Local Motion in the beta-Transition Range of Partially Crystalline Polyethylene Studied by Neutron-Scattering

Abstract

We have performed inelastic neutron scattering experiments on protonated and fully deuterated partially crystalline polyethylene. Using a high-resolution, three-axes spectrometer with an energy resolution of 80 mu eV, it was possible to detect a quasielastic process in the dynamic structure factor with a FWHM of 0.3meV. This process was shown to be active above T-0 = 260 K and its FWHM was nearly independent of temperature and scattering vector. The spatial extent of the underlying motional process was determined from the corresponding Debye-Waller factor. The mean squared displacement increases strongly with T above T-0 up to 4 Angstrom(2) at T = 380 K. Comparison with results from similar work on fully amorphous polymers suggests to relate T-0 to the glass transition of the amorphous phase in partially crystalline polyethylene. The coherent structure factor shows no evidence for a significant contribution of correlated motion to the process. A speculative explanation of the observed phenomenon as a non-equilibrium soft-mode is proposed.