Tribological performances of the oils containing polylaurylacrylates with and without hydroxyethyl group were studied under elastohydrodynamic lubrication (EHL), partial EHL and the boundary lubrication conditions. The base oil was polyalphaolefin and the viscosity of polymer solutions and the concentration of polymer was adjusted at the same level. Under the partial elastohydrodynamic contacts using a ball-on-disk type tribometer, polylaurylacrylatehydroxyethylacrylate (PLA/HEA) showed a greater oil film thickness while lower traction coefficient at low rolling speeds than polylaurylacrylate (PLA). This can be interpreted that adsorption of hydroxyethyl group of PLA/HEA reduced traction under the partial EHL condition. Under the boundary lubrication conditions using a pin-on-disk type tribometer, PLA/HEA exhibited the flat friction-velocity relation while PLA showed a large negative gradient of friction-velocity relation. Finally, PLA/HEA was superior to PLA in terms of the antiwear properties with a reciprocating friction tester. It is inferred that these better performances of PLA/HEA under the boundary lubrication conditions were brought about by formation of a tribofilm based on reaction of hydroxyethyl group and the sliding surface.
The adsorption behavior and lubrication behavior of oleic acid on Si3N4 in ethanol and in hydrocarbons were investigated. The adsorption behavior was evaluated by contact angle measurement and by thin layer chromatography. The results suggested that oleic acid was adsorbed by Si3N4 both in ethanol solution of oleic acid and in n-undecane solution of oleic acid. The results also suggested that the adsorbed oleic acid was eluted from the oxidized surface of Si3N4 more easily with ethanol than with n-hexane. The lubrication behavior was examined by using a pin-on-disk machine. Si3N4 disk was slid against Si3N4 pin in ethanol, in n-undecane, in ethanol solution of oleic acid and in n-undecane solution of oleic acid. The addition of oleic acid resulted in decrease in friction and wear of Si3N4 both in ethanol and in n-undecane. In ethanol solution of oleic acid, ethoxysilane gel, which was tribochemical reaction product, and adsorbed oleic acid seemed to act as boundary lubrication film. In n-undecane solution of oleic acid, adsorbed oleic acid and friction polymer seemed to act as boundary lubrication film.