  We study the combined effects of electrostatic and hydrodynamic interactions
(HI) on the short-time dynamics of charge-stabilized colloidal spheres. For
this purpose, we calculate the translational and the rotational self-diffusion
coefficients, $D^t_s$ and $D^r_s$, as function of volume fraction $\phi$ for
various values of the effective particle charge $Z$ and various concentrations
$n_s$ of added 1--1 electrolyte. Our results show that the self-diffusion
coefficients in deionized suspensions are less affected by HI than in
suspensions with added electrolyte. For very large $n_s$, we recover the
well-known results for hard spheres, i.e. a linear $\phi$-dependence of $D^t_s$
and $D^r_s$ at small $\phi$. In contrast, for deionized charged suspensions at
small $\phi$, we observe the interesting non-linear scaling properties
$D^t_s\propto1-a_t\phi^{4/3}$ and $D^r_s\propto 1-a_r\phi^2$. The coefficients
$a_t$ and $a_r$ are found to be nearly independent of $Z$. The qualitative
differences between the dynamics of charged and uncharged particles can be well
explained in terms of an effective hard sphere (EHS) model.
