Primitive electrolyte solutions around a charged colloid: density functional approach

Abstract

ABSTRACTWe have developed the density functional theory, which is based both on the modified fundamental-measure theory for the hard spheres and on the weighted-density approximation for the electrostatic residual contribution, for studying the structure of the size-symmetric and asymmetric electrolyte solutions around a charged hard colloid. The calculation shows that the present theory provides an excellent description of the primitive electrolyte solutions and indicates the suitability of the approximations used in the formalism. The preset theory provides better the structural results than the density functional theories based on the excess free energy functional expansion with respect to the bulk ionic density and the hypernetted-chain equation based on the mean spherical approximation over a wide range of colloid sizes, ion concentrations and valence of a colloid. We have confirmed that the present theory is able to predict the phenomena of charge reversal and overcharging occurring near a colloidal interface, in agreement with previous primitive model Monte Carlo simulations and theoretical studies reported in the literature.