Ion adsorption and equilibrium distribution of charges in a cell of finite thickness

Abstract

By using a self-consistent method the equilibrium distribution of charges in a liquid cell of finite thickness, when the adsorption phenomenon is present, is evaluated. The analysis is performed for the two limiting cases where the neutral density is fixed : either very weak (total dissociation), or very large (weak dissociation). The surface adsorbed charge is evaluated, by extending the classical Langmuir problem of adsorption to the case far from the saturation regime. The importance of the considered problem on the interfacial properties of liquid is discussed. In particular it is shown that by taking into account the surface electric field associated with the adsorbed charges, a non-local character of the anisotropic part of the anchoring energy of liquid crystals is expected. This agrees with recent experimental observations showing that nematic samples of different thicknesses, but with the same surface treatment, seem to have different anchoring energies.