  We study the electrophoretic mobility of spherical charged colloids in a
low-salt suspension as a function of the colloidal concentration. Using an
effective particle charge and a reduced screening parameter, we map the data
for systems with different particle charges and sizes, including numerical
simulation data with full electrostatics and hydrodynamics and experimental
data for latex dispersions, on a single master curve. We observe two different
volume fraction-dependent regimes for the electrophoretic mobility that can be
explained in terms of the static properties of the ionic double layer.
