Effect of adsorbed water on perfluoropolyether-lubricated magnetic recording disks

Abstract

The impact of water on the hydroxyl-terminated perfluoropolyether, Zdol, and the amorphous carbon overcoats commonly used on magnetic recording disks was investigated via computer modeling, kinetic experiments, and surface energy measurements. Water is shown to interact via hydrogen bonding with the hydroxyl end groups of Zdol and the polar, carbon–oxygen functionalities on the carbon overcoat. The interaction between water and the hydrophobic perfluorinated backbone is, however, repulsive. The corrosion susceptibility of Zdol lubricated magnetic recording disks was also studied. Reduced levels of corrosion were observed when the total Zdol thickness, and/or the bonded thickness, were increased. The results are consistent with a heterogeneous corrosion mechanism in which electron transfer from the polar functionalities on the carbon overcoat to the surface adsorbed water is the rate limiting step. The disk lubricant inhibits the electrochemical conductivity of the disk surface by; (a) a screening of the electrochemically active surface sites by the hydrophobic perfluoropolyether backbone, and (b) a neutralization of the surface active sites by hydrogen bonding of the hydroxyl end groups of Zdol.