Time-Resolved Small-Angle Neutron Scattering in Intermediate-and Late-Stage Spinodal Decomposition of DPB/HPI Blends

Time-resolved small-angle neutron scattering (SANS) experiments were performed to study the later stage (i.e., the intermediate stage and the late stage) of spinodal decomposition (SD) of a critical mixture of perdeuterated polybutadiene (DPB) and protonated polyisoprene (HPI) with an LCST-type phase diagram and a critical temperature T_c = 36.1 °C. Time-sliced SANS intensity, S(q,t), is generally composed of the scattering due to growing domains, I_d(q,t), and that due to the thermally induced local composition fluctuations inside the domain I_T(q,t) where q and t are the scattering vector and time, respectively. S(q,t) as a function of q shows the “spatial crossover” such that at q much below and above a time-dependent wave-number, q,(t), it depends only on I_d(q,t) and I_T(q,t), respectively. The time evolution of the composition difference between the two coexisting domains, ΔΦ(t), was determined from I_T(q,t), which was found to be consistent with the prediction of the scattering theory based upon the random-phase approximation. ΔΦ(t) was found to increase with t and reach a constant equilibrium value ΔΦ_e at t > t_cr, where t_cr is the crossover time from the intermediate to the late-stage SD. The crossover wavenumber, q_s(t), also underwent a characteristic change at t_cr.