Abstract

When a voltage difference is applied between a conducting liquid and a conducting (solid) electrode, the liquid is observed to spread on the solid. This phenomenon, generally referred to as electrowetting, underpins a number of interfacial phenomena of interest in applications that range from droplet microfluidics to optics. Here, we present a lattice-Boltzmann method that can simulate the coupled hydrodynamics and electrostatics equations of motion of a two-phase fluid as a means to model the electrowetting phenomena. Our method has the advantage of modeling the electrostatic fields within the lattice-Boltzmann algorithm itself, eliminating the need for a hybrid method. We validate our method by reproducing the static equilibrium configuration of a droplet subject to an applied voltage and show that the apparent contact angle of the drop depends on the voltage following the Young-Lippmann equation up to contact angles of ≈50°. At higher voltages, we observe a saturation of the contact angle caused by the competition between electric and capillary stresses, similar to previous experimental observations. We also study the stability of a dielectric film trapped between a conducting fluid and a solid electrode and find a good agreement with analytical predictions based on lubrication theory. Finally, we investigate the film dynamics at long times and report observations of film breakup and entrapment similar to previously reported experimental results.

Highlights

  • Electrowetting refers to the spreading of an electrically conducting liquid on a solid electrode when a voltage difference is applied between the two.[1]

  • Because of its ability to control the interaction of liquids with solid surfaces, electrowetting has triggered a number of applications, such as droplet-based microfluidic devices,[2−5] droplet actuation[6,7] and mixing,[8−11] deformable optical apertures[12] and lenses,[13,14] and electronic paper displays.[15−18] Broadly speaking, there are two types of electrowetting setups: electrowetting on conductor (EWOC), in which the conductive liquid is in direct contact with the solid electrode,[19] and the more popular electrowetting on dielectric (EWOD), in which direct contact is removed by coating the electrode with a dielectric layer.[20−22]

  • We validate the lattice-Boltzmann algorithm by studying the electrowetting-driven spreading of a droplet in an EWOD setup

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Summary

Introduction

Electrowetting refers to the spreading of an electrically conducting liquid on a solid electrode when a voltage difference is applied between the two.[1]. To model the effect of the electrostatic potential field, it suffices to introduce an algorithm that solves Laplace’s equation in the dielectric, while keeping the potential to a constant value in the conductor.

Results
Conclusion

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