Effect of Polymerization on the Boson Peak, from the Liquid to Glassy Phase

TL;DR

This study investigates how polymerization affects the vibrational density of states and the boson peak in a reactive epoxy-amine mixture, revealing that elastic medium changes explain peak shifts while structural modifications do not alter excess vibrational states.

Contribution

It provides new insights into the relationship between polymerization, elastic properties, and vibrational states in glass-forming materials.

Findings

Boson peak shift and intensity decrease are due to elastic medium modifications.

Bond formation does not change the excess vibrational states over the Debye level.

Elastic properties evolve during polymerization, influencing vibrational spectra.

Abstract

Raman scattering measurements are used to follow the modification of the vibrational density of states in a reactive epoxy{amine mixture during isothermal polymerization. Combining with Brillouin light and inelastic x-ray scattering measurements, we analyze the variations of the boson peak and of the Debye level while the system passes from the uid to a glassy phase upon increasing the number of covalent bonds among the constituent molecules. We find that the shift and the intensity decrease of the boson peak are fully explained by the modification of the elastic medium throughout the reaction. Surprisingly, bond-induced modifications of the structure do not affect the relative excess of states over the Debye level.