AFM studies on microtribology of concentrated polymer brushes in solvents

Abstract

In concentrated polymer brushes (CPBs) prepared by surface-initiated living radical polymerization, graft chains in a good solvent are highly stretched, nearly to their full length, giving properties quite different and unpredictable from those of semi-dilute polymer brushes (SDPBs) previously studied. This paper reviews our recent studies on the microtribology of confronted CPBs in solvents. Atomic force microscopy revealed that the CPBs of poly(methyl methacrylate) and poly(styrene) showed dramatically low frictional coefficients in good solvents compared with those of the corresponding SDPBs. This was reasonably ascribed to confronted CPBs hardly mixing with each other due to their huge osmotic and elastic interactions. The lubrication mechanism of CPBs was discussed according to the sliding-speed dependency of frictional coefficient, and two different mechanisms, boundary and hydrodynamic lubrications, were suggested. Thermo-responsive lubrication was also demonstrated for the CPB of poly(N-isopropyl acrylamide). We believe that these studies will open up a new route to precision surface modification for "super" lubrication.