Self-excited electrowetting of a falling droplet without direct electrode contact

The direct electrical contact is strictly required in traditional electrowetting, which severely restricts its application in free-falling droplet scenes. Here, a self-excited electrowetting phenomenon without electrode contact is reported, thereby departing from the conventional electrowetting configuration. A falling droplet is deformed in an electric field, triggering corona discharge. An equivalent circuit is thus established, resulting in wetting enhancement. A framework based on discharge theory and residence time is established to predict this effect, which is determined as 0.64 ≤ E* ≤ 1.14 and We ≤ 30.88, and is verified by the experiments. These findings offer insights into the spreading control of dynamic deposition processes, such as electrostatic spraying and inkjet printing.