Generation of droplet group based on an external electromagnetic valve in a microfluidic chip

Previous studies on droplet generation in microfluidics mainly focus on the monodisperse droplet, but limited attention has paid to the generation of droplet groups composed of multiple droplets with different volumes or components. In this study, a programmable electromagnetic valve is externally connected with the microfluidic chip featuring a conventional flow-focused structure. Different from the previous situation where only one droplet is generated by a single actuation of the electromagnetic valve, by precisely controlling the opening and closing of the valve, the continuous phase fluid exhibits periodic flow in the channel, and we realized the generation of a droplet group by a single actuation of the valve, and the number and volume of the droplets in each group can be regulated. Specifically, the number of large droplets in a droplet group is mainly determined by the opening time of the electromagnetic valve and the two-phase flow rate, and the number of small droplets is dominated by the valve closing time. The volume of individual droplets in a droplet group is largely dependent on the flow rate of the continuous phase. Our study extends the understanding of microfluidic droplet formation. It provides a feasible method for the efficient preparation of polydisperse droplets, which is important for microfluidic chip-based droplet control and has potential applications in industries related to microfluidic droplets.