Polarizability effects in the electrostatic repulsion between charged colloidal particles

Abstract

The electrostatic interaction between two colloidal spheres with a fixed surface charge density is calculated in order to determine the influence of the polarizability of the spheres on the repulsive electrostatic force. The linearized form of the Poisson—Boltzmann equation is used in combination with the Laplace equation, which enables us to construct an exact solution in terms of a multipole expansion. The calculations show clearly how the electrostatic force decreases with the polarizability of the particle, the decrease becoming larger with stronger double layer overlap, whereas it is relatively insensitive to κ a. This insensitivity is a consequence of tangential screening effects inside the particles, as illustrated by a comparison of the exact solution with a Derjaguin-type approximation in which the possibility of tangential screening is not included. It is pointed out that for slowly coagulating dispersions of particles with a fixed surface charge density, the stability ratio W is sensitive to the polarizability of the particle.