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-i nduced miscibility of polymer blends actually result from a ''true'' s hift of the critical temperature. To elucidate the origin of the pheno menon more clearly, we have investigated the structural changes of pha se 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-ac rylonitrile)/poly(meth methacrylate), which exhibits LCST type phase b ehavior. Rheo-SALS (small angle light scattering) was used to probe th e time-dependent structure evolution during shear flow. Quenched sampl es were examined with TEM and phase contrast light microscopy, and the Fourier transforms of digitized micrographs were compared with two-di mensional light scattering measurements of the same samples. The blend s were also subjected to pressure-driven flows and drag flows at very high stresses, and their morphology was similarly studied. The structu re evolution due to flow could be explained by hydrodynamic effects co nsistent with droplet breakup theory.