Dynamics of droplets driven by electrowetting

TL;DR

This paper develops a theoretical model using Onsager variational principle to describe the complex dynamics of droplets under electrowetting, providing insights into their spreading and retraction behaviors across different regimes.

Contribution

It introduces a comprehensive theoretical framework for electrowetting droplet dynamics, capturing both overdamped and underdamped regimes, and elucidates the influence of various parameters on transient behaviors.

Findings

Droplet dynamics can be modeled effectively in the overdamped regime.

Transient timescales are independent of viscosity, size, and voltage.

The model explains spreading and retraction behaviors in electrowetting.

Abstract

Even though electrowetting-on-dielectric (EWOD) is a useful strategy in a wide array of biological and engineering processes with numerous droplet-manipulation applications, there is still a lack of complete theoretical interpretation on the dynamics of electrowetting. In this paper, we present an effective theoretical model and use Onsager variational principle to successfully derive the governing equations of non-equilibrium electrowetting dynamics for a droplet in both overdamped and underdamped regimes. It is found that the spreading and retraction dynamics of a droplet on EWOD substrates can be fairly well captured in the overdamped regime. By varying liquid viscosity, droplet size, and applied voltage, we confirm that the transient dynamics of EW can be characterized by a timescale independent of liquid viscosity, droplet size and applied voltage. Our model provides a complete fundamental explanation of EW-driven spreading dynamics, which is important for a wide range of applications, from self-cleaning to novel optical and digital microfluidic devices.