Influence of polarization on contact angle saturation during electrowetting

Abstract

Electrowetting is widely used to manipulate liquids on a dielectric surface by changing the wettability of the solid-liquid interface using an externally applied electric field. While the contact angle can be adequately predicted at low fields using Lippmann's model, there is a large disagreement with experimental behavior at high fields, where the contact angle saturates. Previous attempts to explain this saturation effect (by considering a range of different mechanisms) have led to models that are applicable only to limited field ranges. Here, we use a model for the solid-liquid interfacial surface energy (based on a dipole-dipole interaction) to describe electrowetting and find that this explains the contact angle change at both low (continuous change) and high (saturation) fields. The model is compared with measured contact angle changes for both water and ethylene glycol liquids, with good agreement over the whole field range.