Interfacial interactions of perfluoropolyether lubricants with magnetic recording media

Perfluoropolyethers (PFPE) are low surface tension liquids that are commonly employed in magnetic recording devices (hard-disk drives) as disk lubricants. In current drives, a single monolayer (or less) of a PFPE is applied to the amorphous carbon overcoat of the hard disk to provide the necessary lubrication of the head-disk-interface. The focus of the current paper is to demonstrate the utility of surface energy measurements in extracting information on the PFPE lubricant-carbon interfacial interactions. In particular, surface energies are reported as a function of applied lubricant thickness in the range of 2-30 Å for three Fomblin Z lubricants, i.e., ZDOL, ZDIAC, Z-15; and two Demnum lubricants, i.e. Demnum SA and SP. We show that from the surface energy measurements one can: (a) determine the extent of lubricant coverage of the carbon surface, (b) determine the orientation of the lubricant with respect to the carbon surface, (c) determine the nature of the lubricant-carbon interaction, e.g. attractive vs. repulsive, and (d) obtain an estimate of the interaction strength between the lubricant and the carbon.