Degradation off perfluoropoly(ethers) and role of X-1P additives in disk files

Abstract

Perfluoropoly(ethers) (PFPE's) are the current lubricant of choice for magnetic recording media. It is shown that the degradation of PFPE's in the disk environment is singularly dominated by the intramolecular disproportionation reaction of the following scheme: R-CF2-O-CF2R→R-CF3+F-C∥O-R The reaction is catalyzed by Lewis acid sites (e.g., Al2O3 or AlCl3) and occurs at sectors where the successive ether oxygens have an odd number of backbone carbons between them. When the number of such backbone carbons is even throughout the chain, the reaction occurs exclusively at chain ends. The degradation of PFPE's Fomblin Z, Fomblin Y, Krytox, and Demnum is briefly recounted. A fundamental difference at the molecular level between the two types of degradation (for the odd vs. even number of carbons) leads to profound differences in macroscopic manifestations in test tubes as well as in disk files. Examples of such manifestations are shown and discussed. X-1P (partially fluorinated hexaphenoxy cyclotriphosphazene) is topically advocated as an additive to PFPE in disk applications. Its efficacy has been attributed to its ability to cover the catalytically active slider material (Al2O3/TiG). A spectroscopic study (NMR, ESR) of X-1P revealed a strong nucleophilic (Lewis base) nature of the triphosphazene ring. A plausible adsorption and reaction mechanism based on the spectroscopic and molecular model studies is presented.