摘要:

AbstractWe have measured the1H nuclear magnetic relaxation rates and the self‐diffusion coefficients of (CH3)4N+ions in aqueous solution of (CH3)4NBr as a function of salt concentration and in aqueous mixed electrolyte solution ofx4m (CH3)4NBr + (1 ‐x) 4mMBr, (M = Li, K, Cs) as a function of the mole fractionxof (CH3)4N+. By measuring also the2H relaxation rate of the solvent D2O, we could separate the (CH3)4N+proton relaxation rates into the intra‐ and intermolecular contribution. This allowed the determination of the so‐called association parameterA, which is connected with the integral over the pair correlation function. The results for the cation‐cationA‐parameter show that in the pure (CH3)4NBr solution no or only weak (CH3)4N+‐(CH3)4N+attraction is present, whereas in the mixed electrolyte solutions containing KBr or CsBr a strong association of the hydrophobic cations occurs. With M = Li, this attractive interaction is also present, however less pronounced. The sequence of the effectiveness of the alkali ions is the same as in the so‐called Hofmeister series for salting‐out effects on biologic

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950201

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe Taylor dispersion technique is modified to measure the concentration‐dependent mutual diffusion coefficientDof cetylpyridinium chloride (CPC) + water at 25°C near the critical micelle concentration. The solution flowing into the dispersion tube is changed from a solution of CPC concentrationC−to a solution of concentrationC−+ ΔC, forming an initially‐sharp moving boundary at the tube inlet. The broadened concentration profile across the eluted boundary is followed by using a flow‐through differential refractometer at the tube outlet. A numerical procedure similar to the Boltzmann‐Matano procedure for the analysis of free diffusion profiles yields the values ofDat the concentrations betweenC−andC−+ ΔC, from a single dispersion run.Dfor aqueous CPC is found to drop very sharply as the concentration is raised through the critical mic

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950202

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe Taylor dispersion (peak‐broadening) technique is used to measure the quaternary interdiffusion coefficients of the four‐component systems sucrose + LiCl + KCl + water and tetra‐n‐butylammonium bromide + LiBr + KBr + water at 25°C. The dispersion of the eluted solutes is followed by differential refractometry. Direct least‐squares analysis of the measured peak shapes is used to calculate the interdiffusion coefficients. Equations are developed to describe dispersion in multicomponent systems containing arbitrary numbers of

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950203

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

年代:1991

数据来源: WILEY

摘要:

AbstractLiquid ethyliodide was studied by means of X‐ray diffraction experiments in order to investigate which type of intermolecular interaction determines the structure of the liquid state. The X‐ray diffraction studies of liquid ethyliodide were carried out at a wavelength of 1.54 Å. The data were corrected for polarization, absorption. Compton scattering and multiple scattering. The structure of the molecule was determined from the coherent distinct differential cross section. After subtraction of the intramolecular contribution a structure modelling technique was used to generate a model system which reproduces the Intermolecular cross section. The computed pair correlation functions of the model system were simulated by RISM calculations based on Lennard‐Jones interactions. The parameter values obtained by comparing the simulated atom pair correlation function with the model functions suggest the existence of strongly attractive interactions between the highly polarizable iodine

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950204

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe present new experimental data of the excess molar enthalpies at 298.15 K for eighteen different binary mixtures of nine methyl alkanoates (ethanoate to decanoate) with n‐heptane and n‐undecane. The results show that all the systems are endothermic,hEvalues increase with the length of the n‐alkane and decrease with the length of the methyl ester. The data have been analysed with a version of the UNIFAC model, and the parameters corresponding to the CH2/COOC interaction have been recalculated using a larger base of experimental data. New values for the CH2/COO interaction parameters have been obt

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950205

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe molecular origin of the negative thermal expansion of fluids has been studied for the one‐dimensional system with nearest‐neighbor interactions. ThePLTbehavior accompanying the negative thermal expansion is demonstrated for two model potential functions: Added to the hard core repulsive force, Model I has a truncated power potential function and Model II has a step potential function. In Model II, the negative thermal expansion is accompanied by the positive thermal expansion in the lower temperature region, i. e. the length of the system has the maximum and the minimum with increasing the temperature at constant pressure in Model II. Peculiar thermodynamical behavior of Model II is ascribed to the thermal transition between two molecular states, which is simulated by the mixture model of fluids. – The negative thermal expansion is analyzed on the basis of the theory of thermal fluctuation: The thermal expansion of length is composed of two terms due to the correlation between the internal energy and the length and the autocorrelation of the length, respectively. The negative thermal expansion is brought about by the negative correlation between the internal energy and the length, and the system shows a large fluctuation within and around the region of the negative thermal expansion. Since the attractive interaction reduces the fluctuation of the length, the attractive interaction enlarges the region of the negative thermal expansion in cooperation with soft‐repulsive interactions. Present results on the one‐dimensional system reproduce the essential feature of the negative thermal expansion in the real systems such as water or liquid

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950206

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

年代:1991

数据来源: WILEY

摘要:

AbstractMolar excess enthalpiesHEhave been measured for ternary mixtures of methanol + MTBE + n‐heptane and for the three corresponding binary mixtures of these compounds using a quasi‐isothermal flow calorimeter. The measurements have been performed at atmospheric pressure and at 298.1 and 313.1 K. The experimental results are compared with those calculated using the ERAS‐(Extended Real Associated Solution) model and the NRTL‐e

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950207

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

年代:1991

数据来源: WILEY

摘要:

AbstractMixed solutions of the anionic surfactant Sodiumdodecylsulfate (SDS) and the zwitterionic Tetradecyldimethylaminoxid (TDMAO) were studied under shear in a Couette‐type apparatus. For shear rates exceeding a critical shear gradient γcthe solutions show birefringence which approaches a constant value ΔnMAXwith increasing shear rate. At the same time properties like the shear viscosity and the normal stress difference increase dramatically. A structural modification must thus have taken place for γ>γc: a shear‐induced structure (SIS) has developed. – The structure of the micelles in the solution at rest was determined by SANS‐, electric birefringence‐ and viscosity experiments for different mixing ratios, concentrations and ionic strength. The solutions under shear were studied by SANS, flow‐birefringence and rheological measurements. – At rest small, rodlike micelles which consist of mixed surfactants are present. The length of the micelles are smaller than their mean distance and the viscosity is low in this case. The dimensions of the micelles were determined from the positions of the correlation peaks in the SANS‐patterns which are due to repulsive forces between the charged aggregates. At a mixing ratio of 9:1 (TDMAO:SDS;C= 100 mM) the solutions are viscoelastic and no SIS is detected. The SIS is thus formed only in solutions with surfactant concentrations which are below the overlap concentration. At γc– at which the SIS is beginning to form – the product of γcand τROT, the rotational relaxation time of the rods, is much smaller than one. – As soon as a critical shear gradient is reached these former isotropic micellar solutions show birefringence, an extinction angle of zero degrees, normal stress difference and an increased viscosity. Former isotropic SANS‐patterns deform and peaks show the appearence of a highly ordered structure in equilibrium with unordered micelles. All micelles taking part in the SIS are completely aligned in the direction of flow. Formation of the SIS is highly dependent on concentration, mixing ratio and ionic strength. Finally, two proposals for the nature of SIS are presented: A shear induced phase transition into domains of (pseudo)nematic phases seems most likely to us and is consistent with our experimental results. But also a pearl‐string like array in domains of

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950208

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

年代:1991

数据来源: WILEY

摘要:

AbstractCathodic hole injection by Fe(CN)63‐ions was observed at mechanically damaged, i.e. dislocation containing, p‐Si electrodes in contact with aqueous electrolytes. The injection current was observed to start at a potential corresponding to a substantial band bending and to reach a saturation region. In that saturation region the current density was somewhat less than linearly dependent on the Fe(CN)63‐concentration and increased with increasing depth of damage, i.e. average depth of dislocations. The observations could be explained by a model in which it was assumed that the dislocations behave as micro‐electrodes with hole injection limited by Fe(CN)63‐diffusion to the electrodes. The holes are then conducted along the dislocation lines to where tunneling to the valence band becomes

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950209

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

年代:1991

数据来源: WILEY

摘要:

AbstractFrom ellipsometric measurements, combined with surface analysis by SEM, Auger spectroscopy and X‐ray diffraction, it appears that a porous arsenic layer develops upon the p‐type gallium arsenide electrode surface in acid, aqueous indifferent electrolyte solution during anodic current flow. Due to its porosity, this layer does not affect the forward current‐potential characteristics of the electrode. Also under open‐circuit circumstances in the same electrolyte, the arsenic layer appears to grow. The probable reactions corresponding to both arsenic deposition processes are di

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950210

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

年代:1991

数据来源: WILEY