Water Lubrication System Supported by High-density Hydrophilic Polymer Brush

Surface-initiated atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) was carried out to produce high-density poly(MPC) brush on silicon wafer. Frictional properties of poly(MPC) was investigated by by sliding a glass ball (${\phi}\;10\;nm$) on the substrates over a distance of 20 mm at a sliding velocity of 90 mm/min under loading of 0.49 N at 298 K. Higher friction coefficients were observed in dry N2 atmosphere and in toluene condition, whereas the friction coefficients decreased to 0.02 in humid air and in water. It is supposed that water-swollen poly(MPC) brush works as a lubricant to moderate the interaction between brush and probe.