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No.2（2007）14.Effect of heat treatment on chemisorption behavior of PFPE on DLC film surface
Masahiro Kawaguchi, Saiko Aoki, Atsushi Mitsuo
Diamond-Like Carbon (DLC) film, which is a new coating technique, has been applied to various material surfaces such as metals, plastics, glasses and rubbers. For example in industries, scrubbed parts surface of automobiles, cutting tools, disk surface of hard disk drives and so on are coated with DLC film. DLC film has been extensively investigated by both experimental and theoretical methods in order to clarify its friction and wear properties. In sliding tests under lubricated conditions, chemisorptions of lubricant molecules on DLC surface are very important because chemisorptions are one of the factors which dominate the tribological behaviors at a sliding interface. However, chemisorptions of lubricant molecules on DLC surface are not well known because the reaction mechanism is dependent on many factors such as procedure of DLC deposition, kinds of lubricant and test conditions. On the other hand, it is reported that the amount of chemisorptions of perfluoropolyether (PFPE) lubricated on DLC surface increases with the increase in the heat treatment time. This experimental result is very interesting, however, the details of this reaction are not well known. In this study, we focus on the reaction mechanism between PFPE molecules and DLC surface. PFPE molecules are applied to DLC surface by dip-coating method and vacuum vapor deposition method. The amount of PFPE chemisorptions is evaluated by XPS measurements. In addition, a simple reaction model based on the chemical kinetics is developed and the expression is derived. The experimental and calculated results are compared with each other. As a result, we conclude firstly that the reaction will be roughly dominated by the formation of covalent bonds and hydrogen bonding between DLC surface and PFPE molecules. Secondary the incorporation of nitrogen atoms into DLC film is effective for the increase in the amount of PFPE chemisorptions due to the hydrogen bonding between the end group of PFPE and the amine on DLC surface. Finally the reaction model we have proposed can express the experimental results well.
Keywords
diamond-like carbon (DLC) film, perfluoropolyether (PFPE), chemisorptions, Arrhenius equation
