摘要:

AbstractResults of small angle neutron scattering experiments with four solutions of the nonionic surfactant C12E5in D2O with critical and noncritical compositions in the vicinity of the lower critical point are reported (1.11·10−4≤x≤ 2.042·10−3;x, mole fraction of C12E5;xc= 5.74·10−4, critical mole fraction). They were obtained at temperatures away from the liquid/liquid coexistence curve. The observed angular dependence of scattered neutron intensity is assumed to be caused by micelles formed by surfactant molecules. Two characteristic lengths Ξ1and Ξ2are calculated from the scattering profiles. Ξ1has a value of the order of 10 nm. It is attributed to the extension of noncritical concentration fluctuations. Ξ2has a value of the order of 1 nm and is attributed to the core of micelles. At constant temperature Ξ1decreases with increasing surfactant concentration, whereas at constant surfactant concentration it increases with increasing temperature weakly (compared with the divergence of the correlation length of local composition fluctuations approachingTc). ‐ A combination of light scattering and small angle neutron scattering data obtained with the system C12E5/water gives support to the assumption that in the vicinity of the lower critical point a continuous change will take place from a comparatively weak temperature dependence of the length characterizing the structure of the liquid to a strong temperature dependence of the correlation length of the critical concent

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990502

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

年代:1995

数据来源: WILEY

摘要:

AbstractExperimental results for thermodynamic properties of aqueous two‐phase systems of poly(ethylene glycol) and di‐potassium hydrogen phosphate with and without partitioning biomolecules (glycine, phenylalanine and lysozyme) are reported for temperatures between 277 and 333 K. The results are used to develop a semiempirical group‐contribution expression for the excess Gibbs energy of dilute aqueous solutions containing polymeric as well as ionic solutes. The model is applied to correlate some of the new experimental data, while other experimental results are used to test its ability for predicting the electrical potential difference between the coexisting phases, the partition coefficient of lysozyme and the influence of polymer molecular weight on the phase behaviour of aqueous two‐phase systems – a field where most previously known methods are often i

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990503

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

年代:1995

数据来源: WILEY

摘要:

AbstractA comparison of experimental diffusion coefficients in aqueous solutions of electrolytes with those calculated by Onsager‐Fuoss and Pikal theories is presented. The influence of the ion size parametera, “distance of closest approach” of ions, on the variation of diffusion coefficients with concentration is disc

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990504

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe calculation ofGmEfrom VLE measurements has been extended to multicomponent systems including those where chemical reactions can occur. For nuclide mixtures, the methods have to be adapted in order to take into account the similarity of the mixture's components and the pseudo‐multicomponent characteristics of a system with isotopic exchange. Bigeleisen's theory of isotope effects can then be used to calculate self‐exchange equilibrium constants in the liquid phase at low temperatures and the vapour pressure of partially substituted nuclides. The formalism is applied to some relevant cases, namely those of water and ammo

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990505

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

年代:1995

数据来源: WILEY

摘要:

AbstractDynamic light scattering experiments are carried out with aqueous solutions of poly(2‐vinylpyridine) quarternized to small extents with ethyl bromide and dissolved in an aqueous solution of KBr (molar mass,Mw= 3.14·105g mol−1;Mw/Mn= 2.24; degree of quarternization, αe; 0.079 ≤ αe≤ 0.461; electrolyte concentration,cs= 1·10−2c+,c+= 1 mol dm−3). Apparent diffusion coefficientsDapp(αe,c̄p) are calculated from the data (c̄p, polymer concentration (g dm−3)). They are plotted as a function of the reduced composition variable Λ= αecp*/cs(cp*, molar volume concentration of the repeat unit of the polymer backbone). For Λ<1 a fast and a slow diffusive process is found. In the literature such a behaviour has been reported for solutions of h

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990506

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

年代:1995

数据来源: WILEY

摘要:

AbstractDynamic light scattering experiments are carried out with aqueous solutions of poly(4‐vinylpyridine) completely quarternized with dodecyl bromide and ethyl bromide in varying ratios in the presence of salt (KBr; αd+ αe= 1; 0.010 ≤ αd≤ 0.192; αdis the degree of quarternization by dodecyl bromide and αethat with ethyl bromide). Apparent diffusion coefficientsDapp(αd,c̄p) are calculated from the data (c̄pis the polymer concentration expressed in g dm−3). They are plotted as function of the reduced concentration variable λ = (cp*/cs) as well as of the degree of quarternization by dodecyl bromide αdat constant values of λ (cp* is the molar volume concentration of the repeating unit forming the polymer backbone;csis the molar volume concentration of the added salt). The resulting curves indicate a characteristic change of the diffusive properties of the systems: For λ<1 a fast and a slow diffusive mode are detected. At a constant value of λ (λ ≈︁ 2.0) the appearance of a slow diffusive mode is induced by decreasing systematically αd(αd≤ 0.192; αd+ αe≈︁ 1). It is predicted that the location of the “transit

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990507

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe multistep cathodic reduction at high temperature of the oxygen molecule at the porous platinum/yttria stabilized zirconia solid electrolyte interface has been critically analyzed. Steady state polarization experiments showed that for very thin and very porous layers and oxygen mixtures containing 1% or more oxygen the rate of the overall process is apparently governed by the electrode/electrolyte interfacial diffusion of neutral and/or single ionized atoms. This process is probably fed by the formation of single ionized oxygen molecules at the electrolyte surface, particularly in the neighbours of the electrode/electrolyte/gas phase triple phase boundary. At lower oxygen partial pressures and/or for thicker and less porous metal layers the control is probably transferred to the interpores molecular diffusion. The adsorption of oxygen onto the metal surface, as a step for feeding the transport of reducible species to the triple phase boundary, looks hardly consistent with the evident increase of the overall reaction rate with temperature. The role of platinum, however, can not be confined as a pure electron supply. In fact, at very negative overvoltages it enters the process of morphological expansion of the triple phase boundary zone and likely affects the activity of the electrolyte in the primary process of oxygen ionosorption.

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990508

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

年代:1995

数据来源: WILEY

摘要:

AbstractWe studied the influence of ionic strength on the stoichiometric equilibrium ionization constant of water in KNO3at 25°C by applying the Pitzer equations to the activity coefficients for the species in equilibrium. Reported values for NaCl and KCl media are also analysed

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990509

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe extraction of Eu(III) from perchlorate medium by a chloroform solution of thenoyltrifluoroacetone (HTTA) and 18‐crown‐6 (18C6) was kinetically studied. The effect of the extractants concentration, interfacial surface area as well as other parameters affecting the rate of extraction was separately investigated. The effect of temperature was also studied and the thermodynamic functions were calculated. A mechanism of extraction of Eu(III) was proposed to account for the experimental resu

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990510

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe emission spectrum of [Cr(urea)6]I3single crystals excited under resonance condition into the zero phonon4A2g→ E1/2(2Eg) absorption line, which is inhomogeneously broadened from 14210 to 14240 cm−1, is recorded at 1.9 K. The vibrational sideband spectrum is shifted in a characteristic way, the spectral profile being changed only in some minor details. All features can be explained by energy transfer processes between majority and minority complex species which have small differences of transition energies in the crys

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990511

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

年代:1995

数据来源: WILEY