Calculation of the electrochemical contribution to the interaction between charged plates

Abstract

Numerical procedures are developed for calculating in a general way outlined previously the electrochemical contribution to the free energy of interaction between dissimilar charged plates in electrolyte solutions of any valence type.

Calculations of interactions between model acidic and amphoteric surfaces are used to show that these procedures are satisfactory. Their application to vitreous silica and goethite surfaces indicate that the charge on the solid side of the plane of shear increases as the plate separation decreases for vitreous silica in 10^–4 molar KNO₃ and for goethite in 10^–4 molar NaCl.

The implications of this finding in modelling such surfaces are considered. It could be that the plane of shear moves closer to the solid surface as the plate separation is decreased. The method of Bell and Peterson for calculating free energies of interaction is shown to be general.