Wing T. Tang

Degradation of perfluoropolyethers Catalyzed by Aluminum Oxide

Thermal stabilities of perfluoropolyethers, Fomblin Z, Fomblin Y, Krytox, and Demnum in the presence of Al2O3 were examined. Fomblin Z was found to degrade at 200°C in two stages, the slow first stage, and the vigorous second stage leading to complete loss of fluid. It is concluded that oxide-to-halide conversion occurs on Al2O3 surface during the first stage. The second stage is attributed to a catalytic process induced by Lewis acid AlF3. Based on NMR and mass spectroscopic evidences the following reaction mechanism is advanced for the second stage: (1) a bidentate linkage is formed between an acidic aluminum and two oxygen atoms of an acetal unit (-O-CF2-O-) of Fomblin Z chains, and (2) the partial positive charge thus developed at the acetal carbon induces a fluorine atom transfer from the adjacent CF2 unit onto the acetal carbon and results in chain scission with transformation of the acetal sector into a methoxy end-group (-O-CF3) and the adjacent unit into either an acylfluoride end-group (FCO-CF2-), or a fluoroformate end-group (FCO-O-CF2-). Lacking acetal units Krytox and Demnum are stable against this degradation process. In the case of Fomblin Y, owing to the paucity of acetal units, no reaction was observed when heated in the presence of Al2O3; when heated with AlCl3, removal of acetal units and consequential formation of functional end-groups were observed.

The dependence of stiction and friction on roughness in thin‐film magnetic recording disks

The influence of surface roughness in determining the tribological behavior of carbon coated thin‐film magnetic recording disks have been investigated. Contact start/stop and low‐speed drag tests were performed on unlubricated disks as well as disks that were coated with different thickness of a perfluoropolyether lubricant. Measurements of stiction and friction were made on disks with different surface roughness and using Al2O3–TiC sliders. Experimental results show that both stiction and friction are reasonably independent of the surface roughness above a certain value but show a sharp increase for tests on the smoother disks. The experimental findings are explained on the basis of currently accepted models for stiction that considers surface tension and viscous properties of the surfaces and possible effects arising from contamination.

End Group Effects on Adhesion of Perfluoropolyether Lubricants to Solid Substrates

Abstract Interfacial interactions of several commercial perfluoropolyether (PFPE) and aromaticmodified lubricants with silicon oxide or carbon substrates were investigated through contact angle measurement, dipping tests, fluorescence spectroscopy and contact-start-stop testing. All commercial lubricants that have not been thermally treated are displaced from the solid substrate by contact with water. Contact angles of water on ZDOL, a PFPE doubly-terminated with hydroxyl groups, spun on silicon and carboncoated wafers were measured as a function of thermal annealing treatment. The adhesion of commercial lubricants to such previously thermally-bonded layers is stronger than to the bare silicon wafers. The thermal reaction of ZDOL on silica gel and carbon was investigated by thermogravimetric analysis and FTIR. The thermal reaction takes place when the baking temperature exceeds 70°C; at least part of this surface-bonding involves condensation of terminal hydroxyl groups with isolated surface silanols. Fin...