DYNAMIC CROSSOVER OF CRITICAL-BEHAVIOR IN POLYMER BLEND SOLUTIONS

By the use of quasi-elastic light scattering, dynamic critical behavio r was studied for symmetrical blend solutions of polystyrene/poly(meth yl methacrylate)/deuterated benzene and polystyrene/poly(2-chlorostyre ne)/deuterated benzene having different polymeric indices N and polyme r concentrations c. The decay rate Gamma(I) of polymer-composition flu ctuations showed the dynamic crossover from the diffusive to the mode- mode-coupled hydrodynamic behavior in all solutions. The dynamic-cross over number tau, which represents the distance between the stability limit and the location of the dynamic crossover, was comparable to tha t theoretically expected for the dynamically-unentangled system in the present ranges of N and c including a chain-entangled region. The ble nd solutions with entanglements exhibited a wider mode-mode-coupled re gime than theoretical prediction. The dynamic-crossover number tau wa s larger than the Ginzburg number Gi, which characterizes the location of the static crossover from the mean-field to the nonclassical Ising behavior, and the mode-mode,coupled dynamics covered a wider region t han the statical Ising behavior.