COMPOSITION FLUCTUATION-INDUCED DEPOLARIZED RAYLEIGH-SCATTERING FROM DIBLOCK COPOLYMER MELTS

Dynamic light scattering in the depolarized geometry has been used to investigate the pretransitional behavior of diblock copolymer melts near the order-disorder transition (ODT). Besides the segmental orientational dynamics, an additional slow relaxation process contributes to the dynamic depolarized intensity. This new relaxation mode exhibits an almost exponential shape, a wave vector (q) independent relaxation rate, and a strongly temperature dependent amplitude that compares with the temperature dependence of the maximum of the static structure factor at q(*), measured with small-angle x-ray scattering. An account for the characteristics of this new relaxation process is based on the coupling between orientation and order parameter fluctuations. The depolarized intensity is due to orientation and/or extension of the copolymer chains in the pretransitional state above the ODT, with the relevant length scale of the slow orientation fluctuations being close to 2 pi/q(*).