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

The spreading of OH-terminated perfluoropolyalkylether (PFPE), Zdol, on amorphous carbon surfaces was studied as a function of hydrogen or nitrogen content in the carbon film, using scanning micro-ellipsometry. A layered structure of the thickness profiles was observed, which remained qualitatively the same for all carbon types. The sharpness of the second layer was gradually eroded as either hydrogen or nitrogen content in the films was increased. The thickness-dependent diffusion coefficient was calculated using the Matano interface method. It was observed that the surface mobility of Zdol increased as hydrogen content increased, but decreased as nitrogen content increased. Implications of these results on the boundary lubrication properties of Zdol on carbon films are discussed.