Shear of a planar polyelectrolyte brush

The behavior of a planar polyelectrolyte brush subjected to normal and tangential external forces is considered. A new “polyelectrolyte effect” is predicted: shear of a free polyelectrolyte brush leads to a decrease in brush thickness contrary to the case of a free neutral brush. Such behavior is equivalent to that of a neutral brush subjected to an external normal stretching force. In the case of a polyelectrolyte brush this force is created by the osmotic pressure of mobile counterions neutralizing grafted chain charges. Addition of salt diminishes the polyelectrolyte effect and changes the sign of correlation between brush thickness and tangential deformation.