Effects of Shear Flow on Viscoelastic Properties of Polystyrene/Poly(vinyl methyl ether) Blends near the Phase Separation Temperature

Viscoelastic properties of polystyrene/poly(vinyl methyl ether) blends with nearly critical compositions were measured under steady-shear flows near the phase separation temperatures. In the homogeneous region, shear rate dependences of shear viscosity η and shear compliance J_S are practically the same as those of homopolymers. In the phase-separated region at quiescence, on the other hand, η and J_S are enhanced at low shear rates, but they become almost the same as those in the homogeneous region when the shear rates are higher than their respective critical shear rates. The critical shear rate values from J_S, γ_cJ, were found to be larger than those from η, γ_cV, and γ_cJ is considered to be almost equal to the critical shear rate for shear-induced homogenization γ_c. Moreover, it was pointed out that, when γ_cV is smaller than the critical shear rate for non-Newtonian behavior of η, there exists a plateau region in the shear rate dependence of η.