Double-layer effects at the surface of a molten salt

Abstract

Results of calculations concerning the charge distribution within the liquid–vapour interface of the primitive model of a molten alkali halide are presented. In this model the anion and cation are represented by hard spheres of different diameters; there is as a result an electrical double layer at the interface. A perturbation theory is developed which connects the surface properties of the alkali halide to those of a closely related system in which charge separation cannot occur and which can in principle be solved by methods which are presently available. The effect of charge separation on the magnitude of surface tension is calculated. The magnitude of the dipole layer at the interface is calculated for a number of molten salts using a sum rule which has been derived previously. In general it is found that the larger species preferentially sits on the vapour side of the interface.