Influence of Surface Wettability on Discharges from Water Drops in Electric Fields

Abstract

It is known that electrified droplets deform and may become unstable when the electric field they are exposed to reaches a certain critical value. These instabilities are accompanied by electric discharges due to the local enhancement of the electric field caused by the deformed droplets.Here we report and highlight an interesting aspect of the behavior of unstable water droplets and discharge generation: by implementing wettability engineering, we can manipulate these discharges. We demonstrate that wettability strongly influences the shape of a droplet that is exposed to an electric field. The difference in shape is directly related to differences in the critical value of the applied electric field at which inception of discharge occurs. Using theoretical models, we can predict and sufficiently support our observations. Thus, by tailoring the wettability of the surface, we can control droplet's behavior from expediting the discharge inception to completely restricting it.

Droplet Self-Propulsion on Superhydrophobic Microtracks

“…34−36 The clustered nanoneedles are then coated with a self-assembled monolayer (SAM), i.e., a perfluorodecanenthiol that reduces the surface energy of the substrate and renders it superhydrophobic (see Experimental Section). 35,36 Typical advancing and receding contact angles of such a nanostructured surface are θ rec = 162.0°± 1.6°and θ adv = 164.7°± 1.0°, respectively, resulting in a contact angle hysteresis of Δθ = θ adv − θ rec = 2.7 ± 1.9°. A droplet placed on such a surface forms a series of elongated diverging menisci at its underside, as shown schematically in Figure 1c.…”

“…This has a beneficial effect because it generates an upward capillary force aiding the superhydrophobic state of the droplet. To minimize the adhesion forces and facilitate self-propulsion, we render the surface superhydrophobic by adding a second-level roughness to the tracks with the help of a cluster of Cu­(OH) 2 nanoneedles, with a thickness of ∼200 nm (see Figure b). − The clustered nanoneedles are then coated with a self-assembled monolayer (SAM), i . e ., a perfluorodecanenthiol that reduces the surface energy of the substrate and renders it superhydrophobic (see Experimental Section).…”

“…e ., a perfluorodecanenthiol that reduces the surface energy of the substrate and renders it superhydrophobic (see Experimental Section). , Typical advancing and receding contact angles of such a nanostructured surface are θ rec = 162.0° ± 1.6° and θ adv = 164.7° ± 1.0°, respectively, resulting in a contact angle hysteresis of Δ θ = θ adv – θ rec = 2.7 ± 1.9°.…”

“…Next, the microstructured copper sample was cleaned using ultrasonication by dipping it sequentially into baths of hydrochloric acid, acetone, isopropanol, and water. Then the sample was immersed in an aqueous solution of 77.5 mM sodium hydroxide (Merck) and 3.1 mM ammonium persulfate (Merck) for 25 min followed by immersion in an aqueous solution of 2.5 M sodium hydroxide and 0.1 M ammonium persulfate for 7.5 min. ,, After that, the sample is cleaned with water and dried using nitrogen. The outcome of this process is the formation of clustered copper hydroxide nanoneedles superimposed on the microtracks, resulting in a surface that has a hierarchical micro/nanotexture.…”

Electric Field Mediated Contact Time Reduction of Impacting Drops on Cu(OH)2 Nanoneedle Clusters: Limitations and Implications for Anti-Icing and Pathogen-Containment Applications

“…To support our proposed strategy, we conducted simulations using COMSOL Multiphysics . It should be noted that the behavior of sessile drops inside constant and alternating background electric fields has been explored thoroughly experimentally , and computationally. − However, in addition to the residence time reduction and its significant implications, the general topic of drop impact in electric fields has not been studied widely , in the literature. In particular, existing works investigate the shape evolution of an impacting drop in an electric field.…”