Electric contact resistance between finely polished nickel plates with PFPE coating and its relation to friction

The electric contact resistance between mechanically polished nickel plates, with one side dip-coated in perfluoropolyether (PFPE), was evaluated under statically loaded and sliding conditions to investigate the isolation property of the PFPE coating, which may have an important role in thin-film lubrication on relatively large, minutely rough, plane surfaces. The nickel plate surfaces had a roughness of 1–3 nm and the PFPE coating had a thickness of 4–6 nm. Two types of relationship between load and contact resistance were observed. One was estimated to be for a uniform coating of the oil film, the other for a patchy one. Friction tests revealed that a uniform coating of oil film would be preferable to a patchy one to prevent solid–solid contact, if the nominal thicknesses of the oil films were similar.