Research On Contact Angle Hysteresis In Electrowetting On Dielectric

Contact angle hysteresis(CAH) is one of the significant physical phenomena in electrowetting on dielectric(EWOD). It is omnipresent in nature and also plays a crucial role in various industrial processes.With the theoretical and experimental study on EWOD, more and more researchers pay close attention to contact angle hysteresis. However,many issues of how the CAH in EWOD formed and the model of CAH in EWOD have not been resolved.This paper describes the theory of interface, basic equations of EWOD, the relevant knowledge of contact angle hysteresis, and a variety of contact angle models. Many theoretical and experimental studies have been done about the origin of CAH in EWOD in electrowetting evolution. Firstly, we analyse the influence of various frictions including static friction, dynamic friction and viscous friction around three phase contact line on the CAH. A theoretical model is proposed to characterize electrowetting evolution on substrates with CAH, and the relationship between apparent contact angle, potential and some other parameters is quantified. Secondly, we test and analysis the kinetic process of EWOD. By analyzing the influences of frequency on CAH in EWOD, the results indicate that our theory based on energy balance succeed in describing the electrowetting response of potential with significant contact angle hysteresis. The CAH in EWOD increases with the increased voltage and climbs up to the maximum when voltage is increased to a point, and then decreases to zero with the increase of voltage. Finally, the effects of direct current(DC) and alternating current(AC) on contact angle hysteresis are discussed. It shows that the contact angle hysteresis is small with AC voltage.