Presentation Structural Evolution in Deformed Polyethylene Studied with Positrons

Y.Kobayashi  ,  Yamawaki, M.  ,  Oka, T.  ,  Sato, K.  ,  Uesugi, N.  ,  Hattori, K.  ,  Nagasawa, N.  ,  Washio, M.

Different kinds of polyethylene were subjected to uniaxial deformation and their structural evolution was investigated by positron annihilation lifetime spectroscopy (PALS) and coincident Doppler broadening spectroscopy (CDB). The pick-off annihilation lifetime of ortho-positronium (o-Ps) was progressively shortened by deformation, possibly due to anisotropic elongation of the free volume and enhanced overlap of the o-Ps wavefunction with the surrounding polyethylene molecules. The anisotropy elongation of the free volume in deformed polyethylene was also implied by CDB. The intensity of o-Ps was enhanced in high density polyethylene (HDPE) and ultra-high-molecular-weight polyethylene (UHMWPE) by deformation, but not in low density polyethylene (LDPE). This suggests that the destruction of crystallites may play a significant role in the deformation of HDPE and UHMWPE but not in LDPE. Comparison of the PALS data, obtained with two specimens sandwiching the positron source, with those obtained with a single specimen by using a commercial PALS system recently developed by Yamawaki et al confirmed the usefulness of the commercial PALS system in the study of deformed polymers.
18th International Conference on Positron Annihilation(ICPA2018)

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