Viscoelastic effects in dynamics of concentration fluctuations in dynamically asymmetric polymer blends

Relaxation processes of the concentration fluctuations induced by a rapid pressure change were investigated for a dynamically asymmetric polymer blend (deuterated polybutadiene (DPB) / polyisoprene (PI)) with a composition of 50/50 by weight in one phase region by using time-resolved small-angle neutron scattering. The theoretical analysis yielded the wave-number q-dependence of Onsager kinetic coefficient which is characterized by a q^-2-dependence at qξ_ve >1 with the characteristic length ξ_ve being much larger than radius of gyration of DPB or PI. The estimated ξ_ve agrees well with that calculated using the theory by Doi & Onuki, which takes into account viscoelastic effects.