title: Dynamic Response in Nanoelectrowetting on a Dielectric.
abstract: Droplet spreading at an applied voltage underlies the function of tunable optical devices including adjustable lenses and matrix display elements. Faster response and the enhanced resolution motivate research toward miniaturization of these devices to nanoscale dimensions. The response of an aqueous nanodroplet to an applied field can differ significantly from macroscopic predictions. Understanding these differences requires characterization at the molecular level. We describe the equilibrium and nonequilibrium molecular dynamics simulations of nanosized aqueous droplets on a hydrophobic surface with the embedded concentric electrodes. Constant electrode potential is enforced by a rigorous account of the metal polarization. We demonstrate that the reduction of the equilibrium contact angle is commensurate to, and adjusts reversibly with, the voltage change. For a droplet with O(10) nm diameter, a typical response time to the imposition of the field is of O(10(2)) ps. Drop relaxation is about twice as fast when the field is switched off. The friction coefficient obtained from the rate of the drop relaxation on the nonuniform surface, decreases when the droplet approaches equilibrium from either direction, that is, by spreading or receding. The strong dependence of the friction on the surface hydrophilicity points to the dominance of the liquid-surface friction at the drop's perimeter as described in the molecular kinetic theory. This approach enables correct predictions of trends in dynamic responses associated with varied voltage or substrate material.
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors.forename: Jyoti Roy
authors.initials: JR
authors.lastname: Choudhuri
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors.forename: Davide
authors.initials: D
authors.lastname: Vanzo
authors.affiliation: Department of Material Science, Oxford University , Park Road, Oxford OX1 3PH, United Kingdom.
authors.forename: Paul Anthony
authors.initials: PA
authors.lastname: Madden
authors.affiliation: Sorbonne Universités, UPMC Université Paris 06, CNRS, UMR 8234 PHENIX , 75005 Paris, France.|Maison de la Simulation, CEA, CNRS, Université Paris-Sud, UVSQ, Université Paris-Saclay , F-91191 Gif-sur-Yvette, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Salanne
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors.forename: Dusan
authors.initials: D
authors.lastname: Bratko
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
authors.forename: Alenka
authors.initials: A
authors.lastname: Luzar
keywords: dielectric; dynamic electrowetting; molecular dynamics; nanopixel; nanoscale