Short-time dynamics and sedimentation of charge-stabilized suspensions

Abstract

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.