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

The macrotribological behavior observed when a Si3N4 ball of a friction tester slid on polystyrene (PS) surface was compared with the nanotribological behavior observed when a Si3N4 tip of a scanning force microscope (SFM) slid 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 observations. Surface plastic deformation of PS always occurred under both tribological conditions examined in this study. The morphology formations of the macrocrack and the nanoperiodic pattern that might be attributed to the crack opening were observed at the rubbed PS surfaces under the macro- and nanotribological 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 contact pressure, these surface plastic deformations yielded similar values of the macro- and nanofriction coefficients. The friction coefficient was considerably influenced by surface plastic deformation regardless of measurement scales. These results demonstrated that the macro- and nanotribological mechanisms of PS were similar.