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Effects of ion solvation on phase equilibrium and interfacial tension of liquid mixtures

Wang, Rui and Wang, Zhen-Gang (2011) Effects of ion solvation on phase equilibrium and interfacial tension of liquid mixtures. Journal of Chemical Physics, 135 (1). Art. No. 014707. ISSN 0021-9606.

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We study the bulk thermodynamics and interfacial properties of electrolyte solution mixtures by accounting for electrostatic interaction, ion solvation, and inhomogeneity in the dielectric medium in the mean-field framework. Difference in the solvation energy between the cations and anions is shown to give rise to local charge separation near the interface, and a finite Galvani potential between two coexisting solutions. The ion solvation affects the phase equilibrium of the solvent mixture, depending on the dielectric constants of the solvents, reflecting the competition between the solvation energy and translation entropy of the ions. Miscibility is decreased if both solvents have low dielectric constants and is enhanced if both solvents have high dielectric constant. At the mean-field level, the ion distribution near the interface is determined by two competing effects: accumulation in the electrostatic double layer and depletion in a diffuse interface. The interfacial tension shows a nonmonotonic dependence on the salt concentration: it increases linearly with the salt concentration at higher concentrations and decreases approximately as the square root of the salt concentration for dilute solutions, reaching a minimum near 1 mM. We also find that, for a fixed cation type, the interfacial tension decreases as the size of anion increases. These results offer qualitative explanations within one unified framework for the long-known concentration and ion size effects on the interfacial tension of electrolyte solutions.

Item Type:Article
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Wang, Zhen-Gang0000-0002-3361-6114
Additional Information:© 2011 American Institute of Physics. Received 30 April 2011; accepted 10 June 2011; published online 7 July 2011. This work is in part supported by the National Science Foundation through MRSEC-CALTECH.
Funding AgencyGrant Number
Subject Keywords:dielectric liquids, electrolytes, electrostatics, liquid mixtures, permittivity, phase equilibrium, solubility, solvation, surface tension, thermochemistry
Issue or Number:1
Classification Code:PACS: 82.45.Gj; 82.60.Lf; 64.75.Cd; 64.75.Ef; 68.03.Cd; 77.22.Ch
Record Number:CaltechAUTHORS:20110804-092317279
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Official Citation:Effects of ion solvation on phase equilibrium and interfacial tension of liquid mixtures Rui Wang and Zhen-Gang Wang J. Chem. Phys. 135, 014707 (2011); doi:10.1063/1.3607969 (11 pages) Online Publication Date: 7 July 2011
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24674
Deposited By: Ruth Sustaita
Deposited On:04 Aug 2011 16:48
Last Modified:03 Oct 2019 02:58

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