Morphology evolution of immiscible polymer blends in complex flow fields

A transparent flow cell apparatus has been used to obtain quantitative info rmation on the morphology evolution of a model polymer blend flowing in com plex Row fields. A dilute emulsion of poly-dimethylsiloxane droplets immers ed in a poly-isobutene matrix, both Newtonian liquids at room temperature, has been chosen as a model system. Optical microscopy coupled with image ac quisition analysis allowed to monitor the behavior of droplets flowing thro ugh a sudden contraction and through a gradual converging channel followed by a sudden expansion. The experimental results indicate that drop deformat ion and breakup are sensitive to both shear and extensional components. A s imple criterion, based on the evaluation of a local critical capillary numb er, is proposed to predict the morphological evolution of the flowing blend . By using computer simulations to estimate the velocity gradients in the f low field, it is shown that the proposed criterion is able to successfully predict the observed morphology. (C) 2001 Elsevier Science Ltd. All rights reserved.