Effects of Mobile and 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 micromachines, 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 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 both mobile and bonded molecules exist on the disk surface, the bouncing vibration of the sliding ball can be reduced wide load range. In the case where only mobile or only bonded molecules exists, there is little effect on the bouncing vibration.