@article {155566, title = {Droplet breakup in flow past an obstacle: A capillary instability due to permeability variations}, journal = {Epl}, volume = {92}, number = {5}, year = {2010}, pages = {54002}, abstract = {In multiphase flow in confined geometries an elementary event concerns the interaction of a droplet with an obstacle. As a model of this configuration we study the collision of a droplet with a circular post that spans a significant fraction of the cross-section of a microfluidic channel. We demonstrate that there exist conditions for which a drop moves completely around the obstacle without breaking, while for the same geometry but higher speeds the drop breaks. Therefore, we identify a critical value of the capillary number above which a drop will break. We explain the results with a one-dimensional model characterizing the flow in the narrow gaps on either side of the obstacle, which identifies a surface-tension-driven instability associated with a variation in the permeability in the flow direction. The model captures the major features of the experimental observations. Copyright (C) EPLA, 2010}, url = {https://iopscience.iop.org/article/10.1209/0295-5075/92/54002}, author = {Protiere, S. and Bazant, M. Z. and Weitz, D. A. and H.A. Stone} }