ELECTRICAL DOUBLE-LAYER INTERACTION BETWEEN DISSIMILAR SPHERICAL COLLOIDAL PARTICLES AND BETWEEN A SPHERE AND A PLATE - NONLINEAR POISSON-BOLTZMANN THEORY

Recently the double layer forces and interaction free energies between spherical colloidal particles, according to the Poisson-Boltzmann equ ation, have been accurately calculated by us and others. In this paper we conclude our investigations in this area by extending the calculat ion of double layer interactions to unequal spherical particles. We al so consider the case of a sphere and a plate, a geometry relevant to a tomic force microscope measurements when a colloidal particle is attac hed to the cantilever tip. We compare the results against those of the linearized Poisson-Boltzmann equation and the Deryaguin approximation over a wide range of conditions. The Deryaguin approximation is found to be highly accurate for the force in sphere/plate geometry and acce ptably so for dissimilar spheres under typical colloidal conditions. W e conclude with comments on the double layer forces acting on a bare a tomic force microscope tip.