VELOCITY-DEPENDENT ADHESION WITH LUBRICANTS ON THIN-FILM DISKS

The well-known problem of stiction in a magnetic disk drive largely de pends on the forces induced by the presence of a thin liquid film. It is commonly recognized that both adhesive and viscous effects contribu te to the magnitude of the stiction force, but is is not known what re lative roles the two effects have in a lubricated contact. In the pres ent work, the nature of adhesive and viscous effects is investigated f or the slider/disk interface under conditions of constant-speed slidin g. Friction measurements are conducted over a range of sliding speeds, 0.25-250 mm/s, with eight perfluoropolyether (PFPE) lubricants applie d in various thicknesses, 0-6.6 nm, to carbon-coated magnetic thin-fil m disks. The lubricants were selected to cover a broad range of viscos ities. For several sliding speeds and lubricant film thicknesses, the friction force is found to decrease significantly with increasing slid ing speed for all lubricants. In several instances, large friction for ces are observed at the lowest sliding speeds, indicating stiction-lik e behavior, whereas, at higher speeds, the friction is reduced to even below unlubricated friction levels. At the highest film thickness and sliding speed, the friction was found to increase with speed for some lubricants. The implications of these results on current models of lu bricant-mediated adhesion are discussed.