Some common problems concerning solvent polarization and dielectric behaviour at ions and electrode interfaces

Abstract

The sensitivity of the dependence of ionic hydration properties of simple cations and anions on ionic radius is compared and related to the dielectric polarization in the solvent, near the ion. Corresponding dielectric polarization of the water solvent in the interphase at the surface of charged electrodes is evaluated on the basis of several models of oriented water dipoles at electrodes and compared with the situation at ions. It is pointed out that previous theories of the double-layer at electrodes have considered either the solvent polarization in the absence of adsorbed ions or the behaviour of ions independently of the solvent polarization by the electrode surface charge. Calculations are given that indicate that the surface concentrations of adsorbed ions at electrodes are commonly sufficient to cause a major influence on the behaviour of interphasial water in addition to that arising from the effect of electrode surface charge. Further, repulsion, due to overlap of Gurney cospheres of ions, will be an important factor in ionic interactions laterally within the double-layer.