The phase structure and phase behavior of polymer blends undergoing simple shear flow

The effect of simple shear flow on the phase structure and phase behavior of polymer blends was studied using a custom-built rheo-optical instrument which consisted of a commercial rheometer and a two-dimensional light scattering device. The scattered light intensity was detected using a high resolution two-dimensional charge coupled device (CCD) detector. This instrument allowed simultaneous rheological and light scattering studies to be performed.^ When simple shear flow was applied to a phase-separated polymer blend, a bright-streak scattering pattern was observed as for many other polymer mixtures reported in the literature. Further studies showed that the bright streak pattern developed from H-shaped and dark-streak patterns. Comparison of light scattering patterns with micrographs of a sheared sample revealed that all scattering patterns were parts of a distorted spinodal ring scattering pattern.^ The rheo-optical experiments showed that the spinodal-type bicontinuous structure was stretched in the flow direction, and a spinodal ring in the light scattering pattern was correspondingly shrunk in the flow direction. The characteristic dimensions of the phase structure of a flowing polymer blend were calculated from the distorted spinodal scattering ring.^ The phase separation kinetics of a flowing polymer blend was also studied. Anisotropic phase separation was observed. H-shaped and dark-streak scattering patterns developed during the phase separation process. The domain growth was studied from the development of scattering patterns.^ Two polymer blend systems were studied in this research: polystyrene/poly-(vinyl methyl ether) and polybutadiene/polyisoprene.