BRILLOUIN-SCATTERING FROM BULK POLYBUTADIENE - DISTRIBUTION OF RELAXATION-TIMES VERSUS SINGLE RELAXATION-TIME APPROACH

Two different approaches are usually employed to analyse hypersonic data: a non-exponential density relaxation function g(t) with a non-Arrhenius tau(T) versus an exponential g(t) with an Arrhenius temperature dependence of the longitudinal relaxation time tau(T). In this report we provide strong evidence that spontaneous Brillouin scattering alone cannot discriminate between the two approaches. The knowledge Of tau(T), which is of primary importance for this problem, results from complementary ultrasonic and photon correlation experiments on the same sample. We report evidence that the distribution of relaxation times in polybutadiene becomes narrower with increasing T in agreement with experiments and theoretical predictions.