Dynamics of density fluctuations of a glass-forming epoxy resin revealed by Brillouin light scattering

Brillouin light scattering is used for studying the spectrum of density flu ctuations of the glass-forming epoxy resin diglycidyl ether of bisphenol-A. Spectra at different temperatures ranging from the glassy to the liquid ph ase are obtained from a direct subtraction of depolarized from polarized sp ectra. In addition to the structural relaxation, evidence is given of a fas t secondary relaxation process, which affects Brillouin spectra also at tem peratures lower than that of the glass transition T-g. For the elaboration of isotropic spectra, we exploit the possibility of using the same relaxati on function gained from dielectric spectra taken from the same sample. The temperature behavior of the relaxation strength shows the existence of an o nset for the structural relaxation, located at a temperature about 93 K hig her than T-g, consistent with the results of previous dielectric spectrosco py and depolarized light scattering investigations. The role of secondary r elaxations of intramolecular nature in the mode-coupling analysis of real g lass formers is also discussed.