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

Abstract

We report on calculations of the translational and rotational short-time self-diffusion coefficients $D_s^t$ and $D_s^r$ 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 $D_s^t\propto 1-a_t{\varphi }^{4/3}$ and $D_s^r\propto 1-a_r{\varphi }^2$ depending on volume fraction $\varphi$, 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.

8 pages, LaTeX, 3 Postscript figures included using epsf

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