Topographical and tribo-chemical studies of contact sliding on ultrathin perfluoropolyether film

Abstract

This paper presents data from topographical and tribo-chemical measurements that were carried out after wear tests on perfluoropolyether (PFPE) films dip-coated on diamond-like-carbon (DLC). The wear experiments were carried out using a glass ball slider sliding on PFPE lubricated (∼2 nm) magnetic hard disks under a normal load of 20 mN and at different sliding speeds. The test conditions were maintained such that only the PFPE film was worn and no wear of either the DLC or the magnetic layer of the disk was observed. After the wear test, the worn PFPE films were analyzed in two ways. The first analysis focused on the changes in the chemical compositions of the film due to sliding operation. The analytical test was carried out using X-ray photoemission spectroscopy. The second analysis observed the topographical changes in the wear zone due to sliding operations. The topography was measured using an ellipsometer. Furthermore, a surface reflectivity analyzer was used to quantitatively compare the features of the worn and unworn zones on the film. From these observations we conclude that contact sliding removes the PFPE film causing some chemical compositional changes which might be related to tribo-chemistry of the surface. On the topography, there is a large roughening of the PFPE film due to sliding. This increased roughness of the film is stable even after leaving the sample for several weeks. Annealed and as-lubricated samples have different effects on the topographical changes.