Density Profile of Polyelectrolyte Brushes

Using small angle neutron scattering techniques, we have determined the interfacial density profile of polyelectrolyte brushes. We show that in pure water the density profile has a Gaussian shape whose characteristic length appears to be a decreasing function of the grafting density. Upon the addition of salt, the layers shrink but never collapse. Even at very high ionic strength, the chains remain stretched and the density profile is eventually parabolic.