Inelastic neutron and Raman scattering of poly(methyl methacrylate): Nanostructure of polymer glasses

Low-energy excitations were investigated in amorphous poly(methyl methacrylate) by means of both neutron and Raman scatterings, in a wide temperature interval. The frequency dependence of the light-vibration coupling coefficient was deduced, especially at low temperature where the quasi-elastic contribution is not significant; it was not found to be linear. The vibrational density-of-states anomaly is interpreted in the frame of a non-continuous glassy nanostructure, which is characterized by a log-normal size distribution of domains.