Comparison of macro- and nanotribological behavior with surface plastic deformation of polystyrene

The macrotribological behavior observed when a Si3N4 ball of a friction tes ter slid on polystyrene (PS) surface was compared with the nanotribological behavior observed when a Si3N4 tip of a scanning force microscope (SFM) sl id on the same surface. The macro- and nanofriction forces were measured by a conventional ball-on-disk type friction tester and a SFM, respectively, as a function of the applied load. The morphological changes of the rubbed PS surfaces were also characterized by optical microscopy or SFM observatio ns. Surface plastic deformation of PS always occurred under both tribologic al conditions examined in this study. The morphology formations of the macr ocrack and the nanoperiodic pattern that might be attributed to the crack o pening were observed at the rubbed PS surfaces under the macro- and nanotri bological conditions. It should be noted that these formations occurred at the same level of apparent average contact pressure estimated based on the Johnson-Kendall-Roberts contact theory. Furthermore, under a comparable con tact pressure, these surface plastic deformations yielded similar values of the macro- and nanofriction coefficients. The friction coefficient was con siderably influenced by surface plastic deformation regardless of measureme nt scales. These results demonstrated that the macro- and nanotribological mechanisms of PS were similar.