Short-time dynamics and sedimentation of charge-stabilized suspensions

In this work, we discuss the combined effects of the electrostatic and hydrodynamic interaction (HI) on the short-time dynamics and the sedimentation velocity of charge-stabilized suspensions. For this purpose the measurable hydrodynamic function H(q) is calculated by using two methods based, respectively, on a renormalized density fluctuation expansion, and on a pairwise-additivity approximation of the hydrodynamic mobility tensors. It is shown that H(q) can deviate considerably from the free diffusion coefficient, D 0, for systems of volume fractions Φ as low as 10−3, and that these effects are more pronounced for collective diffusion than for self-diffusion. For deionized suspensions, the sedimentation coefficient, H(0)/D 0, and the short-time self-diffusion coefficient, D s,short, are found at low Φ to scale, respectively, as Φ 1/3 and Φ 4/3. Furthermore, we analyze the dependence of H(0) and D s,short on the amount of added electrolyte.