Scanning force microscopic study of polyethylene single crystals prepared by a self-seeding method

The surface structures of high-density polyethylene (HDPE) single crystals with weight average molecular weight, Mw=32k, 120k and 520k prepared by a self-seeding method were investigated by atomic force microscopy (AFM) and lateral force microscopy (LFM). A characteristic lozenge shape lamellar crystal of ca. 12 nm thick was observed with AFM. The contrast of lateral force of the HDPE single crystal in LFM images was observed between adjacent sectors, which means that the chain folding directions were different. The magnitude of lateral force in LFM measurement increased with scanning angle, θ, which was defined as the angle between scanning direction of the cantilever and {110}, that is the growth face of the HDPE single crystal. These results indicate that the surfaces of the HDPE single crystals prepared by a self-seeding method exhibit regular sharp chain folding along {110} at the surface. Furthermore, it was suggested that the folding structure of the HDPE single crystal surface might depend on the crystallization methods, such as isothermal crystallization or self-seeding one.