A Molecular Dynamics Study of Two Apposing Polyelectrolyte Brushes with Mono- and Multivalent Counterions

The conformational characteristics of polyelectrolytes end-grafted on two apposing walls are studied. The monovalent and multivalent counterions are explicitly treated. It is found that the polyelectrolyte brushes undergo a collapse transition in the presence of multivalent counterions at large wall separations. Moreover, the brush thickness is linearly proportional to the grafting density and independent of the counterion valence. The effects of normal compression on the density profiles of monomers and counterions, the pressure, the net charge density and the degree of interpenetration are also studied. The density profiles of counterions exhibit an asymmetrical distribution in systems with a mixture of monovalent and trivalent counterions.