摘要:

AbstractThe selfdiffusion coefficientsDi, of the spherical molecule tetramethylsilane, TMS, and of n‐alkanes have been studied in three binary systems of n‐alkane/TMS in the temperature‐ und pressure range 253.15 ⩽T/K ⩽ 368.15; 0.1 ⩽P/MPa ⩽ 200. The mol fractions of TMS in the mixtures were chosen asxTMS= 0, 0.1, 0.9, and 1; the n‐alkanes were n‐hexane, n‐nonane, and n‐dodecane. Measurements of the mass densities at the chosenxTMS‐values were done in theP,T‐range given above. – The results of theDimeasurements can be rationalized by a polynomialDi=f(P,T). The molar volumes found from the mass density measurements are described byVM=f(p,T) for the range covered by the experiments; they are described by a polynomial, too. Activation energies for the selfdiffusion process have been determined. –Diat constantP,Tdecreases in the sequence n‐hexane, TMS, n‐nonane, n‐dodecane. For the pure substances as well as for the components in the mixtures (Di)max/(Di)min= 3.5 to 4. – The interpretation of the results relays on the “Free Volume” model [1]. From the dataDi=f(P,T) the selfdiffusion coefficients at constant volume have been extrapolated and their dependence fromT1/2is discussed. The results of the measurements are interpreted by assuming folded conformations of the n‐alkanes in the mixtures with TMS. In the mixtures one component can be regarded as the solvent, do

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970102

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractBy means of stopped‐flow experiments equilibrium and rate constants are determined for the weak complexation of the aluminium(III)‐ion with formate, acetate, chloroacetate and benzoate. For the innersphere complex formation both equilibrium and rate constants depend on the nature of the ligand, and a linear free energy relation is observed between rate constants and dissociation constants of the corresponding ac

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970103

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractThe kinetic salt effects in sodium nitrate solutions, up to 5 mol dm−3, on the reaction between hexacyanoferrate(II) and pentaammineaquocobalt(III) have been studied. The experimental trends of the association constant of the reactants,KIP, and the electron transfer rate constant,ket, can be explained within the framework of dielectric continuum models. – To further support this explanation, theKIPandketvalues of the reaction between octacyanomolibdate(IV) and pentaammineaquocobalt(III) in a 0.5 mol dm−3solution of sodium perchlorate have been determined. – The methodology employed in the present work could be used as a general method for analyzing medium and salt effects on electron transfer processes, when one of the reactants shows irreversible behaviour, from the electrochemical point

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970104

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractThe CL study of the oxidation of toluene initiated by AIBN has shown that both triplet and singlet benzaldehyde is formed (T/S≈︁ 10.5). The lifetimes in toluene are: τ5≈︁ 4 · 10−9s and τT≈︁ 1.9 · 10−7s. – In the presence of DPA the kinetic curve of the CL light shows a maximum at [DPA]>10−4M. The CL spectrum of the oxidation of toluene lacks both the fluorescence and phosphorescence peaks of the excited benzaldehyde (due to the very low efficiency of photon emission and very strong quenching by O2and toluene). – Analysis of product distribution by HPLC revealed the formation of benzaldehyde, benzylalcohol, benzylhydroperoxide and benzoic acid. A small amount of H2O2was also detected by spectrophotometry. Since the ratio of aldehyde/alcohol is always higher than unity detailed study of all circumstances led us to the conclusion that benzylperoxy radicals terminate both by the Russell‐mechanism and by the transition state containing two five‐membered rings suggested by Bennett and Summers. – The activation energy of hydrogen abstraction from toluene by benzylperoxy radicals is 53 kJ/mol and the rate constant of this reaction does not differ essentially from the same reaction of ethylbenzene. The kinetic chain length of oxidation calculated from the analytical d

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970105

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractThe dissociation rate constants of 2‐methyl‐2‐nitrosopropane dimer are studied in argon, xenon, carbon dioxide (CO2) chlorotrifluoromethane (CClF3), and trifluoromethane (CHF3) from the gaseous to liquid state at 25.0 and 35.0°. In all solvent fluids, the dissociation rate constant is a decreasing function of solvent density. In argon, xenon, and CClF3, the rate constant at 35° gradually decreases by about 50% with increasing solvent density from ρr≈︁ 0.0 up to 2.5, where ρris a reduced density by the critical density of the solvent. In CO2and CHF3, however, the rate constant shows a large and nonmonotonic dependence on solvent density; the solvent density dependence is large in the low‐ (ρr2.0) density regions, and is small in the medium‐density region (0.5<ρr<1.7). The density dependence of the rate constant in argon and xenon is well reproduced by the Lennard‐Jones fluid model on the basis of the transition state theory. The change in the charge distribution of the reactant molecule is a key to explain the large and nonmonotonical density dependence of the rate

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970106

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractResults of dynamic light scattering experiments with aqueous solutions of benzene[9]3‐arborol (molar mass,M= 1.486 · 103g mol−1; spherical dimension (radius) estimated on the basis of molecular models,a≈︁ 1 nm) at 25° are reported. They indicate that benzene[9]3‐arborol molecules in aqueous solution form aggregates which have dynamic properties similar to that of single polymer chains in good solvents in the cross over region (qrh) ≈︁ 1 (q, absolute value of the scattering vector, (rh, hydrodynamic radius of the scattering particles). A double logarithmic plot of maximum value of the distribution of relaxation rates of the autocorrelation function of the scattered light intensityΓmaxversus theq(0.68 ≤ (q/q+) ≤ 2.40;q+= 105cm−1) gives a straight line with a slopeD*= (2.46 ± 0.05) independent of concentration (Γmax∼ (q/q+)D*). The size of the scattering particles appear not to change with concentration in the concentration range studied (3.5 · 10−3c+≤c≤ 13.37 · 10−3c+;c+= 1 mol dm−3). Values ofD*(2 ≤D*≤ 3) indicate that the experiments are carried out in the non‐universal crossover regime (q rh) ≈︁ 1. From the ratio (Γmax/q2) refering to the limitq0 a hydrodynamic radius ofrhof the orderrh= O(100 nm) is calculated. This is in agreement with the conclusion drawn from theq‐dependence ofΓmax(i.e. (q rh) ≈︁ 1). – The partial molar volume of benzene[9]3‐arborol in aqueous solution increases with concentration only in very dilute solutions. It is practically constant in the concentration range in which the dynamic light scattering experiments are carried out. The surface tension of these solutions at the air/solution interface decreases only slightly with concentration reflectin

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970107

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractAqueous micellar solutions containing cetyltrimethylammonium bromide (CTAB) and solubilized 3‐stilbene carboxylic acid (3‐SC) or 4‐stilbene carboxylic acid (4‐SC) known to exhibit photorheological effects were investigated via (i) oscillatory shear viscometry, (ii) static and dynamic light scattering and (iii) electrically induced birefringence. The presence of 3‐SC and 4‐SC induces the formation of swollen micelles as revealed from light scattering data. The viscosity increase observed upon in situ photoisomerization of 3‐SC and 4‐SC is accompanied by a further increase in micelle size as shown by light scattering data. Only solutions containing 3‐SC at concentration ratioscCTAB/c3‐sc≤ 6.5 show non‐Newtonian flow such as shear thinning, thixotropy and viscoelasticity, which are indicative of the presence of anisometric micelles. Photoisomerization induces non‐Newtonian features in systems containing 4‐SC and increases these features in 3‐SC solutions. Two shear stress relaxation mechanisms are res

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970108

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractMC simulations for a liquid supported monolayer of amphiphilic molecules were carried out within a cubic lattice model using two‐dimensional periodic boundary conditions. The molecules consist of a hydrophilic head and hydrophobic segments. Only excluded volume interactions were taken into account. We varied both the head density and the number of segments. The comparison with attractive interaction including calculations for 15 unit molecules on a cubic lattice provided the same qualitative results in dependence on the head density. The order parameter values in dependence on the head density are greater than the corresponding ones from athermal simulations on a diamond lattice. The difference may arise from the different lattice types. The influence of the chain length on molecular properties as the mean end‐end distance, the mean end‐end projection, the mean height, and the effective layer thickness as well as the order behavior is intensively disc

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970109

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractIt is demonstrated that the fractional Hall plateaux, experimentally observed in some nearly ideal samples at very low temperatures, are manifestations of strongly correlated objects explicitly connected with Coleman's extreme case and Yang's concept of off‐diagonal long‐range order (ODLRO). This interpretation yields (n– 1)/(2n– 1),n= 2,3,… the most stable fractions. The appearance of large even fractions is considered together with a possible explanation of the recently observed fractional Hall states with even numerators in bilayer two‐dimensional electron systems. The present quantum correlations theory also suggests a theoretical analysis of the observed variations in wire‐wound refere

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970110

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractWe built a true alternating current (a.c.) battery that periodically reverses value and sign of its electromotive force (e.m.f.). This a.c. battery is an electrochemical concentration cell that consists of two coupled half cells in which identical oscillating Belousov‐Zhabotinskii (BZ) reactions take place isothermally at 28.0°. The homogeneous BZ oscillations are phase shifted in order to create a potential difference between both half cells. With an increasing load the phase shift between the two half cells decreases (i.e. both oscillations tend to synchronize), consequently the amplitude of the alternating current decreases while the amplitudes of the individual BZ‐oscillators remain unaffected. The e.m.f.‐current diagram of the a.c. battery is analogous to that of direct current batteries. Although the present frequency (period of ∼58 s), current (∼±2.5 μA), e.m.f. (∼±50 mV) and maximum power produced (∼10−7W) are low it should be possible to construct a.c. batteries with improved performances by the use of other c

ISSN:0005-9021    

DOI:10.1002/bbpc.19930970111

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY