SYNCHROTRON SAXS STUDY OF PHASE-SEPARATION KINETICS IN A POLY(2-CHLOROSTYRENE) POLYSTYRENE BLEND

The concentration fluctuations in a poly(2-chlorostyrene)/polystyrene (P2ClS/PS) blend and their changes induced by temperature jumps were s tudied using time-resolved synchrotron small-angle X-ray scattering (S AXS). The virtual structure factor, which represents a formal extensio n of the one-phase equilibrium structure factor into the two-phase reg ion, has been obtained from the mean-field static susceptibilities mea sured in the one-phase region. Three sets of measurements at different jump temperatures (from 140-degrees-C to 156.87-degrees-C, to 166.96- degrees-C, and then to 179.91-degrees-C) were performed. In the metast able region (142-167-degrees-C) the experiments indicate that the init ial kinetics can be described by the theory developed by Binder, with relaxation times of chain molecules being in a scale of minutes. The v alues are comparable with the results of the self-diffusion coefficien t (on the order of approximately 10(-15) cm2 s-1) of poly(bromostyrene )/polystyrene blends measured in the molten state. In the small scatte ring wave vector q range the initial relaxation rates of concentration fluctuations increased with increasing q in accordance with theoretic al predictions. However, the relaxation process did not clearly follow a simple exponential law. The relaxation rate became slower with incr easing time. In the case of a deeper jump (at 179.91-degrees-C), the r elaxation rate changed its sign from positive to negative, with the co ncentration fluctuations growing and eventually leading to phase separ ation.