This article describes the tribological properties of well-defined highdensity polymer brushes prepared by the “grafting-from” method based on surface-initiated living radical polymerization. The authors have demonstrated here a water-lubrication system using hydrophilic polymer brushes consisting of 2,3-dihydroxypropyl methacrylate and 2-methacryloyloxyethyl phosphorylcholine (MPC). Macro- and microscopic frictional properties were carried out by a ball-on-plate type tribotester and an AFM cantilever attached with a colloidal sphere, respectively. Friction coefficients and adhesion forces of brush surfaces depend on the solvent quality. For example, the friction coefficient of poly(MPC) brush was reduced to be 0.02 under the highly humid atmosphere because water molecules adsorbed into the brush surfaces acted as a lubricant. Furthermore, high-density polymer brushes showed the low friction coefficient even after 100 reciprocating friction test, which clearly indicates an excellent wear resistance of brush film.
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