MOLECULAR FOLDS IN POLYETHYLENE OBSERVED BY ATOMIC-FORCE MICROSCOPY

Folded chain lamellar crystals of polyethylene were examined by atomic force microscopy. Particular care was taken to ensure that the areas examined at high magnification were on the fold-containing surface of the crystals. High spots observed on this surface formed a 2D array. The spacings and angles of the array were consistent with the positions expected for the folds when viewed from a direction perpendicular to the fold-containing surface and were not the same as expected if viewed along the chain axis. Spacings appropriate for the usual orthorhombic unit cell and for the monoclinic unit cell that can be produced by mechanical deformation were observed. Local variations in the shape and position of the spots indicate that folds of different orientation and structure were present. In many observations of similar fold surfaces at high magnification, only images of lower quality which did not show the periodic arrays of spots were observed. Reasons for the images without periodic order are proposed.