SHORT-TIME DYNAMICS OF CHARGE-STABILIZED COLLOIDAL SUSPENSIONS

We have calculated the combined effects of the electrostatic and hydro dynamic interactions on the short-time dynamics of charge-stabilized c olloidal suspensions, which can be investigated experimentally from th e first cumulant of the dynamic scattering function. The first cumulan t is obtained using two methods, a pairwise-additivity approximation f or the many-body hydrodynamic interaction combined with a far-field ex pansion of the mobility tensors, and a renormalized density fluctuatio n expansion due to Beenakker and Mazur. An effective hard-sphere model is employed to provide a simple physical interpretation of the result s derived from both methods. It is shown that even for moderately char ged colloidal particles the hydrodynamic interaction cannot be neglect ed, and that its effects are more pronounced for collective diffusion than for self-diffusion. Moreover, our calculations predict a non-anal ytic volume fraction dependence of the sedimentation velocity, with an exponent whose numerical value is sensitive to the amount of added el ectrolyte.