Droplet traffic in microfluidic networks: Role of droplet collisions and occlusion

The dynamics of droplet flows in microfluidic loop networks are governed by the frequency at which the droplets enter the loop. At low frequencies, droplets always choose the channel with lower hydrodynamic resistance, and droplets interact indirectly through their modifications to resistance of the channels. As the droplet frequency increases, direct droplet-droplet interactions in the junction also contribute to droplet decisions and may force the droplets to the channels with higher hydrodynamic resistance. Collisions are considered the main type of direct interaction between droplets. However, our study suggests that occlusion of the entrance of the channel by droplets also impacts their decisions, even when there is no collision and contact. We study droplet decision rules by use of droplet trajectories and distribution of the droplets in the junction and throughout the network. Also, application of machine learning techniques to identify decision rules and predict the droplet decisions is studied.