Dynamic mobility of particles with thick double layers in a nondilute suspension

The dynamic mobility of a nondilute suspension of spherical particles is in vestigated in the case where the thickness of the electrical double layer a round each particle is comparable to the particle radius. A formula is obta ined for the O(phi) correction in a random suspension of particles with vol ume fraction phi, involving an integral over the dynamic mobility of a pair of spheres, This formula is then evaluated using both analytical approxima tions and numerical results previously obtained for the pair mobilities and valid for low surface potentials. The effect of double-layer thickness on the O(phi) coefficient is most pronounced at low frequencies, and lessens o nce the hydrodynamic penetration depth is smaller than the particle radius. Various approximations are considered that use the O(phi) result to predic t the dynamic mobility in concentrated suspensions, and at high frequencies these approximations are shown to give results qualitatively different fro m those of recent cell models. (C) 2000 Academic Press.