Strongly Stretched Polyelectrolyte Brushes

Using molecular dynamics simulations, we study completely and partially charged polyelectrolyte brushes. Counterions are treated explicitly. At weak electrostatic interaction we find that the collapsed brush regime obtained at strong interaction disappears. The chains become strongly stretched perpendicular to the grafting surface. Contrary to the well-known scaling law for the osmotic brush regime which gives a thickness, independent of grafting density, we obtain a weak, but nonvanishing, dependence. This unusual result is in agreement with the behavior in the nonlinear osmotic brush regime recently predicted on the basis of an extended theoretical model which includes the lateral inhomogeneity of counterion distribution.