Use of a cooperative-motion domain model to analyze Brillouin light scattering measurements of the dynamic modulus in triblock copolymers

The use of the relaxation function is widespread in the study of polymer dy namics. Since the popular empirical KWW relaxation function consistently un derestimates dielectric loss at high frequency, several models dealing expl icitly with intermolecular cooperativity have been proposed as alternatives . In this article, the domain model proposed by Matsuoka, previously used o nly to analyze dielectric relaxation results, is used to analyze Brillouin light scattering results from polystyrene-polybutadiene-polystyrene tribloc k. copolymers. A single relaxation time analysis and the KWW model are both compared to the domain model. Neither of these models fits the Brillouin d ata well. The single relaxation time analysis gives a physically unrealisti c results; the KWW analysis fits the data at low frequency, but fails in th e high-frequency region by underestimating the attenuation. The domain mode l fits the Brillouin data well over the entire temperature/frequency range. The results show that in order to understand the full range of dynamics in these materials and in polymeric materials in general, the KWW model is in sufficient due to its underestimation of attenuation at high frequency. A m odel including cooperative motion is crucial to fully understand polymer dy namics. (C) 2000 John Wiley & Sons, Inc.