Experimental and theoretical study of electrowetting dynamics on slippery lubricant-infused porous surfaces

Abstract

The droplet electrowetting dynamic behaviors on slippery lubricant-infused porous surfaces (SLIPS) remain elusive because the soft liquid-liquid interface nature is much different from solid dielectric hydrophobic surfaces. To understand the dynamic process, the impact of the voltage applied, the oil thickness, and viscosity on dynamic electrowetting behavior was experimentally studied, respectively. Meanwhile, a numerical dynamic model was also developed for the quantitative interpretation of the droplet dynamic spreading process on SLIPS. It is found the droplet always spreads smoothly to the equilibrium state without overshooting on the SLIPS. The droplet is always over-damped with the increase of applied voltage, the settling time is proportional to the 0.9th power of the electrowetting number. Then, by changing the silicone oil viscosity, it is found the viscous dissipation of the oil-water interface becomes dominant, causing the droplet to spread slowly. By fitting the theoretical models to experimental results, it is found the friction coefficient is nearly proportional to 1/6th power of oil viscosity and rarely influenced by applied voltage and oil thickness. Finally, it is found both the initial oil thickness and the high wetting ridge have a minor influence on the electrowetting dynamic spreading. The relationship between the actual oil layer thickness and the initial oil layer thickness was estimated. This study will provide helpful information and theory support for electrowetting-on-dielectric device design, lab on a chip, and other potential applications on SLIPS.