Spatial inhomogeneity of chain orientation associated with strain-induced density fluctuations in polyethylene

We found the spatial inhomogeneity of chain orientation on the submicron scale in polyethylene (PE) under strain by scanning transmission X-ray microscopy (STXM). Our previous study [1] clarified that straininduced density fluctuations on the submicron scale and that density fluctuations strongly affected the mechanical behavior of PE during strain. Strain is expected to induce the spatial inhomogeneity of chain orientation as well as density fluctuations, and the spatial inhomogeneity might also affect the mechanical behavior. However, wide-angle X-ray scattering can be used to explore the spatially averaged local structure, and the spatial inhomogeneity of chain orientation on the submicron scale has not yet been investigated. To clarify the spatial inhomogeneity of chain orientation, we observed near-edge X-ray absorption fine structure (NEXAFS) spectra at the carbon K-edge of stretched PE, with a resolution on the order of 10 nm, by STXM and investigated the spatial inhomogeneity of chain orientation as well as density fluctuations. The intensity of the NEXAFS spectra revealed that the chains were more oriented in the low-density region under stretching. The orientation was induced by the stretching of the polymer chains mechanically melted.