We Studied theoretically the effect of grafted polymer layers on electro-os
motic solvent flows. This allowed us to predict qualitative features of the
electrophoretic mobility of charged particles on which small polymers (cha
rged or neutral) have been grafted. The cases of sparse and dense grafting
were both analyzed, accounting for the deformation of the grafted polymers
by the electrically induced hydrodynamic flow generated by the charged comp
osite surface. For sparsely grafted polymers, we derived an expression for
the modification of the effective electro-osmotic mobility mu (eff) of the
polymer-bearing surface in terms of the density and conformation of the gra
fted chains. Sufficiently strong electric fields modify the conformation of
the grafted chains, resulting in a nonmonotonic dependence of mu (eff) on
electric field strength. For densely grafted polymers, the electro-osmotic
behavior of the system is dominated by the electrophoretic properties of th
e polymer. In the limit of very high electric fields, the inner region of t
he polymer layer is deformed by the electro-osmotic flow, resulting in enha
nced screening of electro-osmotic flows by the polymer layer.