A theoretical study of the solid–electrolyte solution interface. I. Structure of a hard sphere ion–dipole mixture near an uncharged hard wall

Abstract

In this paper we investigate the density and orientational structure of a molecular model electrolyte solution consisting of a mixture of charged hard spheres in a dipolar hard sphere solvent, located in the vicinity of a neutral hard wall. The electrolyte is symmetrically charged and all particles have the same size. The statistical mechanical treatment is the reference hypernetted-chain (RHNC) approximation for the bulk fluid and, respectively, the linearized RHNC (LRHNC) and the full RHNC approximations for the wall–molecule and the wall–ion correlation functions. Our results for the pure solvent are in good agreement with previous theoretical work and available computer simulations. It is found that in addition to the steric effects due to the molecular solvent, image forces play an essential role in the determination of the ionic density profile near the wall. Moreover, at moderate ionic concentrations, our results indicate that beyond the first layer of solution this electrostatic effect may be well described by a continuum description of the solvent.