An analysis of electrophoresis of concentrated suspensions of colloidal particles

An analysis of the electrophoretic motion of charged colloidal particles in a concentrated suspension is developed to predict the electrophoretic mobi lity of the particles and the electrical conductivity of the suspension. Th e analysis is based on a unit cell model that takes into account particle-p article hydrodynamic interactions and includes relatively thick electric do uble layers. The fluid motion in the unit cell is treated by writing the re levant Navier-Stokes equation in terms of the stream function and vorticity . The governing equations were then solved by a finite-difference method. T he calculated electrophoretic mobilities are in agreement with prior analyt ical solutions for moderately concentrated suspensions, and the theory redu ces to the result of O'Brien and White for low to moderate zeta potentials and dilute suspensions and to the classical result of Smoluchowski for thin double layers and dilute suspensions. A parametric study shows that the el ectrical conductivity of the suspension relative to a free electrolyte solu tion is affected by the counterion to co-ion diffusivity ratio, the double- layer thickness, and the volume fraction of particles. For a dispersion of moderately charged particles (moderate zeta potentials) with thick double l ayers, the numerical model predicts the electrical conductivity in agreemen t with experimental values reported in the literature. (C) 1999 Academic Pr ess.