Reversible electrowetting transitions on superhydrophobic surfaces

Authors

D. Vanzo
A. Luzar
D. Bratko, Virginia Commonwealth UniversityFollow

Document Type

Article

Original Publication Date

2021

Journal/Book/Conference Title

Physical Chemistry Chemical Physics

Volume

23

First Page

27005

DOI of Original Publication

https://doi.org/10.1039/D1CP04220C

Comments

This is the author's manuscript version of the article published in Phys. Chem. Chem. Phys., 2021,23, 27005-27013. DOI: https://doi.org/10.1039/D1CP04220C

Date of Submission

May 2022

Abstract

Electric field applied across the interface has been shown to enable transitions from Cassie to 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, response times to changes of electric field are of O(0.1) ns, allowing up to GHz frequency of the cycle. Because of 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 wetting states of interconnected wells on the textured surface.

Is Part Of

VCU Chemistry Publications