A study of boundary lubrication thin films produced from a perfluoropolyalkylether fluid on M-50 surfaces. II. Humidity effect and topography studies

Tribology experiments under controlled humidity were conducted using a Cameron-Plint tribometer with an M-50 cylinder sliding on an M-50 flat specimen in the presence of a linear perfluoropolyalkylether fluid. The tests were conducted at 100, 70, 59, 10, 7 and 5% relative humidities. The surface thin films formed on the M-50 flat specimen were studied by grazing-angle-microscope! FTIR technique. A thicker surface film of R(f)COOH was observed for the tests conducted at relative humidities equal to or larger than 15%. A monodentate model discussed in the preceding paper was adopted to be the surface film configuration. For the lower humidity tests, an ultra-thin surface film of R(f)COOH-type was observed. An asymmetrical bridging model was proposed to account for this observation. In addition, the nu(asym,OCO) band shifted to lower wave numbers as the relative humidity of the controlled environment was decreased. These band shifts at different humidities warrant the use of the multilayer model over the metal soap model to account for the experimental observation. Topographical and frictional image studies on the cylinder wear scars tested at 100, 98, 70, 59, 15 and 5% relative humidities have been carried out using atomic force and frictional force microscopies. Residual surface features were found to be present on those specimens tested at 100, 98, 70, 59 and 15% relative humidities. These findings are complementary with the results obtained from the M-50 flat specimens studied by GAM/FTIR technique.