Molecular Dynamics Insights into Electric Field and Medium Effects on Electrowetting-on-Dielectric Droplet Spreading

Microfluidic device performance relies on precise control of droplet dynamics in electrowetting-on-dielectric (EWOD) systems, yet the atomic-scale mechanisms by which electric field characteristics and ambient media regulate droplet behavior remain poorly defined. In this study, we combine molecular dynamics (MD) simulations with experimental EWOD techniques to investigate the impacts of electric field type (AC vs DC) and ambient medium on droplet behavior. The goal is to elucidate the underlying mechanisms and provide atomic-level guidance for microfluidic system optimization. Our results demonstrate that DC actuation enhances wetting efficacy by promoting structural ordering and increasing liquid-substrate hydrogen bonding interactions; however, this enhanced structural ordering also leads to consistently higher contact angle hysteresis and saturation. Conversely, AC fields mitigate contact angle hysteresis and improve actuation reversibility by limiting molecular adsorption at the liquid-solid interface. The dodecane ambient medium significantly outperforms vacuum/air in boosting EWOD efficiency, acting as a molecular lubricating layer at the three-phase contact line to minimize pinning effects, thereby reducing contact angle hysteresis and improving the reversibility of wetting dynamics. This work elucidates the atomic-scale mechanisms underlying EWOD-driven droplet behavior, offering fundamental insights that enable the rational design and optimization of high-performance microfluidic systems.