Droplet ejection by electrowetting actuation

TL;DR

This paper investigates how electrowetting-induced contact-line motion causes droplet ejection, deriving a theoretical model and experimentally verifying the criteria for satellite droplet formation across various conditions.

Contribution

It introduces a new theoretical model for droplet ejection criteria under electrowetting and validates it experimentally for different viscosities, sizes, and voltages.

Findings

Ejection size and timing depend on contact-line velocity and ejection dynamics.

Theoretical criteria for droplet ejection are validated experimentally.

Electrowetting parameters can be tuned to control droplet ejection.

Abstract

Fast contact-line motion of a droplet spreading on a solid substrate under the electrowetting effect generates strong capillary waves on the droplet's surface. The capillary waves may be strong enough to induce ejection of a satellite droplet from the primary one. In this study, we show that the size of the satellite droplet and the ejection time are not only dependent on the contact-line velocity, which directly relates to the applied voltage enabling the electrowetting effect, but also affected by the ejection dynamics. We derive a theoretical model of the criteria for droplet ejection and experimentally verify the proposed criteria for wide ranges of viscosity, droplet size and the applied voltage.