Effect of shear flow on the morphology and phase behavior of a near-critical SAN/PMMA blend

An ongoing debate concerns whether experimental observations of flow-induced miscibility of polymer blends actually result from a "true" shift of the critical temperature. To elucidate the origin of the phenomenon more clearly, we have investigated the structural changes of phase domains of a number of polymer blends under the influence of flow. The most recent study used a near-critical blend of poly(styrene-co-acrylonitrile)/poly(meth methacrylate), which exhibits LCST type phase behavior. Rheo-SALS (small angle light scattering) was used to probe the time-dependent structure evolution during shear flow. Quenched samples were examined with TEM and phase contrast light microscopy, and the Fourier transforms of digitized micrographs were compared with two-dimensional light scattering measurements of the same samples. The blends were also subjected to pressure-driven flows and drag flows at very high stresses, and their morphology was similarly studied. The structure evolution due to flow could be explained by hydrodynamic effects consistent with droplet breakup theory.