Experimental study on millimeter-scale W1/O/W2 compound droplets formation in a co-flowing device with two-step structure

Compound Droplet Generation by a Hybrid Microfluidic Device

Microfluidic technology based on a compound droplet plays an increasingly significant role in different disciplines, such as genetic detection, drug transportation, and cell culture. Low-cost, stable, and rapid methods to produce compound droplets are more and more in demand. In this paper, a hybrid 3D-printed microfluidic device was designed to realize efficient fabrication of multicore compound droplets, where a first oil phase (O1) is cut by a water phase (W) to form pure O1 droplets, and then the W phase containing O1 droplets is cut by a second oil phase (O2) to generate multicore compound droplets. A series of experiments were conducted to determine the influence of the flow rate and viscosity on the formation dynamics of compound droplets. It is found that the number of inner cores is mainly affected by the W and O2 phases, and a W phase with higher viscosity and a higher flow rate is more likely to produce compound droplets with more inner cores. This work provides new insights into the formation dynamics of compound droplets and can contribute to the optimization of emulsion production.