ABSTRACT
Frictional properties of organosilane monolayers and high-density polymer brushes on silicon wafer were investigated by lateral force microscopy (LFM) and ball-ondisk type tribotester. The ultrathin lms of alkylsilane and uoroalkylsilane monolayers with a series of chain lengths (C8-C18) were prepared by the chemical vapor adsorption method. LFM nanoscale measurements of tribological properties showed that the lateral force of alkylsilane monolayer decreased as the length of the alkyl chain increased. The macroscopic frictional properties were characterized by sliding a stainless steel ball (φ10 mm) probe on its surface across a width of 20 mm at a rate of 90 mm/min under a load of 0.49 N in air at room temperature. The monolayer with longer alkyl chain and bilayer of organosilanes revealed excellent wear resistance. The microscopically line-patterned two-component organosilane monolayers were also fabricated and their macroscopic friction behavior was investigated. Even though the height difference between the two components was less than 1 nm, friction force anisotropy between the parallel and perpendicular directions against the line pattern was observed. Polymer brushes with high graft density were prepared by surface-initiated atom transfer radical polymerization of methyl methacrylate (MMA), (2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate (DMM), and 2-methacryloyloxyethyl phosphorylcholine (MPC) from silicon wafer immobilized with a 2-bromoisobutylate moiety. Poly(DMM) brush was further converted to the hydrophilic polymer brush consisting of 2,3-dihydroxypropyl methacrylate (DHMA) units, successively. Frictional properties of the polymer brushes were characterized by sliding a glass ball probe in air and various solvents under a normal load of 100 MPa. The PMMA brush was found to have a lower friction coefcient and much better wear resistance than the corresponding spin-coated PMMA lm because of the strong anchoring of the chain ends in the brush. In addition, the friction coefcient of the polymer brush signicantly decreased in response to soaking in toluene, and increased in response to immersion in cyclohexane. The hydrophilic poly(DHMA)
and poly(MPC) brushes showed low dynamic friction coefcient in water. These results indicated the dependence of the tribological properties on the solvent.
