Scanning force microscopy of the crystalline/amorphous interface of ultradrawn poly(ethylene)

Abstract

We report on high-resolution experiments by Scanning Force Microscopy (SFM) indicating the tight folding of neighbouring molecular chains in Poly(Ethylene) (PE) crystals. Ultradrawn PE films were prepared in the stacked lamellar morphology exhibiting crystalline lamellae and amorphous parts. The [001] direction of the lamellae is aligned parallel to the substrate surface resulting in {hk0} planes perpendicular to the symmetry axis of the probing tip. This preparation technique allows the direct observation of the molecular arrangement in polymeric crystals as well as an investigation of the crystalline/amorphous interface by SFM: at lower magnification, crystalline and amorphous parts of the film can be distinguished clearly. High-resolution imaging on the crystalline lamellae reveals a PE pitch height of 0.26±0.02 nm while the interchain spacing measures 0.50±0.02 nm consistent with (100) lattice planes aligned parallel to the substrate surface. Finally, the molecular folding at the edges of the lamellae has been studied. Evidence is found for the adjacent reentry of individual molecules at the edge of (100) surfaces.