Issue 47, 2021

Reversible electrowetting transitions on superhydrophobic surfaces

Abstract

An electric field applied across the interface has been shown to enable transitions from the Cassie to the Wenzel state on superhydrophobic surfaces with miniature corrugations. Molecular dynamics (MD) simulations manifest the possibility of reversible cycling between the two states when narrow surface wells support spontaneous expulsion of water in the absence of the field. With approximately 1 nm sized wells between the surface asperities, the response times to changes in the electric field are of O(0.1) ns, allowing up to GHz frequency of the cycle. Because of the orientation preferences of interfacial water in contact with the solid, the phenomenon depends on the polarity of the field normal to the interface. The threshold field strength for the Cassie-to-Wenzel transition is significantly lower for the field pointing from the aqueous phase to the surface; however, once in the Wenzel state, the opposite field direction secures tighter filling of the wells. Considerable hysteresis revealed by the delayed water retraction at decreasing field strength indicates the presence of moderate kinetic barriers to expulsion. Known to scale approximately with the square of the length scale of the corrugations, these barriers preclude the use of increased corrugation sizes while the reduction of the well diameter necessitates stronger electric fields. Field-controlled Cassie-to-Wenzel transitions are therefore optimized by using superhydrophobic surfaces with nanosized corrugations. Abrupt changes indicate a high degree of cooperativity reflecting the correlations between the wetting states of interconnected wells on the textured surface.

Graphical abstract: Reversible electrowetting transitions on superhydrophobic surfaces

Associated articles

Article information

Article type
Paper
Submitted
15 Sep 2021
Accepted
05 Nov 2021
First published
05 Nov 2021
This article is Open Access
Creative Commons BY-NC license

Phys. Chem. Chem. Phys., 2021,23, 27005-27013

Reversible electrowetting transitions on superhydrophobic surfaces

D. Vanzo, A. Luzar and D. Bratko, Phys. Chem. Chem. Phys., 2021, 23, 27005 DOI: 10.1039/D1CP04220C

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