Molecular Conformation at the Crystal Amorphous Interface in Polyethylene

Torsional-tapping AFM with supersharp carbon-whisker tips is used to explore the molecular conformations at the surface of a semicrystalline polymer. Images of the crystal amorphous interface of oriented polyethylene have allowed us to measure hitherto inaccessible parameters that can be directly compared to polymer crystallization theories and molecular simulations, such as the length of stem-to-stem overhang. It has also been possible to identify both first- and second-neighbor folds and to determine the surface roughness of lamellae which we find approximately doubles the interfacial area. Finally, we calculate the interfacial density profile from the images and find it to be sigmoidal but narrower than values reported by SAXS measurements.