Molecular Investigation of the Actuation of Electrowetted Nanodroplets

It is well known that the wettability of a droplet on a solid substrate can be modified by the application of an electric field. The phenomenon of electrowetting along with the associated physics of droplet shape change and dynamics has traditionally been studied at the micro-scale leading to exciting applications. The present work is undertaken to explore the physics of electrowetting actuation of droplet movement at the molecular level. Molecular simulations are performed to obtain the dynamic spreading of the droplet under the action of a radially symmetric electric field on a silica substrate. The dynamic behavior of the contact diameter is found to be qualitatively similar to that observed at the laboratory scale. Further simulations of droplet actuation across an array of electrodes illustrated the dynamics of the center of mass, which is then used to estimate the contact line friction and compared with the predictions from a reduced-order model. A scaling analysis is used to probe the physics of the problem correlating the contact line friction coefficient and the droplet velocity after actuation. The results and understanding elicited from the fundamental approach have the potential to guide the development of quick and precise control of nano-sized droplets and may prove to be pivotal in the development of future nanofluidic systems, nanomanufacturing methodologies, and high-resolution optoelectronic devices.