Electrowetting channel transports droplets with and without gravity

By applying an electric field to a droplet-covered surface, electrowetting can alter the interfacial tension and reduce the contact angle of the droplet. This creates a force imbalance that causes the droplet to move, which can be exploited to induce bulk liquid motion.

Huo et al. designed a numerical model to examine the fundamental process of electrowetting and clarified the dynamics of directional fluid transport.

“Directional fluid transport is used to transport fluid in a desired direction and in an effective way,” said author Qinggong Wang. “It is very important for fluid management, propellant filling, and heat transfer enhancement both on Earth and in microgravity.”

The model is based on the phase field method. The team introduced a dynamic contact angle by including three-phase contact line friction and pinning force.

They observed three stages of droplet deformation and motion. In the first, the droplet stretches out as the front moves while the tail end remains static. In the second stage, the tail end begins to move, increasing the contact angle at the back of the droplet until it reaches a steady state. Finally, the whole droplet keeps a constant shape and speed as it slides on the substrate.

“We demonstrate the dynamics of droplet transport in a narrow channel by covering a wide range of operating conditions,” said Wang. “We explain the effect of gravity on fluid transport by electrowetting and show the anti-gravity properties of the device.”

The researchers plan to fabricate the electrowetting channel to study the fluid transport experimentally on Earth and in a drop tower.

Source: “The dynamics of directional transport of a droplet in programmable electrowetting channel,” by Xiaozhi Huo, Long Li, Yang Yang, Xuefeng Liu, Qiang Yu, and Qinggong Wang, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0139965 .