Effect of the elastic properties modification on the vibrational density of states: a joint Brillouin and Raman scattering study

The modification of the vibrational density of states in a reactive epoxy-amine mixture during isothermal polymerization have been characterized by Brillouin and Raman scattering measurements at different temperatures. During the reaction the system undergoes the glass transition passing from the liquid to the glassy phase. The relative variation of the boson peak and the elastic moduli have been investigated. We find that the intensity variation and the shift of the boson peak are only an apparent effect due to the elastic medium transformation. A master curve of the spectra in the boson peak region can always be obtained both as a function of the reaction temperature and as a function of the reaction time. Moreover, the Brillouin light scattering results give evidence of the validity of a Cauchy-like relation for the real part of the elastic moduli measured at finite frequencies also in relaxing liquids.