LOCALIZED FAST RELAXATION IN POLY(METHYL METHACRYLATE) GLASS

Fast relaxational motions in glassy PMMA were investigated through qua sielastic neutron scattering. As previously found with quasielastic li ght scattering, the corresponding relaxation time, which is of the ord er of 10(-11) s, is only slightly temperature dependent, while the rel axational signal intensity increases rapidly with temperature. To eluc idate the origin of this behavior, comparison is made between the non- linearly temperature-dependent part of the mean-square displacement an d the hole volume fraction, as determined by positron annihilation lif etime spectroscopy. These two quantities appear to be strongly correla ted. A model, which takes into account the presence of holes in the gl assy matrix, is proposed to explain the Debye-Waller factor behavior.