Experimental study on electric-field-induced droplet generation and breakup in an immiscible medium

Electrical manipulation technique to produce qualified size of droplets has received substantial attention due to its wide applications in biology, medicine and chemistry, where the droplet behaviors could be controlled by adjusting external parameters. Characterization of charged droplet generation and breakup processes is crucial for understanding the basic mechanism of droplet manipulation. In this paper, the formation and breakup processes for charged droplets in dielectric immiscible oil were investigated experimentally at micro-scale by utilizing high-speed photography. The droplet behaviors at the ambient of needle orifice were visualized and captured at various electric field strengths and flow rates while its generation and motion characteristics were analyzed. Novel formation process of micro-droplets emitted from arrayed jets was found and depicted in detail when violent liquid breakup occurred at high voltage. Furthermore, the relationships of electric field and flow rate with characteristics of charged droplet behavior were quantitatively discussed. By consideration of electric field and flow rate, a scaling law to predict droplet size distributions was derived. Besides, a dimensionless model to predict charged droplet positions was given, which showed a linear increasing trend with electric field and time.