Coarse grained molecular dynamics simulations of polystyrene sulfonate (PSS) brushes

Polyelectrolytes grafted to surfaces are useful materials for sensors, chemical separation, and biomedical devices. In this computational study, we are focused on understanding one such surface-grafted polyelectrolyte, namely, polystyrene sulfonate (PSS). We choose the Martini coarse grained (CG) model as it provides functional-group specificity, and a higher resolution compared to coarser bead-spring polymer models that group entire monomers/Kuhn segments into single CG beads. Using CG molecular dynamics (MD) simulations, we investigate how grafting density, degree of polymerization, and ionic strength affect the conformations of the grafted layer in the presence of explicit water. By simulating both grafted PSS and free PSS, we measure differences in chain conformations and counterion arrangement around the chains to determine which structural changes are induced by surface grafting.