DYNAMICS OF POLYBUTADIENE ABOVE THE GLASS-TRANSITION STUDIED BY BRILLOUIN LIGHT-SCATTERING

Brillouin-light-scattering measurements have been performed on both bulk and thin supported polybutadiene (PB) films, in the frequency range 1-300 GHz. The results obtained on the relaxation behavior of PB have been interpreted in the framework of the mode-coupling theory and compared with neutron spin-echo data relative to the same system. For temperatures higher than the critical temperature T(c), a quantitative agreement of the mean relaxation time with the viscosity time scale has been found, together with the validity of a time-temperature scaling law. For temperatures approaching the glass transition, a departure of relaxation time from the viscosity time scale has been observed. This phenomenon has been attributed to a decoupling between structural and secondary relaxation processes.