Molecular solvent model for an electrical double layer: Reference hypernetted chain results for potassium chloride solutions

Abstract

The reference hypernetted-chain theory is solved for the structure of the double layer at the surface of large spherical macroions in a wholly molecular model of aqueous KCl. Detailed results are reported for the solvent and ionic structure throughout the double layer for surface charges up to 0.175 C m−2 and salt concentrations of 0.1 to 1.0 M. Concentration effects on the short-range structural features of the interface are discussed and related to the behavior of the same model at infinite dilution. There is a very rapid neutralization of the surface charge by a Coulombic adsorption of counterions into a narrow region near contact beyond which the system responds as though to a much lower effective surface charge. The relationship of these results to the properties of continuum solvent models and the implications for the electrostatic potential and differential capacitance of the double layer are discussed.