On the molecular theory of aqueous electrolyte solutions. I. The solution of the RHNC approximation for models at finite concentration

Abstract

This paper describes a theoretical study of the thermodynamic, dielectric, and structural properties of model aqueous electrolyte solutions. The model considered consists of hard sphere ions immersed in a hard polarizable dipole tetrahedral–quadrupole solvent with water-like parameters. The calculations involve the solution of the reference hypernetted-chain (RHNC) approximation for ion–solvent mixtures at finite concentration and some details of the general method are discussed. The influence of the molecular polarizability of the solvent particles is treated at the self-consistent mean field (SCMF) level and, surprisingly, the mean dipole moment of the solvent is found to be nearly independent of the salt concentration. Numerical results are reported for model alkali halide solutions and other 1:1 electrolytes, and comparisons are made with experimental results at 25 °C. The agreement obtained between theory and experiment is variable depending upon the particular property and solution considered. In addition to the explicit numerical results for aqueous electrolytes several general analytical results are also given. The most interesting of these are expressions for the low concentration large separation limiting behavior of the ion–solvent and solvent–solvent radial distribution functions.