Impact of Gravitational Force on Dynamic Contact Angle and Velocity of Microdroplets on Hydrophobic Surfaces in Digital Microfluidics

Digital microfluidics (DMF) is a novel technology that deals with the movement or transportation of microscale fluid on electrodes of small cross-sectional areas. The innovative system provides flexibility in terms of the movement of discrete droplets. Despite the vast knowledge of droplet dynamics and droplet formation in simple cases, it is important to know about droplet behavior on an inclined surface in addition to electric forces. Hence, this study investigates the dynamic of contact angle and velocity of microdroplets on hydrophobic surfaces angled against gravity in a digital microfluidics chip. The microdroplets are experimentally and numerically investigated to understand the changes in dynamic contact angles and velocity. In addition, external forces like the surface tension and electric forces affecting the droplet behavior have also been included in the study. Our study relates the interdependence between the angle of chip tilt, the hydrophobic/hydrophilic characteristic of the surface, and external forces acting on droplets of DMF systems. This contributes to enhancing the knowledge of droplet control in practically significant microfluidic processes.