Droplet traffic regulated by collisions in microfluidic networks

We study droplet traffic at the inlet node of an asymmetric microfluidic loop. We observe that collisions between successive droplets may occur at the junction. We show that this phenomenon has an impact on the repartition of the droplets in the arms of the loop since it modifies the nature of the collective hydrodynamic feedback mechanism that usually regulates traffic. We present a robust indirect method to measure the excess hydrodynamic resistance added by each droplet to a microfluidic channel, and we rationalize our experimental finding using simple physical arguments.