SYNCHROTRON SAXS STUDY OF MEAN FIELD AND ISING CRITICAL-BEHAVIOR OF POLY(2-CHLOROSTYRENE) POLYSTYRENE BLENDS

Synchrotron small-angle X-ray scattering (SAXS) of poly(2-chlorostyrene)/polystyrene (P2ClS/PS) blends in the immediate neighborhood of the critical mixing point can be achieved by first locating the critical mixing point precisely. By combining a phase volume method with SAXS, the critical moving point for P2ClS(M(w)=2.33X10(5),M(w)/M(n)=1.19)/PS(M(w)=3.7x10(4),M(w)/M(n)<1.06) in the presence of 22.6wt% di-n-butyl phthalate was found to have a critical weight fraction of PS, W(PS,c) = 0.52. A lower critical mixing temperature T(c) = 134.30-degrees-C, where W(PS) + W(P2ClS) was set to equal one, could clearly reveal a crossover in the static susceptibility and the correlation length from mean field to Ising-like behavior, with critical exponents gamma changing from 1.00 (mean field) to 1.23 (Ising) and nu changing from 0.50 (mean field) to 0.63 (Ising). The crossover occurs at 2.6 K below the critical mixing temperature.