An atomistic study of a poly(styrene sulfonate)/ poly(diallyldimethylammonium) bilayer: The role of surface properties and charge reversal

In this work, we present the first molecular dynamics simulation on the formation of a polyelectrolyte bilayer resolved in atomistic detail, extending a previous study of the adsorption of poly(styrene sulfonate) [B. Qiao, J. J. Cerdà and C. Holm, Macromolecules, 2011, 44, 1707-1718.] to the formation of a poly(styrene sulfonate)/poly(diallyldimethylammonium) bilayer. Extensive molecular dynamics simulations of the adsorption process on different substrates (hydrophilic/hydrophobic, charged/neutral) were performed. Our results seem to indicate that a high enough surface charge density (0.164 C m^-2 here) may be required to achieve a multilayer linear growth in the framework of the electrostatic driven mechanism for PEM growth. We furthermore demonstrate that the use of stiff hydroxyl groups for creating a hydrophilic surface from a hydrophilic one can lead to severe simulation artifacts, and we discuss a simple remedy for this problem.