SHORT-TIME DYNAMICS OF CHARGE-STABILIZED COLLOIDAL SUSPENSIONS

We have calculated the combined effects of the electrostatic and hydrodynamic interactions on the short-time dynamics of charge-stabilized colloidal suspensions, which can be investigated experimentally from the first cumulant of the dynamic scattering function. The first cumulant is obtained using two methods, a pairwise-additivity approximation for the many-body hydrodynamic interaction combined with a far-field expansion of the mobility tensors, and a renormalized density fluctuation expansion due to Beenakker and Mazur. An effective hard-sphere model is employed to provide a simple physical interpretation of the results derived from both methods. It is shown that even for moderately charged colloidal particles the hydrodynamic interaction cannot be neglected, and that its effects are more pronounced for collective diffusion than for self-diffusion. Moreover, our calculations predict a non-analytic volume fraction dependence of the sedimentation velocity, with an exponent whose numerical value is sensitive to the amount of added electrolyte.