The Tribological Properties of a New Cyclotriphosphazene-Terminated Perfluoropolyether Lubricant

We have investigated the tribological properties of a novel perfluoropolyether (PFPE) lubricant truncated on one end by a hydroxyl group and on the other end by a cyclotriphosphazene derivative. A measurement of the friction force as a function of molecular weight indicates that the dynamic clearance between the slider and the disk can be reduced by ∼1.5 nm by decreasing the molecular weight from 5300 to 2400 g/mol. However, the thermodynamic film stability of the novel PFPE lubricants, as determined by surface energy measurements and ellipsometric imaging of lubricant dewetting, becomes increasingly unstable at lower film thicknesses with decreasing molecular weight. Measurements conducted on lubricant mobility indicate that the novel PFPE lubricants are relatively immobile compared to the Zdol perfluoropolyether lubricants and hence resist film thinning to a greater degree. These data provide the direction for the optimization of the molecular weight of these novel PFPE lubricants.