Anisotropic Stick-slip friction of highly oriented thin films of poly(tetrafluoroethylene) at the molecular level

Lateral force microscopy (LFM) studies of poly(tetrafluoroethylene) (PTFE) films with molecular resolution are reported. Thin PTFE layers with a high degree of orientation were obtained by pressing and sliding a block of polymer on a clean, heated muscovite mica substrate. LFM nanographs obtained on these films by scanning at directions between ca. 40 and 90° with respect to the film orientation direction, i.e. with respect to the direction of the polymer chains, showed a “stick-slip” type frictional motion of the LFM probe tip at the molecular level. The friction force observed at constant load decreased with decreasing scan angles. Chain-chain packing distances obtained by LFM and contact…