Morphology evolution of immiscible polymer blends in complex flow fields

A transparent flow cell apparatus has been used to obtain quantitative information on the morphology evolution of a model polymer blend flowing in complex flow fields. A dilute emulsion of poly-dimethylsiloxane droplets immersed in a poly-isobutene matrix, both Newtonian liquids at room temperature, has been chosen as a model system. Optical microscopy coupled with image acquisition analysis allowed to monitor the behavior of droplets flowing through a sudden contraction and through a gradual converging channel followed by a sudden expansion. The experimental results indicate that drop deformation and breakup are sensitive to both shear and extensional components. A simple criterion, based on the evaluation of a local critical capillary number, is proposed to predict the morphological evolution of the flowing blend. By using computer simulations to estimate the velocity gradients in the flow field, it is shown that the proposed criterion is able to successfully predict the observed morphology.