This chapter describes the tribological properties of well-defined high-density polymer brushes prepared by the “grafting-from” methods based on surface-initiated controlled radical polymerization. The authors have demonstrated the enhanced lubrication and wear resistance of high-density polymer brushes, and the superior tribological properties in the good solvent. Macro- and microscopic frictional properties were examined by a ball-on-plate type tribotester and an AFM with a colloidal sphere-tip cantilever, respectively. Friction coefficients and adhesion forces of polymer brush surfaces depend on the compatibility to the solvents. The friction coefficient of charged polymer brushes was reduced to less than 0.1 under highly humid atmosphere, whereas the hydrophobic brushes represented friction coefficient reduction under hydrocarbon solvents. The high-density polymer brushes kept the low friction coefficient even over 100 reciprocating friction cycles, indicating the excellent wear resistance. The lubrication mechanism in good solvents was investigated by ultra-thin-film interferometry study. The gap between rotating disc and loading sphere showed significant increase with increasing sliding velocity, indicating that the charged polymer brushes promoted the formation of hydrodynamic fluid lubrication layer.
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