Shear flow effect on phase behavior and morphology in polymer blends

The effect of simple shear flow on the phase behavior and morphology was in vestigated for both polystyrene/poly(vinyl methyl ether) (PS/PVME) and poly (methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN-29.5) blends , which have LCST (lower critical solution temperature)-type phase diagram. The measurements were carried out using a special shear apparatus of two p arallel glass plates type. The PS/PVME blends showed shear-induced demixing and shear-induced mixing at low and high shear rate values, respectively. In addition, the rotation speed and the sample thickness were found to have a pronounced effect on the phase behavior under shear now. On the other ha nd, PMMA/SAN blend showed only shear-induced mixing and the magnitudes of t he elevation of the cloud points were found to be composition and molecular weight dependent. The morphology of the PMMA/SAN=75/25 blend indicated tha t shear-induced mixing occurred at a critical shear rate value, below which the two phases were highly oriented and elongated in the flow direction.