Improved Modeling of Droplet Motion in Open-Format Digital Microfluidic Devices

Abstract

Electrowetting is an electrokinetic effect whereby an applied electric field induces changes in the measured contact angle at a fluid-surface contact line. On hydrophobic, dielectric electrode surfaces, this effect generates droplet motion termed “electrowetting on dielectric” or EWOD. Applications of this phenomenon range from lab-on-a-chip to liquid lenses capable of altering their topology and focus within milliseconds. Electrowetting or EWOD theoretical models quantifying this effect fall into two paradigms: the Young-Lippman and the electromechanical theories. In this work, both paradigms were simulated to predict the velocity of a water droplet moving over an array of electrodes. Results were compared to experimental observations of measured velocities for two dielectric films: ETFE and household cling film. Theoretical model parameters, namely the length scale of the Maxwell force on the droplet, were also determined to align simulation and experiment. The results reveal the trend of droplet velocity in relation to applied voltage, and recapitulate the relationship between the two models.