  Computer simulations are used to investigate the response of a charged
colloid and its surrounding microion cloud to an external electric field. Both
static fields (DC) and alternating fields (AC) are considered. A mesoscopic
simulation method is implemented to account in full for hydrodynamic and
electrostatic interactions. The response of the system can be characterized by
two quantities: the mobility and the polarizability. Due to the interplay of
the electrostatic attraction and hydrodynamic drag, the response of the
microions close to the colloid surface is different from that of the microions
far away from the colloid. Both the mobility and polarizability exhibit a
dependency on the frequency of the external fields, which can be attributed to
the concentration polarization, the mobility of the microions, and the inertia
of microions. The effects of the colloidal charge, the salt concentration, and
the frequency of the external fields are investigated systematically.
