(252f) Correlation of Polymeric Surfactant Film Surface Characteristics to Nanotribological Performance

Surface active low molecular weight poly(isobutylene) additives function as friction modifiers and dispersants in lubrication applications. In automatic transmissions, they are used to reduce stick-slip (shudder) by enhancing the dynamic coefficient of friction. AFM-based nanotribological tests have been devised to determine the origin of this behavior through the deposition of thin films on silicon wafers. The friction of the thin films exhibit varying degrees of load and speed dependence depending on film thickness. With thicker films, the friction increases with speed regardless of load, as seen in macroscale tribological tests. With thin films, the speed dependence shifts from increasing with speed to decreasing with speed as load is increased. Surface analysis using low energy ion spectroscopy and sum frequency generation are used to correlate surface morphology and density with frictional behavior.