Self-diffusion coefficients of charged particles: Prediction of nonlinear volume fraction dependence

We report on calculations of the translational and rotational short-time self-diffusion coefficients D-s(t) and D-s(t) for suspensions of charge-stabilized colloidal spheres. These diffusion coefficients are affected by electrostatic forces and many-body hydrodynamic interactions (HI). Our computations account for both two-body and three-body HI. For strongly charged particles, we predict interesting nonlinear scaling relations D-s(t) proportional to 1-a(t) phi(4/3) and D-s(r) proportional to 1-a(r) phi(2) depending on volume fraction phi, with essentially charge-independent parameters a(t) and a(r). These scaling relations are strikingly different from the corresponding results for hard spheres. Our numerical results can be explained using a model of effective hard spheres. Moreover, we perceptibly improve the known result for D-s(t) of hard-sphere suspensions.