Synchrotron small-angle X-ray scattering of relaxation process in a nonentangled diblock copolymer

The time changes in the scattered intensity induced by a pressure jump within the disordered state of nonentangled poly(styrene-block-isoprene) were measured by using time-resolved synchrotron small-angle X-ray scattering. It was found that the time changes in the scattered intensity could be approximated by the Cahn-Hilliard-Cook linearized theory. The analyses yielded the wavenumber q dependence of the Onsager coefficient of the block copolymer. We compared our result the Debye function Lambda(q) = 2 Lambda(0)[q(2)R(Lambda)(2) + exp(-q(2)R(Lambda)(2)) - 1]/q(4)R(Lambda)(4) as proposed by Fredrickson, where R-Lambda is the radius of gyration of the block copolymer.