A study on relationship between morphology and rheology of immiscible polymer blends with temporal changes in the interfacial area

This study investigated the morphological and rheological changes associated with the temporal evolution of interfacial area in two different processes---(1) coalescence of immiscible polymer blends, and (2) reaction-induced phase separation from an initially homogeneous reactive polymer system.; The importance of various time-scales in the process of coalescence was analyzed considering model processing flows and the flow in a chaotic mixer. It was found that in the case of capillary dies, coalescence takes place predominantly in the zones away from the die wall and the die axis. In the case of mold filling, coalescence of droplets takes place after the molten fluid has traveled a characteristic distance along the mold. It was observed that coalescence not only leads to formation of larger droplets, but also fibrils of high aspect ratio, especially in capillary flows. The time-scale analysis showed that a majority of droplets (in the flow through capillary dies and strip mold) does not coalesce at high shear rate due to insufficient time for drainage.; This study, for the first time, showed that chaotic mixing condition, apart from expediting morphology development, slows down coalescence substantially. Time-periodic flow reorientation present in chaotic mixing frequently alters collision trajectories, and subjects droplet pairs in the midst of drainage process to diverging pathways. It was found that coalescence is subdued at higher degree of chaotic mixing, for high viscosity ratio, and high shear rates.; A phenomenological model based on Lee and Park formalism revealed that the magnitude of interfacial stresses originated from coalescence is an order of magnitude smaller than the viscous stresses associated with fluid phase deformation.; Formation of new phase, phase growth, and temporal changes in viscosity of each phase during polymerization gave rise to characteristic changes in rheological properties in curing of epoxy in polystyrene-epoxy system. It was found that log G' vs. log G″ plots are useful indicators of morphological changes in polystyrene-epoxy system caused by epoxy curing. It was observed that morphological changes and associated rheological signals are strong only in the presence of higher epoxy content, which in turn generated larger interfacial areas.