Charged colloids nearinterfaces

Abstract

This article deals with the electric double-layer force between acharged colloidal sphere and a charged dielectric planar wall. Tointroduce the problem and to uncover the basic physicsinvolved, we start by first reviewing the effective wall-colloidpotentials that one obtains in linearized Poisson-Boltzmanntheory. The important key concepts in this context are: chargerenormalization, confinement effects, salty interfaces, andimage-charge effects due to the dielectric discontinuity at thewall. Starting from the potentials derived in linear theory, wethen come to approximate wall-colloid potentials that are validalso in the parameter regime where the non-linearity of thePoisson-Boltzmann equation becomes important. The range ofvalidity of these potentials is systematically investigated bycomparing them with potentials based on the exact numericalsolution to the Poisson-Boltzmann equation. The important parametersof the calculation are the salt content of the electrolyticsolution, the colloidal sphere radius, and the surface chargedensities on both the wall and the colloid. We then brieflydiscuss what additional effect a concentrated suspension ofsuch colloidal spheres has on the interfacial colloid, and closewith a short report of an optical experiment that has recentlybeen performed to measure the approximate wall-colloid potentialsinvestigated here.