Adhesion and friction properties of polymer brushes: Fluoro versus nonfluoro polymer brushes at varying thickness

A series of different thicknesses of fluoro poly(2,2,2-trifluoroethyl methacrylate) and its analogous nonfluoro poly(ethyl methacrylate) polymer brushes were prepared via surface-initiated ATRP (SI-ATRP) on Si(111) surfaces. The thiol-yne click reaction was used to immobilize the SI-ATRP initiator with a high surface coverage, in order to achieve denser polymer brushes (grafting density from ~0.1 to 0.8 chains/nm2). All polymer brushes were characterized by static water contact angle measurements, infrared absorption reflection spectroscopy, and X-ray photoelectron spectroscopy. Adhesion and friction force measurements were conducted with silica colloidal probe atomic force microscopy (CP-AFM) under ambient and dry (argon) conditions. The fluoro poly(2,2,2-trifluoroethyl methacrylate) polymer showed a decrease in adhesion and friction with increasing thickness. The analogous nonfluoro poly(ethyl methacrylate) polymer brushes showed high adhesion and friction under ambient conditions. Friction coefficients down to 0.0057 (ambient conditions) and 0.0031 (dry argon) were obtained for poly(2,2,2-trifluoroethyl methacrylate) polymer brushes with 140 nm thickness, which are the lowest among these types of polymer brushes