Scanning probe microscopy nanotribological experiments on thick polystyrene films have been performed that support the hypothesis that crazing is the mechanism of ‘bundle’ formation. In these fatigue studies, surface patterning appears abruptly at a critical friction, and can either occur spontaneously or be triggered by surface imperfections. After pattern initiation, progressive scanning smoothly increases surface roughness. Friction histograms of these in situ patterned surfaces reveal two distinct friction regions that are statistically correlated with the topography. Using a topography-friction cross-correlation function, high friction was found to coincide with topographic troughs. This supports crazing as the mechanism of deformation, in which surface fracture at troughs leads to fibril formation, consistent with the observation of higher energy dissipation.

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