Tribology of shearing polymer surfaces. 2. Polymer (PnBMA) sliding on mica

Quantitative friction force measurements were made using a Surface Forces a pparatus (SFA) modified for friction studies of a smooth poly(n-butyl metha crylate) (PnBMA) surface sliding on a stationary mica surface, and the resu lts are compared with those of the complementary system (ref 1) of mica sli ding on a stationary polymer surface. The results indicate that qualitative ly and quantitatively different tribological behavior may be expected-as ma nifested by smooth or stick-slip sliding, high or low steady-state friction stresses, transient effects such as stiction, and surface deformations and wear-for such "asymmetric" surfaces depending on whether the sliding or st ationary surface carries the lubricant or polymer layer, on whether the mot ion is continuous in one direction or cyclic (back and forth), and on the a rea of the contacting junctions. None of these effects would arise if the f riction forces were determined solely by the instantaneous load (pressure) and velocity (shear rate) of the shearing junctions, which is generally ass umed in conventional theories or models of friction.