  We present an experimental study of short-time diffusion properties in
fluid-like suspensions of monodisperse charge-stabilized silica spheres
suspended in DMF. The static structure factor S(q), the short-time diffusion
function, D(q), and the hydrodynamic function, H(q), in these systems have been
probed by combining X-ray photon correlation spectroscopy experiments with
static small-angle X-ray scattering. Our experiments cover the full
liquid-state part of the phase diagram, including deionized systems right at
the liquid-solid phase boundary. We show that the dynamic data can be
consistently described by the renormalized density fluctuation expansion theory
of Beenakker and Mazur over a wide range of concentrations and ionic strengths.
In accord with this theory and Stokesian dynamics computer simulations, the
measured short-time properties cross over monotonically, with increasing salt
content, from the bounding values of salt-free suspensions to those of neutral
hard spheres. Moreover, we discuss an upper bound for the hydrodynamic function
peak height of fluid systems based on the Hansen-Verlet freezing criterion.
