Nanofriction on Sodium Polystyrene Sulfonate Brushes in Water

Abstract: We investigated the frictional properties of sodium polystyrene sulfonate (NaPSS) brushes in water by frictional force microscopy (FFM). Polyelectrolyte brushes were prepared on silicon wafers by the grafting-to method. The brushes considerably reduce the frictional force and coefficient of kinetic friction compared to hydrodynamic lubrication on a smooth Si wafer. Frictional force is independent of sliding speed, but is lower for lower degrees of NaPSS polymerization. Nanoindentation tests indicate that the polymer chains in a brush are stretched strongly away from the substrate. These results suggest that polymer chains point support the FFM probe tip in water and reduced contact area and friction.