Solvent Effects on Friction Properties of Monolayer Perfluoropolyether Films Coated on Magnetic Disk Surfaces

Monolayer perfluoropolyether (PFPE) films used for lubrication of magnetic disks are generally dip-coated from the PFPE solutions diluted by fluorinated solvents. In this paper, under lightly loaded (0-1 mN) and slowly rotated (2.1 mm/s) conditions that suppress disturbance of PFPE films during sliding, we investigate the effect of solvents on the friction properties of monolayer PFPE films coated on magnetic disk surfaces. The solvents include HFE-7200 and Vertrel-XF. For polar Zdol2000 and Zdol4000 films, friction fluctuated during one revolution of the disk immediately after film deposition, but became stable with elapsed time. Such transient friction behavior was not observed for nonpolar Z03 films, suggesting that the friction fluctuations exhibited by Zdol2000 and Zdol4000 films result from PFPE microstructure (such as film uniformity and molecular conformation) induced by the polar end groups. Despite of the higher solvent power of Vertrel-XF, the friction fluctuations in the transient state were noticeable for the films applied with Vertrel-XF as compared with those applied with HFE-7200. However, because the friction fluctuations were characterized by intermittent decrease of friction in narrow and sparsely distributed regions, the average value of the friction measured during one revolution of the disk was almost not affected by the friction fluctuations and showed weak dependence on the solvent.