Lubrication effects on droplet manipulation by electrowetting-on-dielectric (EWOD)

TL;DR

This paper investigates how oil-infused electrowetting-on-dielectric (EWOD) surfaces influence droplet movement, revealing a quadratic relationship between voltage and velocity and demonstrating significantly increased droplet speeds due to lubrication effects.

Contribution

It introduces a physical model for droplet velocity on oil-infused EWOD surfaces and compares lubrication effects with other liquid-infused surfaces, showing enhanced droplet speeds.

Findings

Droplet velocity scales with the square of the electric field (E^2).

Achieved droplet velocity of 1 mm/s at 15 V.

Velocity is ten times higher than on porous-structure liquid-infused surfaces.

Abstract

Electrowetting has a potential to realize stand-alone point-of-care (POC) devices. Here we report droplet-migration characteristics on oil-infused electrowetting-on-dielectric (EWOD) substrates. We prepare sparse micropillars to retain the oil layer in order to exploit the layer as a lubricating film. A physical model of the droplet velocity is developed, and effects of the lubrication, the oil viscosity, the droplet volume, and the thickness of solid and liquid dielectric layers are discussed. It is found that the droplet velocity is scaled as square of E, which differs from a relationship of cube of E for droplets sliding down on liquid-infused surfaces by gravity. Furthermore, our device achieves droplet velocity of 1 mm/s at the applied voltage of 15 V. The velocity is approximately tenfold as high as the same condition (applied voltage and oil viscosity) on porous-structure-based liquid-infused surfaces. The achieved high velocity is explained by a lubrication-flow effect.