Protean droplet breakup in porous media

We study quasi-2D oil-in-water droplets stabilized by a surfactant which flow through a microfluidic porous media. The output of this flow are droplets which are highly variable in their sizes, as a result of mergers and breakups. Droplets can merge when they are in high contact with each other, which is especially likely at higher oil volume fractions. Droplets can break up when they collide with a cylindrical obstacle in the microfluidic chamber, which is especially likely when the droplets are large. Therefore, the droplets arrive at a steady-state size distribution, which is a function of the system geometry, flow speeds, and fluid properties. We show how the total size distribution of our droplets changes with distance through our system. We also analyze how and why individual droplets break as a function of these same properties. We find a nondimensional power-law separator for droplet-obstacle collisions that delineates whether the droplet will break up or not, and a description of how the droplet will break.