The interactions between Z-Tetraol perfluoropolyether lubricant and amorphous nitrogenated- and hydrogenated-carbon surfaces and silicon nitride

The interactions that occur between the hydroxyl-terminated perfluoropolyether Z-Tetraol and the ion beam-deposited amorphous hydrogenated CHx, sputtered amorphous nitrogenated carbon CNx, and sputtered amorphous silicon nitride SiNx surfaces, are investigated via surface energy measurements, kinetic measurements, and ab initio calculations. The film thickness dependence of the Z-Tetraol dispersive surface energy can be fit using a repulsive van der Waals potential, where the repulsion between the Z-Tetraol main chain and the underlying surface increases in the order: CHx (IBC) < CNx < SiNx, due to the increased average separation between the lubricant main chain and the underlying surface. Ab initio calculations on model dimers quantify the separation distances and binding energy of the lubricant/surface interactions. The Z-Tetraol thickness dependence of the polar surface energy indicates that strong polar interactions occur between the applied lubricant and the underlying surface. The decrease in the polar surface energy is correlated to the increased level of bonding between the hydroxyl end groups of Z-Tetraol and the polar sites of the underlying surface. Further analysis of the surface energy data identifies the critical film thickness at which film instability occurs to be near 17.5±1.0 Å for the 2200 molecular weight of Z-Tetraol on the various surfaces. Images of the disk surfaces showing the evolution of lubricant droplets due to dewetting corroborate the surface energy data analysis.