Grazing Incidence X-ray Diffraction Study on Surface Crystal Structure of Polyethylene Thin Films

Crystal structure in thin films of melt-crystallized and annealed polyethylene (PE) was examined by grazing incidence X-ray diffraction measurements. Choosing appropriate incident angles of X-rays to the films, surface and bulk molecular aggregation states were successfully extracted. Consequently, it was found that chain packing structure in the surface region was different from that in the bulk one. Based on paracrystalline analysis for the (110) reflection and its higher-order ones of PE orthorhombic crystal, it was clarified that the ordering for the crystalline lattice was lower in the surface region. Also, apparent crystallinity in the surface was lower than the bulk one. These results indicate that disordered crystallites were preferentially formed in the surface region.