Water Adsorption and Friction on Thin Film Magnetic Recording Disks

Abstract

Water adsorption isotherms were measured with two different types of perfluoropolyether lubricants, Zdol 4000 and Ztetraol 2000, on thin film magnetic recording disks. The adsorption isotherm provides the average water film thickness (areal density) as a function of relative humidity. The water film thickness was measured while varying the relative humidity (RH) in the range from dry air to 85%. The water film thickness for both types of lubricants increased with RH, and was independent of temperature between 20° and 50°C. The water film thickness at saturation RH was typically 0.44 nm (16/nm2) for Zdol and 0.25 nm (9/nm2) for Ztetraol. Friction measurements were performed on the same set of disks up to 70% RH. The maximum friction increased with RH, more for Zdol than for Ztetraol, and the friction with Ztetraol was much less than with Zdol. Brief exposure to condensing RH dramatically altered the friction and acoustic emission even at relatively high slider flying height. The altered frictional properties were associated with liquid nanodroplets formed on the disks during the brief condensation.