Polymer Engineering Faculty Research

Structure Evolution and Phase Behavior of Polymer Blends Under the Influence of Shear

Robert Weiss, The University of Akron


The effect of shear flow on the phase behavior, structure formation and morphology of a near-critical composition blend of poly(styrene-co-acrylonitrile)/poly(methyl methacrylate) (SAN/PMMA) and an off-critical composition blend of SAN/poly(ε-caprolactone) (SAN/PCL) were investigated. Both blends exhibited lower critical solution temperature (LCST) behavior. Rheo-SALS (small angle light scattering) was used to characterize the time-dependent structure evolution during flows with shear rates from 0.01 to 0.05 s−1 and stresses from 8 to 60 kPa. Two types of transient “dark-streak” scattering patterns were observed. One featured a dark streak that diverged with increasing scattering vector, q, which corresponded to a chevron-like structure in the morphology of the blend. The other type of dark streak converged with increasing q, and may be due to a spinodal structure that was stretched in the flow direction. A capillary viscometer was used to achieve shear stresses as high as 400 kPa for the SAN/PCL blends, and microscopy analysis of microtomed extrudates revealed a dispersed phase morphology of cylindrical PCL-rich domains highly oriented in the flow direction. No shear-induced phase transitions were observed for either blend for the range of shear stress studied.