ANISOTROPIC FRICTION AT THE SURFACE OF LAMELLAR CRYSTALS OF POLY(OXYMETHYLENE) BY LATERAL FORCE MICROSCOPY

Lamellar crystals of poly(oxymethylene), POM, grown from dilute solutions in bromobenzene, were studied in simultaneous contact mode atomic force microscopy, AFM, and lateral force microscopy, LFM, experiments. AFM scans showed the expected hexagonal crystal habit with clearly resolved chain fold domains at the surface of the lamellae defined by the diagonals and the edges of the crystals. The frictional force within the domains, obtained in LFM experiments, was found to depend on the relative scan direction. This result is explained by the presence of molecular loops arising from chain folds at the folded surface, which are oriented predominantly parallel with the edges of the crystals in the different chain fold domains.