Pinch-off dynamics of an electrohydrodynamic tip streaming jet transforming into the microdroplet

The drop-on-demand electrohydrodynamic (EHD) printing is promising for manufacturing high-resolution dot arrays. Such dot fabrication is commonly achieved through two printing modes (jet/droplet mode), i.e., continuous jet directly flying to or broken jet induced droplet depositing in the substrate. The droplet mode commonly has a higher printing frequency than the jet mode, indicating the droplet mode's advantage in drop-on-demand EHD printing. However, most research on EHD printing focuses on the jet mode, which causes the mechanism of droplet production through jet pinch-off remains unclear. This study employs an arbitrary Lagrangian–Eulerian method capable of getting a sharp interface to reveal the pinch-off mechanism. First, the development of a tip streaming from a meniscus to the pinch-off is analyzed. It is found that the high pressure at the neck is the main reason for the pinch-off of the jet into the droplet. Second, the EHD phase diagram in the parameter space of We–Cae is plotted, where We is the Weber number and Cae is the electric capillary number. Finally, the important influences of the charge relaxation on the EHD tip streaming jet's breakup behavior and the generated droplets' properties are revealed. Evolutions of the droplet's properties, including radius, velocity, and charge, with varying charge relaxation parameters are offered. These properties of the droplet show their relationships with extreme values as a function of the charge relaxation parameter. This work can serve as the theoretical basis for tuning the EHD printing manufacturing performance.