COMPOSITION FLUCTUATION EFFECTS ON DIELECTRIC NORMAL-MODE RELAXATION IN DIBLOCK COPOLYMERS .1. WEAK SEGREGATION REGIME

Dielectric relaxation spectroscopy has been used to investigate the no rmal-mode relaxation in disordered diblock copolymer melts far from th e order-to-disorder transition (ODT). The dielectric spectra are analy zed in order to quantitatively obtain the distribution of relaxation t imes in the disordered diblocks. The width of the relaxation function shows significant broadening relative to the respective homopolymer di stributions when the temperature is decreased and/or the molecular wei ght is increased. The broadening is attributed to composition fluctuat ion effects on the normal-mode relaxation. These effects are theoretic ally accounted for by considering both the short-range fluctuations du e to chain connectivity and the long-range concentration fluctuations in diblock copolymers due to the proximity to the ODT and their coupli ng to the individual block segmental dynamics. Theory not only capture s the relative features of the distributions but also quantitatively c ompares very well with the experimental dielectric spectra.