Lifshitz-van der Waals and Lewis Acid-Base Approach for Analyzing Surface Energy of Molecularly Thin Lubricant Films

The dispersive and polar components of surface energy, which are typically obtained from the two-liquid geometric method through contact angle measurement, have been extensively used to study the interfacial properties of perfluoropolyether (PFPE) lubricated media used in hard disk drive industry. In this paper, an alternative approach, Lifshitz-van der Waals and Lewis acid-base (LW/AB) theory, which provides additional information on the nature of lubricant/overcoat interaction, has been applied to the study of the surface energy of PFPE-coated media. Here, the surface energy is decomposed into Lifshitz-van der Waals (LW), Lewis acid, and Lewis base components. The results of Lewis acid and Lewis base components of surface energy suggest that the bonding of functional PFPEs with a carbon overcoat is a Lewis acid-base interaction; the overcoat is an electron donor and functional PFPEs are electron acceptors. It was also found that the LW surface energy has a sequence of Ztetraol<Zdol<AM2001<A20H<Z03 for films with the same thickness, which is in the reverse sequence as found in the bonded thickness of these PFPEs. A molecular-level bonding mechanism is proposed to explain the experimental results