  The transport of polyelectrolytes confined by oppositely charged surfaces and
driven by a constant electric field is of interest in studies of DNA separation
according to size. Using molecular dynamics simulations that include surface
polarization effect, we find that the mobilities of the polyelectrolytes and
their counterions change non-monotonically with the confinement surface charge
density. For an optimum value of the confinement charge density, efficient
separation of polyelectrolytes can be achieved over a wide range of
polyelectrolyte charge due to the differential friction imparted by the
oppositely charged confinement on the polyelectrolyte chains. Furthermore, by
altering the placement of the charged confinement counterions, enhanced
polyelectrolyte separation can be achieved by utilizing surface polarization
effect due to dielectric mismatch between the media inside and outside the
confinement.
