Rheo‐Optical behavior of binary polymer blends: The effect of simple shear flow on phase behavior

Abstract

AbstractThe phase behavior of polymer blends under simple shear flow has been studied using a custom‐designed rheo‐optical system consisting of a two‐dimensional small‐angle light scattering (SALS) device incorporated into a conventional rheometer. Two‐dimensional SALS images were gathered for model polymer blend systems with different quiescent phase behavior: polystyrene/polyisobutylene (PS/PIB) that exhibits upper critical solution temperature phase behavior and polystyrene/poly(vinyl methyl ether) (PS/PVME) that shows lower critical solution temperature phase behavior. For the PS/PIB blend, shear‐induced phase mixing occurred at a critical shear rate. Below that critical shear rate, the dispersed phase was highly elongated parallel to the flow direction. For PS/PVME blends, a streak scattering pattern was observed even though the sample became optically clear after shearing. We observed, apparently for the first time, the development of a bright‐streak pattern from a transient dark‐streak pattern for a polymer blend system under shear. Rheo‐microscopy studies revealed an intriguing wave pattern that developed coincident with the observation of a streak pattern by SALS. The relationship between the two phenomena has not yet been established.