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  • 1
    Electronic Resource
    Electronic Resource
    Phase instabilities in charged hard-sphere mixtures. I. Binary mixtures of salt and hard spheres (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8098-8110 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this series of two papers we investigate phase instabilities in charged hard-sphere mixtures. Here, we derive general expressions for the thermodynamic properties of a common anion mixture and apply these to study phase separation in mixtures of salt and hard spheres. Excess thermodynamic properties due to Coulombic interactions are obtained using the analytical solutions for the mean spherical approximation closure. A detailed description of the dependence of the resulting phase diagrams on charge asymmetry of the ions, size of the neutral species, and the osmotic pressure of the mixture is presented. Binary mixtures of salt and hard spheres exhibit type III phase behavior. An increase in charge asymmetry results in an increase in the critical temperature of the mixture because enthalpic forces (ion-pairing) dominate. An increase in the size of the neutral species also results in an increase in the critical temperature of the mixture because of packing effects, which encourage phase separation. Potential applications of the model to experimental systems are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470174
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  • 2
    Electronic Resource
    Electronic Resource
    Phase instabilities in charged hard-sphere mixtures. II. Binary mixtures of salts (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 8111-8123 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Charged hard-sphere mixtures consisting of two positively charged species and one negatively charged species (common anion mixtures) are used to represent binary mixtures of salts. Phase separation in the mixture is studied using the Gibbs free energy expression for common anion mixtures derived in paper I of this series. A detailed description of the dependence of the resulting phase diagrams on molecular size and charge of the species, and on the osmotic pressure of the mixture is presented. Binary mixtures of salts containing equal-sized ions exhibit type III phase behavior whereas binary mixtures of salts containing ions of unequal size exhibit either type II or type IV phase behavior. The type of phase behavior observed in binary mixtures of salts is characterized as a function of the critical pressures and critical volumes of the pure salts. Our results suggest that phase separation in mixtures of charged hard spheres is influenced by a competition between mixing effects (entropy), which encourage miscibility and ion-pairing effects (enthalpy), which encourage phase separation. Potential applications of the model to experimental systems are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470175
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  • 3
    Electronic Resource
    Electronic Resource
    Modeling of phase separation in PEG-salt aqueous two-phase systems (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 3508-3522 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A molecular model based on the integral equation theory of statistical thermodynamics is used to study phase separation in PEG-salt aqueous two-phase systems. PEG molecules are modeled as hard spheres that attract each other through a temperaturedependent Yukawa potential, which mimics the effect of PEG-water hydrogen bonding on the attraction between PEG molecules. The salt ions are modeled as charged hard spheres interacting through a Coulombic potential. Excess thermodynamic properties due to Coulombic and Yukawa interactions are calculated by analytical solutions to the Ornstein-Zernike equation for the mean spherical approximation closure. Yukawa parameters for PEG-PEG interactions are determined by fitting the theoretical phase diagram for a pure Yukawa fluid to the experimental phase diagram for a PEG-water mixture. The model predicts experimentally observed trends: increasing the temperature increases the slope and length of the tie lines; increasing the PEG molecular weight increases the miscibility gap; and increasing the anion charge lowers the salt concentration at which phase separation occurs. Theoretical results allow us to infer the relative importance of ion-PEG interactions, ion-solvent interactions, and the interpenetrable nature of PEG molecules on the phase separation in PEG-salt aqueous two-phase systems.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690421220
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    Paper (German National Licenses)
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