Dynamics of density fluctuations of a supercooled epoxy resin revelead by Brillouin light scattering

Brillouin light scattering is used for studying the spectrum of density fluctuations of the glass-forming epoxy resin diglycidyl ether of bisphenol-A. Spectra at different temperatures ranging from the glassy to the liquid phase are obtained from a direct subtraction of depolarized from polarized spectra. In addition to the structural relaxation, evidence is given of a fast secondary relaxation process, which affects Brillouin spectra also at temperatures lower than that of the glass transition Tg . For the elaboration of isotropic spectra, we exploit the possibility of using the same relaxation function gained from dielectric spectra taken from the same sample. The temperature behavior of the relaxation strength shows the existence of an onset for the structural relax- ation, located at a temperature about 93 K higher than Tg , consistent with the results of previous dielectric spectroscopy and depolarized light scattering investigations. The role of secondary relaxations of intramolecu- lar nature in the mode-coupling analysis of real glass formers is also discussed.