THE SEGMENTAL AND ROTATIONAL DYNAMICS OF PPO, ABOVE THE GLASS-TRANSITION, INVESTIGATED BY NEUTRON SCATTERING AND MOLECULAR DYNAMICS SIMULATIONS

摘要

The relaxation properties of poly(propylene oxide) at temperatures above the glass-transition temperature are studied by quasi-elastic neutron scattering and molecular dynamics (MD) simulations. The contributions to the dynamic structure factor from the segmental motion and the methyl group jump rotation are separated using a threefold jump-rotation model for the methyl side group motion, with a delta function for the distribution of relaxation times, and a stretched exponential function for the segmental motion. This simple model describes momentum transfer and time dependence of the data over a wide temperature range. The results show that with this separation, both neutron and MD data can be well described, and the analysis of both contributions is necessary in order to obtain reliable results for the segmental relaxation and rotational relaxation times at temperature above T_g.