Electrowetting-actuated Coalescence-Induced droplet jumping with square pulse signal

Electrowetting/dewetting is a highly efficient method with broad application prospects. However, the potential of using electrowetting to control droplet coalescence-induced jumping remains underexplored. In this work, electrowetting-actuated coalescence-induced droplet jumping with square pulse signal of Galinstan and water droplets was numerically investigated. The droplet jumping velocity enhancement was due to two mechanisms: the electro-wetting/dewetting enhancement mechanism and the coalescence enhancement mechanism. According to the coupling effect of two mechanisms, we defined three distinct modes: synergistic enhance mode, antagonistic enhance mode, and suppress mode. The mode phase diagram was systematically mapped to pulse width and initial voltage. The effect of pulse widths on the droplet jumping velocity was quantitatively investigated, revealing a sinusoidal oscillation behavior with gradually attenuating amplitude as the pulse width increased. The results reveal that, in the first period, an intermediate pulse width maximizes the jumping velocity and jumping efficiency, while excessively long pulses decrease additional surface energy and increase viscous dissipation, thereby suppressing jumping. A maximum normalized jumping velocity is obtained when the pulse width equals the spreading time, v* = 0.85 and v* = 0.84 for Galinstan and water droplets, which achieved the highest normalized coalescence-induced droplet jumping velocity currently. Furthermore, it was demonstrated that the contact time scales exponentially with pulse width for Galinstan and water droplets, and an empirical correlation was derived accordingly. Finally, an energy balance analysis and investigations of the pressure and velocity field were carried out to reveal the underlying mechanism of electrowetting-actuated coalescence-induced jumping behavior.