Nanofriction on Sodium Polystyrene Sulfonate Brushes in Water
  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. 
Takuya Fujima, Eitaro Futakuchi and Fumihiro Kino
cond-mat.soft