Molecular solvent model for an electrical double layer: Effects of ionic polarizability

The effect of ionic polarizability on properties of the electrical double layer is considered by extending a theory of Kusalik and Patey [J. Chem. Phys. 92, 1345 (1990)] to the case of an ion at a distance r from a charged macroion. The reference hypernetted-chain theory is solved for a fully molecular model of the double layer and the results are compared with previous results for an identical model without polarizability and with experimental data for double layers in alkali halide solutions. Polarizability is found to have a large effect on the differential capacitance at high surface charges and to make a substantial contribution to the experimentally observed asymmetry in this quantity. This effect is shown to have its origin, not in any structural change in the double layer, but in the contribution to the potential from the induced polarization of the ions themselves.