Spreading of PFPE lubricants on carbon surfaces: effect of hydrogen and nitrogen content

The spreading of OH-terminated perfluoropolyalkylether (PFPE), Zdol, on amo rphous carbon surfaces was studied as a function of hydrogen or nitrogen co ntent in the carbon film, using scanning micro-ellipsometry. A layered stru cture of the thickness profiles was observed, which remained qualitatively the same for all carbon types. The sharpness of the second layer was gradua lly eroded as either hydrogen or nitrogen content in the films was increase d. The thickness-dependent diffusion coefficient was calculated using the M atano interface method. It was observed that the surface mobility of Zdol i ncreased as hydrogen content increased, but decreased as nitrogen content i ncreased. Implications of these results on the boundary lubrication propert ies of Zdol on carbon films are discussed.