CRITICAL-BEHAVIOR OF ASYMMETRIC POLYMER BLEND SOLUTIONS - POLY(METHYLMETHACRYLATE) POLY(DIMETHYL SILOXANE) SOLVENT

By means of light scattering, static and dynamic critical behavior was investigated for polymer blend solutions consisting of two polymers w ith highly asymmetric polymeric indices, that is, poly(methyl methacry late)/poly(dimethyl siloxane)/benzene and poly(methyl methacrylate)/po ly(dimethyl siloxane)/toluene solutions. Isothermal susceptibility S-T and correlation length xi in the benzene solution showed Fisher's ren ormalized Ising behavior characteristic to ternary mixtures in the ver y limited region near the stability limit. On the contrary the toluene solution exhibited the renormalized behavior over the wide temperatur e range, reflecting asymmetric phase behavior arising from solvent sel ectivity of toluene. The temperature dependence of the critical-fluctu ation decay rate Gamma for both solutions exhibited ''quasihydrodynami c'' behavior far from the stability limit. which became the macroscopi c hydrodynamic behavior with temperature approaching the critical poin t. We also measured the tracer-diffusion coefficient D-t of constituen t polymers by pulsed-field-gradient nuclear magnetic resonance (NMR) t o demonstrate that the quasihydrodynamic behavior may come from the dy namic asymmetry, i.e., difference in the translational mobility of Bro wnian motions between component molecules. (C) 1998 American Institute of Physics. [S0021-9606(98)51710-2].