New electrostatic model for highly charged surfaces

Abstract

A new electrostatically self-consistent model for coulombic interactions near highly charged surfaces has been formulated. The model is based on electrostatic adsorption of counter-ions at the distance of closest approach. These adsorbed counter-ions are allowed to “bounce” up to a certain well-defined distance. Thus, there exists a region that is bounded by the bouncing distance and by the distance of closest approach, and from which the co-ions are expelled. This picture of the double layer arises from the self-consistent application of the Debye—Hückel theory of strong electrolytes and from the Manning idea of ion condensation. The model has so far given good prediction for four unrelated phenomena for which only “high” surface-charge density is a common denominator: the differential capacities at Hg/solution interfaces, the surface pressures of insoluble monolayers at oil/water interfaces, the activity coefficients of 2:2 electrolytes, and for the repulsions of two flat double layers.