Integrating electrowetting into micromanipulation of liquid droplets

Electrowetting is proposed as a new principle for micromanipulation of a liquid droplet. A conical gripper was used to pick up a droplet and release it onto a substrate by controlling the wetting property between the droplet and the substrate using electrowetting. The rupture process of the liquid bridge between the gripper and the substrate as formed during the pick-up and release stages is studied using a precise numerical method and the arc approximation. The efficiency of micromanipulation is quantified using a term volumetric distribution ratio, which is the volume of the droplet retained by the substrate divided by the whole volume of the liquid droplet during a rupture process, for different combinations of contact angles between the liquid and the gripper or the substrate and the aperture of the conical gripper. Based on the theoretical analysis, an optimized micromanipulation process is suggested which could achieve 100% efficiency by carefully choosing the parameters mentioned above. Preliminary experiments are performed with a commercially available AFM probe to demonstrate this concept. The experimental results are compared with the theoretical prediction proposed here.