BRILLOUIN LIGHT-SCATTERING FROM SHEAR-WAVES IN AN EPOXY-RESIN THROUGHTHE GLASS-TRANSITION

The temperature dependences of the characteristic frequency and lifeti me of hypersonic transverse acoustic waves in the epoxy system EPON 82 8 have been probed by means of the Brillouin light scattering techniqu e. Evidence has been found of a very broad dispersion region, together with a discontinuity close to the glass transition temperature T-g. F or temperatures higher than T-g, the shear loss data obtained from Bri llouin spectra are in quantitative agreement with dielectric data for the same system. For lower temperatures, the Brillouin data deviate fr om the dielectric ones, the former being more sensitive to the seconda ry relaxation processes.