Scanning force microscopic study of surface structure of polyethylene single crystals

The surface structure of high-density polyethylene (HDPE) single crystals prepared by the self-seeding method was investigated by atomic force microscopy (AFM) and lateral force microscopy (LFM). Characteristic lozenge-shaped lamellar crystals of ca. 5 μm long and ca. 12 nm thick were observed with AFM. The contrast of the lateral force between neighboring sectors of the HDPE single crystal surface could be detected when the scanning direction was different between neighboring sectors. The magnitude of the lateral force increased with an increase of the scanning angle, θ, with respect to the (110) plane. These results indicate that the surfaces of the HDPE single crystals with M_w=23k, 32k, 93k, 120k, and 520k prepared by the self-seeding method was composed of regular sharp chain-folds. It has been reported that the folding structure of the HDPE single crystal surface with M_w=520k prepared sporadically by a conventional isothermal crystallization method was switchboard-like structure. These results apparently indicate that the folding structure of the HDPE single crystal surface depends on the crystallization process or method.