After a 600 "C treatment, the surface no longer presents associated hydroxyls. Their number represents ca. 70 YO and 20 YO of the total number of surface hydroxyls after a treatment at 120 and 400 "C, re~pectively.~~ Immersion of silica in carbon tetrachloride leads to a downward shift of the free OH to 3690 cm-' with a broadening to low wavenumbers. This has been attributed to weak interactions between the silanols and the The broad band at 3550 cm-' is only slightly affected because of stronger interactions between silanol groups than with carbon tetrachloride.Adsorption of Triton X-15, X-100, X-705 and CF-54 on Aerosil degassed at 600 "C Fig. 2 and 3 show the evolution as a function of time of the infrared spectra in the region 2600-000 cm-' recorded during the adsorption of Tritons X-15, X-705 (fig. 2) and Tritons X-100, CF-54 (fig. 3). The surfactant adsorption was demonstrated by a3286 Adsorption of Non-ionic Surfactants on Silica , I , ' , ' , , , , I , , l & , , , l , , , 00 3500 3000 2 10 wavenumber/cm-' Fig. 2. Infrared spectra of Aerosil (degassed at 600 "C) in solution: A, 2 x lop3 rnol dmp3 Triton X-15, (a)-(/z): initially, 5 min, 30 min, 1 h, 2 h, 4 h, 10 h, 24 h; B, 2 x mol dm-3 Triton X-705, (a)-@): initially, 5 min, 30 min, 1 h, 1 h 30 min, 2 h, 2 h 30 min, 3 h.I A I 1 I' 1 ' 1 ' c- - - I , I, I , , , 10 0 3500 3000 2600 4000 3500 3000 1 wavenumber/cm-' 00 Fig. 3. Infrared spectra of Aerosil (degassed at 600 "C) in solution: A, 2 x lod3 mol dm-3 Triton X-100, (a)-(i): initially, 5 min, 30 min, 1 h, 1 h 30 min, 2 h, 3 h, 4 h, 5 h ; B, 2 x mol dmh3 Triton CF-54, (a)-(g): initially, 5 min, 30 min, 1 h, 1 h 30 min, 2 h, 3 h.Y. Lijour, J-Y. Calves and P. Saumagne 3287 progressive growth of bands in the 2800-3000 cm-' region and below 2000 cm-l by the formation of weak bands (not shown) at 1360, 1470, 1515 and 1615 cm-' located at the same positions as for the pure Tritons (see above). The free OH peak at 3690 cm-' steadily decreased in intensity and eventually disappeared in the case of Tritons X-100, CF-54 and X-705.However, only ca. 50 % of the free surface hydroxyl groups interacted with Triton X-15. For each of these surfactants a broad band due to associated hydroxyls grew in the 3 100-3500 cm-l region, indicating a strong interaction between surface silanols and adsorbed species [340 d Av(OH)/cm-l d 3901. These associated OH bands were located at the same position throughout the adsorption of each surfactant, indicating a constant energy of interaction at increasing coverage. The presence of isosbestic points at 3630 cm-l (denoted 'i') in fig. 2 and 3 demonstrated the correspondence between the disappearance of the free OH and the growth of the associated OH even upon adsorption of Triton CF-54, which has no terminal hydroxyl.This clearly shows that the surfactant adsorption mainly occurred through hydrogen bonding between the free silanols and the adsorbed species. Chemisorption can be excluded because the decrease of the 3690 cm-l peak would not give rise to a corresponding increase in the associated OH band. This also precludes the participation of the terminal hydrogen of the surfactant in an adsorption mechanism which would have involved an electrophilic attack on the free silanols or on the siloxane bridges (the latter are known to be poor electron donorsz6) or on other adsorbed surfactant molecules with formation of multilayers. The presence of a single layer is in agreement with a result showing that Triton X- 100 was adsorbed in a monolayer at the silicaxyclohexane interface.8 However, other configurations are possible at the more complex silica-water inter- face.4' l4 The relative intensity of the 2880 cm-l band was less in the adsorbed state than in solution, giving evidence for the perturbation of the ether groups upon adsorption.The functional groups of the surfactants that are engaged in hydrogen bonding with the surface free hydroxyls are therefore the ethoxylate chains. Nonetheless, a band at 3600 cm-' formed upon adsorption of Triton X- 15 (fig. 2) indicated that another weaker hydrogen bond [Av(OH) = 90 cm-l] existed in this case. A band at a similar position has been observed when benzene was adsorbed on silica and has been attributed to a weak interaction between the silanol groups and the n-electrons of the aromatic nu~leus.~' A similar type of hydrogen bonding is therefore likely to occur when Triton X-15 is adsorbed on the free surface hydroxyls. This could be explained because in Triton X-15, the single ether group leads to a lack of flexibility in the molecule.Since the affinity between this group and the free silanols is strong [Av(OH) = 340 cm-'I, Triton X-15 therefore adsorbs via its hydrophilic part, but this brings its phenyl and lipophilic alkyl groups close to the surface. The first consequence is the formation of a silanol-aromatic nucleus interaction represented by the band at 3600 cm-l in the infrared spectrum. Secondly, the presence of a hydrophobic group nearby the surface restrains the access to some adsorption centres according to scheme I .This blocking effect would explain why Triton X- 15, unlike Tritons X- 100, CF-54 and X-705 which are more flexible, does not saturate the surface. Additional evidence for this will be given below by estimating the number of points of attachment (hereafter called 'segments') which interact with the silanols as a function of the surface coverage. Adsorption of Triton X-15, X-100 and X-705 on Aerosil degassed at 120 and 400 "C Similar experiments were conducted with a silica outgassed at 120 and 400 "C. As an example, fig. 4 shows the infrared spectra recorded during the adsorption of Triton X- 100 on a sample degassed at 120 and 400 "C. As described above, the surfactant3288 Adsorption oJ Non-ionic Surfactants on Silica H \ b /?, 0 H '0-CH2-CH,;O 0 , I I I 1 i CH H C-C--H I I I 31 a3H 0 P I /& /" f \o /$ ,o,s ; \o 7; \ /: t \o,s /s ;\o / 0 0 0 0 0 0 O 0 0 0 0 Scheme 1.I " " I " ' 1 ' I ' ' ' I ' ' ' A B I I 1 1 , , 1 1 1 , , 1 , , , 3000 2600 4000 3500 3000 2600 4000 3500 wavenumber/cm-' Fig. 4. Infrared spectra of Aerosil: A, degassed at 120 "C in a solution of 2 x mol dm-3 Triton X-100, (u)-(g): initially, 5 min, 30 min, 1 h, 1 h 30 min, 2 h; B, degassed at 400 "C in a solution of 2 x mol dm-3 Triton X-100, (u)-(i): initially, 5 min, 30 min, 1 h, 1 h 30 min, 2 h, 3 h, 4 h, 15 h. adsorption led to a decrease and ultimate disappearance of the free OH peak at 3690 cm-l, regardless of the relative number of free silanols. The differences consisted in the positions and bandwidths of the growing associated OH bands, possibly indicating the superposition of the initial band at 3550 cm-' on a band centred at 3310 cm-l resulting from interactions between Triton X- 100 and surface hydroxyl groups.However, adsorption on the adjacent hydroxyls could not be determined because the fate of the 3550 cm-l band was unclear. The participation of adjacent silanols in the adsorption can only be assumed because of their proximity with the free hydroxyl groups perturbed by the oxyethylenic chain. This possibility has already been raised by Rochester and Gellan.4 Similar conclusions could be drawn for both Triton X-15 and X-705.Y. Lijour, J-Y. Calves and P. Saumagne Table 2. Extinction coefficients and K , values for Tritons E,/m2 mol-' K,,/ 1 O6 mol Triton X-15 33.8 + 8.0 (2960 cm-') 3.9+ 1.0 Triton X-100 53.8 5 13.5 (2960 cm-') 2.5 k0.6 Triton X-705 497+ 124 (2880 cm-') 0.3 k0.07 3289 Table 3.Amount of adsorbed surfactant and average number of adsorbed segments as a function of pretreatment temperature amount of adsorbed surfactant 400 "C 600 "C S mg g-' mol g-l mg g-' mol 8-l 400 "C 600 "C Triton X-15 36 1 . 4 3 ~ 34 1 . 3 5 ~ lop4 2.4 2 Triton X-100 83 1.31 x 82 1 . 3 0 ~ lop4 5 5 Triton X-705 70 2.20x 10-5 60 1 . 9 0 ~ 10-5 35 32 Since free surface hydroxyl groups have been shown to be strong adsorption sites for these non-ionic surfactants, attempts have been made to estimate the number of segments in interaction with these centres as a function of the surface coverage. Adsorption Mechanism In order to estimate the number of ethoxylate segments per surfactant molecule attached to the free silanols, we calculated the number of adsorbed species as a function of the free surface hydroxyls perturbed by the adsorption. Quantitative Measurements Borello et a1.28 established a proportionality between the optical density of the 3750cm-l band and the number of free hydroxyl groups for an Aerosil sample and calculated its extinction coefficient ( E , , , ~ = 3.5 & 0.1 m2 mol-I).Other studies reported a value of 8.4 m2 m ~ l - ' . ~ ~ In a similar way, we estimated the extinction coefficient of the free OH peak at 3690 cm-' by measuring its intensity for a variety of samples of known masses degassed at different temperatures. Data on the surface hydroxyl population were those published by Fink and Muller.24 A simple application of the Beer-Lambert law gave E,,,, = 1 1 .O & 2.0 m2 mol-', corresponding to an optical density of 1 for 12 f 2 pmol of free silanols.A spectroscopic determination of the amount of adsorbed surfactant was made ' in situ' by assuming a direct relationship with the intensity of its v(CH) bands in the 2800-3000 cm-' region. We assumed that the extinction coefficient did not vary throughout the adsorption and was identical to that measured for the compound in solution. This is probably true for the 2960 cm-l band, which was similar for both the surfactant in solution and in the adsorbed state. However, the 2880cm-' band, corresponding to vibrations in the polyethoxylate chain, although affected by the adsorption, had to be used in the case of Triton X-705 since the 2960 cm-l band was only present as a shoulder relative to the intense 2880 cm-' band.Classical standardization methods gave the extinction coefficients listed in table 2. From these values, the number3290 Adsorption of Non-ionic Surfactants on Silica I 0.41 / I I* 0 400 800 0 200 400 tlmin Fig. 5. Evolution as a function of time of the free OH peak at 3690 cm-l (0) and of the v(CH) bands at 2960 cm-l (or 2880 cm-') ( +) during adsorption of (a) Triton X-15, (b) Triton X-100 and (c) Triton X-705 on Aerosil degassed at 400 "C.Y. Lijour, J-Y. Calves and P. Saumagne 329 1 K, of moles corresponding to an optical density of 1 at the frequency v was deduced (table 2). Adsorption Mechanism From these considerations, the surfactant uptake and the average number of segments s in interaction with the free silanols could be calculated when no changes occurred in the infrared spectra.Table 3 lists those values for the adsorption on Aerosil treated at 400 and 600 "C. It is observed that the quantity adsorbed perg of substrate is comparable for the two pretreatment temperatures because the number of free silanols per surface unit varies slightly between a treatment at 400 and at 600 "C (1.79 OH per nm2 us. 1.60 OH per nm2). These values are in agreement with those reported by Rupprecht and Liebl, who showed a decrease in the number of adsorbed moles of nonylphenolethoxylates as the length of the oxyethylenic chain increased. l3 It is also noted that the adsorption involved every potential segment of Triton X-15 and only about half of them for Triton X-100 and X-705.Killmann et aL2 calculated from adsorption isotherms that several polyethylene glycols were adsorbed on Aerosil with 0.50 and 0.25 of their segments at low and high coverage, respectively. Rochester and Gellan4 suggested that the final configuration of a non-ionic surfactant with 5 oxyethylenic groups was a looped configuration with no more than half of the oxygen atoms in each chain being linked to the silanols. This is in agreement with the present study from the point of view of the average number of segments adsorbed at saturation. However, this average gives little information and a partial understanding of the adsorption mechanism can only be obtained from a knowledge of the actual number of segments attached as a function of time or surface coverage.Fig. 5 shows the evolution of the intensities of the peak at 3690 cm-l and of the bands at 2960 cm-l (or 2880 cm-l for Triton X-705) us. the reaction time upon adsorption of Triton X- 15, X- 100 and X-705 on Aerosil degassed at 400 "C. Experimental points were fitted by exponential curves with correlation coefficients better than 0.99. The number of segments interacting with the free silanols is a function of time and can be written as s ( t ) = -d(free OH)/d(adsorbed surfactant), i.e. the ratio between the variation in the number of free silanols and the variation in the number of moles being adsorbed. This eauation is eauivalent to d(free silanols)/dt d( adsorbed surfactan t)/ dt ' s(t) = - Because of the correspondence between the intensities of the bands at 3690 and 2960 cm-' (or 2880cm-l for Triton X-705) and quantity of free silanols and adsorbed species, s(t), is the ratio between two differential exponential functions and can be expressed under the general form s(t) = s(0) exp (-kt),l where s(0) represents the number of interacting segments at the beginning of the adsorption and k is a constant.(No assumption about whether the adsorption is a first-order process will be considered. The above equation is only a convenient way to represent the experimental data.) Both values are listed in table 4. The s(0) values are close to the maximum number of available segments, implying that the Tritons are preferentially adsorbed in a 'down' configuration on the hydrophilic surface, as proposed by Rochester and gel la^^,^ and Furlong and Aston.14 Furthermore, these data infer a very flat and extended configuration at low coverage, which is understandable given the strong affinity between the ethoxylate groups and the free silanols.All potential segments may theoretically be involved in interactions bequse the maximum distance between two oxygen atoms in an ethoxy!ate chain is ca. 3.6 A," and after a 400 "C treatment, the surface hydroxyls are 3 to 4 A from each other. As the adsorption proceeds according to eqn (l), the number of interacting segments 109 FAR I3292 Adsorption of Non-ionic Surfactants on Silica Table 4. k values and initial numbers of adsorbed segments klmin-l s(0) Triton X- 15 - 1 0 - 4 2.2 Triton X-100 6 .6 ~ lop3 10 Triton X-705 2.8 x 66 for incoming molecules decreases and tends to zero for Triton X-100 and X-705, whilst the value of k for Triton X-15 infers an almost constant number close to 2 throughout the adsorption process. These results are explainable in terms of molecular flexibility and surface coverage. Thus, at increasing surface coverage, the adsorption sites left vacant are less favourably distributed and the forthcoming surfactant molecules must be adsorbed at a smaller number of segments. This could be achieved by their hydrophobic parts standing-up4 in order to minimize the repulsive forces between the hydrophilic and hydrophobic groups, which would give support to the absence of a silanol-aromatic nucleus interaction for Tritons X-100 and X-705.Conversely, Triton X-15 is not flexible enough to do so and the number of adsorbed segments remains constant throughout the adsorption. As stated earlier, this would prevent a full surface coverage. It must be pointed out that, unlike Rochester’s findings, there is no evidence that at saturation the surfactant molecules, once adsorbed, undergo some structural reorganisation. If this were the case, Triton X-15 would raise its hydrophobic tail, thereby eliminating the blocking effect which prevented a complete coverage. Conclusion Strong hydrogen- bonding interactions between free silanols and ethoxylate segments were found to occur upon adsorption of Tritons X-15, X-100, X-705 and CF-54 at the silica-carbon tetrachloride interface.No chemisorption occurred. These non-ionic surfactants were adsorbed horizontally at low coverage with attachment to silanol groups via all of the ether linkages and the terminal OH group. For molecules subsequently adsorbed, and insofar as their flexibility made it feasible, there were progressively fewer attachments via the ether linkage and, at saturation, the last molecules adsorbed perpendicularly to the surface, only being attached via the terminal OH group. The Delegation GCnerale de la Recherche Scientifique et Technique (D.G.R.S.T.) gave its financial support for this study (grant 82.D0477). Y.L. thanks Dr B. A. Morrow for helpful discussions. References 1 J. S. Clunie and B. T. Ingram, in Adsorption at the Solid-Liquid Interface, ed.G. D. Parfitt and C. H. 2 E. Killmann, J. Eisenlauer and M. Korn, J . Polym. Sci., 1977, 61, 413. 3 E. Kokufuta, S. Fujii, Y. Hirat and I. Nakamura, Polymer, 1982, 23, 452. 4 C. H. Rochester and A. Gellan, J. Chem. SOC., Faraday Trans. I , 1985, 81, 2235. 5 C. H. Rochester and A. Gellan, J. Chem. Soc., Faraday Trans. 1, 1985, 81, 3109. 6 N. L. Kucherova, Yu. L. Verderevskii, A. A. Abramzon and N. A. Klimenko, Ukr. Khim. Zh., 1985, 7 E. Keh, S. Zaini and S. Partyka, Calorim. Anal. Therm., 1985, 16, 43. 8 Li Wailing, G. Yueying, Li Xiao and G. Tiren, Huaxue Xuebao, 1985, 43, 1026. 9 S. A. Savintseva, I. M. Sekisova, V. A. Kolosanova and A. F. Koretskii, Kolloidn. Zh., 1985, 47, Rochester (Academic Press, London, 1983), pp. 105-52. 51, 1254. 901.Y. Lijour, J-Y.Calves and P. Saumagne 10 S. Partyka, S. Zaini and B. Brun, Calorim. Anal. Therm., 1983, 14, 133. 1 1 S. Partyka, S. Zaini, M. Lindheimer and B. Brun, Colloids Surf., 1984, 12, 255. 12 E. Tronel-Peyroz, D. Schumann, H. Raous and C. Bertrand, J . Colloid Interface Sci., 1984, 97, 541. 13 V. H. Rupprecht and H. Liebl, Kolloid Z., 1970, 239, 685. 14 D. N. Furlong and J. R. Aston, Colloids Surf., 1982, 4, 121. I5 J. Rouquerol, S. Partyka, F. Rouquerol, Adsorption at the Gas-Liquid-Soljd Interface (Elsevier, 16 S. A. Savintseva, Z. A. Grankina, I. M. Romashchenko and A. F. Koretskii, Kolloidn. Zh., 1980, 42, 17 N. A. Klimenko, A. A. Tryasorukova and A. A. Permilovskaya, Kolloidn. Zh., 1974, 36, 678. 18 N. A. Klimenko, V. I. Kofanov and E. G. Siralov, Kolloidn. Zh., 1981, 43, 349. 19 J. F. Scamehorn, R. S. Schechter and W. H. Wade, Colloid Interface Sci., 1982, 85, 494. 20 C. H. Rochester, J . Chem. Soc., Faraday Trans. I , 1975, 71, 2478. 21 C. H. Rochester, Progr. Colloid Po1,ym. Sci., 1980, 67, 7. 22 C. H. Rochester, J . Oil Colour Chem Assoc., 1985, 67, 285. 23 P. S. Sheih and J. H. Fendler, J . Chem SOC., Faraday Trans. I , 1977, 73, 1480. 24 P. Fink and B. Muller, Math. Naturwiss. R., 1981, 30, 593. 25 W. D. Bascom, J. Phys. Chem., 1972, 76, 3188. 26 A. V. Kiselev and V. I. Lygin, Infrared Spectra of Surface Compounds (Halstead Press, New York, 27 A. Zecchina, C. Versino, A. Appiano and G . Occhiena, J. Phys. Chem., 1968, 72, 1471. 28 E. Borello, A. Zecchina and C. Morterra, J. Phys. Chem., 1967, 71, 2938. 29 C. H. Rochester, A. R. Acosta Saracual, S. K. Pulton and G. Vicary, J . Chem. SOC., Faraday Trans. I , 30 M. J. Schick, Non-ionic Surfactants (Marcel Dekker, New York. 1967). 3293 Amsterdam, 1982). 592. 1975). 1982, 78, 2285. Paper 612098; Receiued 29th October, 1986

ISSN:0300-9599    

DOI:10.1039/F19878303283

出版商:RSC    

年代:1987

数据来源: RSC