Numerical investigation of micro-droplets mixing in electrowetting-on-dielectric digital microfluidics: The merging process and frequency response

Abstract

In this study, we numerically investigate the mixing of two sessile micro-droplets in open electrowetting-on-dielectric (EWOD) digital microfluidics. The mixing process is composed of the merging and the subsequent oscillation process achieved by applying alternating voltage (AC voltage) to the droplet with desired frequency and amplitude. The numerical results show excellent agreement with previous numerical and experimental studies. The focus of this study is probing into the effects of the merging process on the subsequent AC voltage-actuated oscillation of the droplet. It is observed that the merging process breaks the azimuthal symmetry of the droplet and, hence, introduces the sectoral mode to the subsequent AC voltage-actuated oscillation. The frequency dependence of the enhancement and dissipation of the sectoral oscillation is quantitatively investigated. Furthermore, the sectoral oscillation inherited from the merging process is confirmed to have little impact on the zonal oscillation of the droplet. The oscillation-based mixing enhancement of the droplet is numerically verified.