Electrical actuation of liquid droplets on smooth and artificially microstructured surfaces

Electrically induced actuation of liquid droplet motion has significant applications in the field of MEMS and lab-on-a-chip devices. This dissertation presents results on the fundamentals governing the electrical actuation of liquid droplets on smooth and artificially microstructured surfaces.;A physics-based analytical model is formulated to predict transient EW-induced motion of an electrically conducting droplet between flat plates. A generic modeling framework for predicting the actuation force on a generic liquid droplet (electrically conducting or insulating) under DC or AC actuation is also developed. It is seen that the electrical actuation force on a droplet depends on the electrical properties of the liquid and the dielectric layer, the dielectric layer thickness, plate spacing and the frequency of the AC actuation voltage. Detailed experiments which involve the measurement of droplet velocities are conducted to benchmark the predictions of the electromechanical model.;The present work also studies droplet morphology and state transitions on artificially microstructured electrowetted surfaces. An analytical model which predicts the EW-induced Cassie-Wenzel transition on such surfaces is developed. Extensive experiments to study the EW-induced transition and quantify the reversibility of the transition are presented. It is seen that the presence of an energy barrier and dissipative forces hinder the reversibility of the Cassie-Wenzel transition. The dissertation also presents two novel concepts for enhanced control of droplet morphology on artificially microstructured surfaces.