Screened electrostatic interactions between clay platelets

An effective pair potential for systems of uniformly charged lamellar collo ids in the presence of an electrolytic solution of microscopic co- and coun terions is derived. The charge distribution on the discs is expressed as a collection of multipole moments, and the tensors which determine the intera ctions between these multipoles are derived from a screened Coulomb potenti al. Unlike previous theoretical studies of such systems, the interaction en ergy may now be expressed for discs at arbitrary mutual orientation. The po tential is shown to be exactly equivalent to the use of linearized Poisson- Boltzmann theory.