RHEOOPTICAL BEHAVIOR OF BINARY POLYMER BLENDS - THE EFFECT OF SIMPLE SHEAR-FLOW ON PHASE-BEHAVIOR

The phase behavior of polymer blends under simple shear flow has been studied using a custom-designed rheo-optical system consisting of a tw o-dimensional small-angle light scattering (SALS) device incorporated into a conventional rheometer. Two-dimensional SALS images were gather ed for model polymer blend systems with different quiescent phase beha vior: polystyrene/polyisobutylene (PS/PIB) that exhibits upper critica l solution temperature phase behavior and polystyrene/poly(vinyl methy l ether) (PS/PVME) that shows lower critical solution temperature phas e behavior. For the PS/PIB blend, shear-induced phase mixing occurred at a critical shear rate. Below that critical shear rate, the disperse d phase was highly elongated parallel to the flow direction. For PS/PV ME blends, a streak scattering pattern was observed even though the sa mple became optically clear after shearing. We observed, apparently fo r the first time, the development of a bright-streak pattern from a tr ansient dark-streak pattern for a polymer blend system under shear. Rh eo-microscopy studies revealed an intriguing wave pattern that develop ed coincident with the observation of a streak pattern by SALS. The re lationship between the two phenomena has not yet been established.