Dynamic rheological behavior and morphology near phase-separated region for a LCST-type of binary polymer blends

The dynamic rheological properties and morphology in the vicinity of phase-separated region for poly(methyl methacrylate) (PMMA)/poly(styrene-co-acrylonitrile) (SAN) blends with lower critical solution temperature (LCST) behavior were investigated. When temperature was above the phase separation temperature, i.e. cloud point (Tc) for some PMMA/SAN blends, the slope of plotting log G ′ versus log ω decreased at low frequencies (terminal region), indicating the appearance of phase-separation and existence of heterogeneous structure. We employed a model dealing with complex modulus of the two phases mixture proposed by Kopnistos et al. for describing the dynamic rheological behaviors of PMMA/SAN blends, according to the assumption that the interfacial tension between the matrix and the dispersed phase was independent of local shear and variation of interfacial area, and that the dispersed spherical droplets were nearly monodispersed. It is found that the predicted results were in qualitative agreement with the experimental data of this study. The ratio of interfacial tension α to the size of dispersed phase R, α/R, was obtained for 80/20 and 60/40 PMMA/SAN blends, and the two different morphology were also observed.