Drop impact onto polarized dielectric surface for controlled coating

Abstract

Control of surface wettability by means of electrowetting-on-dielectric (EWOD) is among the most effective methods of active enhancement of surface wettability. Here, electrohydrodynamics of drop impact onto a dielectric surface with electrodes embedded in the dielectric (or aligned and attached to it) is experimentally investigated. Drop impact of different liquids (water, n-butanol, and motor oil) onto different substrates (stretched Teflon, parafilm, and polypropylene) is studied. Water drop impact onto stretched Teflon (the only Teflon which revealed significant electrowetting) and un-stretched parafilm surfaces is studied in detail. The results for water drop impact indicate that drop spreading on such non-wettable surfaces can be significantly enhanced by the electric field application. In particular, water drop rebound can be suppressed by the electric force. Furthermore, impact dynamics and spreading of hydrocarbon liquids with electric field are explored. Partial suppression of splash phenomena was also observed with the application of the electric field in addition to enhancement of spreading. In addition, the experimental results for water drops are compared with the Cahn−Hilliard−Navier−Stokes (CHNS) simulations for static contact angles and drop impact dynamics, and the results are in close agreement for water drops. This study demonstrates that electrowetting-on-dielectric holds great promise for coating and spraying technologies.