Brillouin light scattering from shear waves in an epoxy resin through the glass transition

The temperature dependences of the characteristic frequency and lifetime of hypersonic transverse acoustic waves in the epoxy system EPON 828 have been probed by means of the Brillouin light scattering technique. Evidence has been found of a very broad dispersion region, together with a discontinuity close to the glass transition temperature T-g. For temperatures higher than T-g, the shear loss data obtained from Brillouin spectra are in quantitative agreement with dielectric data for the same system. For lower temperatures, the Brillouin data deviate from the dielectric ones, the former being more sensitive to the secondary relaxation processes.