CHAIN MOBILITY AND PULL-OUT EFFECTS IN LUBRICATION AND FRICTION

The interfacial shear stress that occurs when a network of a polymer that is highly mobile at the segment level (an elastomer) is slid over the smooth surface of an immobile (glassy) polymer has been measured. The glassy material is covered by a thin layer of end-attached chains of the mobile material. The experiment was designed so that there were no free chains at the interface; the slip occurred between network chains on the one side and rigid material plus end-attached mobile chains on the other. Two main results were obtained: (1) The interfacial shear stress was found to be strongly affected by the mobility of the materials on both sides of the slip plane, considerably lower stress was observed when both sides of the interface were highly mobile. (2) Very thin layers of tethered chains were found to increase the interfacial friction.