Effect of physical aging on the low-frequency vibrational density of states of a glassy polymer

The effects of the physical aging on the vibrational density of states (VDOS) of a polymeric glass is studied. The VDOS of a poly( methyl methacrylate) glass at low energy (< 15 meV), was determined from inelastic neutron scattering at low temperature for two different physical thermodynamical states. One sample was annealed during a long time at temperature lower than T-g, and another was quenched from a temperature higher than T-g. It was found that the VDOS around the boson peak, relatively to the one at higher energy, decreases with annealing at lower temperature than T-g, i.e., with the physical aging.