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

TL;DR

This study investigates how physical aging affects the vibrational density of states in a glassy polymer, revealing that aging reduces the boson peak in the low-energy vibrational spectrum.

Contribution

It provides experimental evidence on the impact of physical aging on the low-frequency vibrational states of a polymeric glass, using inelastic neutron scattering.

Findings

Aging decreases the boson peak in the VDOS.

Long-term annealing at below Tg reduces low-energy vibrational states.

Quenching from above Tg results in different vibrational characteristics.

Abstract

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 Tg, and another was quenched from a temperature higher than Tg. It was found that the VDOS around the boson peak, relatively to the one at higher energy, decreases with the annealing at lower temperature than Tg, i.e., with the physical aging.