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 Dₛᵗ and Dₛʳ 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 Dₛᵗ∝1-aₜφ4/3 and Dₛʳ∝1-aᵣφ² depending on volume fraction φ, with essentially charge-independent parameters aₜ and aᵣ. 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 Dₛᵗ of hard-sphere suspensions.