On the molecular theory of aqueous electrolyte solutions. IV. Effects of solvent polarizability

Abstract

This paper describes a new level of theory with which to study model electrolyte solutions with a polarizable solvent. The theory considers the average local electric field experienced by a solvent particle as a function of its separation, R, from an ion and is referred to as the R-dependent mean-field (RDMF) approximation. Explicit expressions are derived for model solutions consisting of hard-sphere ions immersed in a hard polarizable dipole tetrahedral-quadrupole solvent. The lateral solvent fields are shown to cancel a large portion of the field generated by the ionic charge. The RDMF gives rise to an effective spherical ion–solvent potential which will affect the low-concentration limiting behavior of certain thermodynamic properties. The reference hypernetted-chain (RHNC) approximation is solved to obtain RDMF/RHNC results at infinite dilution and low concentration for several model aqueous electrolyte solutions. The ion–ion correlations and thermodynamic quantities such as the mean activity coefficient and partial molar volume of the solute are found to be particularly sensitive to the treatment of the solvent polarizability as this level.