Double layer interaction of two charged colloidal spherical particles of a concentrated dispersion in a medium of low dielectric constant. Part 4.—Conducting particles in contact

Abstract

A concentrated suspension of identical charged spherical colloidal particles in a hydrocarbon medium is considered. The concentration of counter-ions in the hydrocarbon, which are of one species, is assumed to be so small that their mean volume density is virtually uniform. The effect of surrounding particles on any two neighbouring particles is accounted for by enclosing these two particles by a symmetrical surface S₀ on which the normal derivative of the potential vanishes everywhere. The volume enclosed by S₀ equals twice the mean volume per particle. The potential in the hydrocarbon medium satisfies Poisson's equation, an exact solution of which is obtained in terms of tangent-sphere coordinates at particle contact, assuming that the particle surfaces are equipotentials. The electric double layer force between two particles in contact is calculated by using the Maxwell electrostatic stress tensor. It is suggested that, in hydrocarbon media, electric double layer forces are not significant in determining colloid stability.