Droplet pair breakup in microfluidic expansion channel

Abstract

Previous studies on droplet splitting mainly focus on monodisperse droplets, and the understanding of the breakup of polydisperse droplet systems is still lacking. In this work, we experimentally study the breakup of droplet pairs in the expansion region of microfluidic channel. The results show that with the increase in the size ratio of the droplets in the droplet pair, the breakup mode of droplet pairs changes from rear droplet breakup to front droplet breakup, and then to front droplet alternate breakup. The expansion angle can affect the critical size ratio of the splitting mode transition, but it cannot change the transition trend. The expansion angle plays a major role in the splitting time and distance of the droplet pair. When the expansion angle is increased, the splitting time of the droplet pair is reduced and the splitting distance is shorter. Our study extends the understanding of the breakup of non-monodisperse droplet systems and provides a feasible approach for the selective and controllable splitting of droplets, which is important for laboratory-on-a-chip droplet volume manipulation and has potential applications.