Effects of Mobile and Chemically Bonded Molecules of Molecularly Thin Lubricant Film on the Vibrational Stability of a Sliding Ball

Lubrication by an extremely thin film has become very important in micro machines, magnetic recording disks and so on. Molecularly thin perfluoropolyether (PFPE) films are considered a good lubricant for these micro devices. When the thickness of the PFPE film is thinned to several nanometers, it is possible to assume that the film consists of mobile and chemically bonded molecules. In this paper, we investigated the role of these molecules from the viewpoint of the vibrational stability of the sliding ball with the disk surface. From experiments by the ball on disk type tribotester, it is found that chemically bonded molecules prevent direct contact between the slider and the disk surface. Furthermore, when mobile molecules exist on bonded molecules, the stability is improved in wide load range.