Numerical Study of Electrowetting and Emulsification of Sessile Droplets in Viscous Fluid

Electrowetting on dielectric (EWOD) is widely used to control droplet dynamics via applied voltage. In its study, negligible surrounding fluid shear and electrohydrodynamic coupling are often assumed. However, this assumption might not hold when droplets are immersed in viscous fluid, where interfacial stresses and fluid viscosity have significant influence over droplet motion. In this study, we numerically investigate the wettability dynamics of a water droplet in an oil environment under various voltages. The model accounts for Maxwell stress contributions and shear forces generated by the surrounding oil, as well as the influence of oil viscosity and adding surfactant on the evolution of the contact angle. The model is first validated by numerically simulating a classical electrowetting problem with a sessile droplet under an electric field. Then, the model is further developed to simulate emulsification, where one liquid droplet is dispersed into smaller droplets within another immiscible liquid, under certain voltage and other preferable fluid conditions.