Electrowetting hysteresis on a deformable dielectric film.

Electrowetting on dielectric (EWOD) involves actuating droplets through electrical stimulus while the droplets lie on a dielectric layer that covers the electrode. In order to activate the droplet, a higher threshold voltage is required due to electrowetting hysteresis. The effect of a deformable dielectric layer and its thickness on electrowetting hysteresis has not been studied. We demonstrate in this work that electrowetting hysteresis increases with decreasing elasticity of the dielectric layer. This is attributed to the formation of wetting ridges along the three-phase contact line and relies on electro-elastic capillary interactions. Furthermore, we demonstrate that the thickness of the dielectric film can affect electrowetting hysteresis on soft materials. In addition, we present a unique mechanism of electrowetting hysteresis reduction on soft solids by the addition of a minute amount of anionic surfactant (sodium dodecyl sulfate, SDS) to the liquid. We also demonstrate that the voltage cycle affects the electrowetting hysteresis of sessile drops on a soft dielectric layer. Dielectric layer elasticity can be used in various engineering applications, such as optofluidic displays, liquid lenses, lab-on-a-chip devices, and energy harvesting systems.