Collapse of polyelectrolyte brushes in electric fields

Abstract

We predict the collapse of a polyelectrolyte brush grafted on an electrode that is induced by applied electric fields for the limiting cases of low and high salt concentrations. The polyelectrolyte brush collapses locally to screen the charges induced on the electrodes. For low salt concentrations, the height of the polyelectrolyte brush decreases steeply with increasing the voltage between the electrodes because the number of counterions expelled from the brush increases exponentially. However, when the system is in equilibrium with monovalent salts at high concentrations, the brush height decreases almost linearly with increasing the voltage instead of the steep collapse. This is because the voltage drop mainly occurs over the diffuse double layer associated with the distant electrode. Copyright (C) EPLA, 2011