Dynamic mobility of spherical colloidal particles in concentrated suspensions: moderately thick double layers

A simple approximate expression is derived for the dynamic electrophoretic mobility mu Of spherical colloidal particles in concentrated suspensions in an applied oscillating electric field. This expression is applicable when the particles have low zeta potentials, very low relative permittivity and moderately thick double layers. It is found that the present approximation produces the correct dependence of the mobility magnitude on the particle volume fraction phi. That is, the mobility magnitude exhibits a maximum when plotted as a function of phi, in contrast to the case of infinitesimally thin double layers, in which case the mobility magnitude increases as phi increases, showing no maximum. (C) 1999 Elsevier Science B.V. All rights reserved.