HREELS, XPS and in-situ friction studies of thin polyphenyl ether films on steel surfaces

Abstract

The surface chemistry of thin films of polyphenyl ether (5P-4E) lubricant on clean and oxidized M-50 steel surfaces were studied using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS) coupled with in-situ friction measurements. Polyphenyl ether films were applied in-situ by evaporation. Liquid film thicknesses were obtained using both XPS and ellipsometry. HREELS and XPS of evaporated films of 5P-4E onto both clean and oxidized M-50 steel surfaces indicate reaction of the lubricant with the substrate occurs at room temperature. XPS results suggest C-O bond cleavage occurs producing metal oxide. HREELS results suggest loss of aromatic character of the adsorbed 5P-4E occurs as well. Friction measurements for varying 5P-4E film thicknesses show that ∼ 100 Å films are needed to drop the friction from 2.0 (clean surface value) to 0.3 XPS studies of scratched areas show changes due to reaction which are similar to those measured in the thermal reactions. Wetting of surfaces by 5P-4E was found to be a strong function of surface cleanliness. XPS and ellipsometry show that the degree of film continuity depends upon the amount and/or nature of carbon on the surface. The implications of these results to lubrication are discussed.