Abstract
The super hydrophilic polymer brush was prepared by surface-initiated atom transfer radical polymerization (ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC) on the ATRP initiator immobilized silicon wafer. The graft density was estimated to be ca. 0.22 chain/nm2 based on the linear relationship between number average molecular weight, Mn and the thickness in the dried state. The contact angle against water was very low in air and the contact angle of air in water was ca.170 deg. This indicated that the air bubble in water hardly attached on poly(MPC) brush surface, indicating a super hydrophilic characteristics. Neutron reflectivity measurements of poly(MPC) brush showed that the grafting polymer chains fairly extended to the thickness direction from the substrate surface in a good solvent such as water. Shrinking of polymer chain in salt solution was not observed by neutron reflectivity(NR). Frictional properties of the poly(MPC) brushes were characterized by sliding a glass ball probe in air and various solvents at room temperature under the normal load of 0.49 N at a sliding velocity of 90 mm/min. Extremely low friction coefficient of poly(MPC) brush was observed in humid atmosphere because water molecules adsorbed into brush layer acted as a lubricant. The small influence of friction coefficient on ionic strength was observed because of the high graft density and zwitter ionic structure poly(MPC).
