Abstract
Superhydrophobic surfaces have aroused great interest for being promising candidates in applications such as self-cleaning, anti-icing, and corrosion resistance. However, most of the superhydrophobic surfaces lose their anti-wettability in low surface temperature and high humidity. The loss of superhydrophobicity by condensed liquid is a very common practical incident, yet to be understood properly. Here we report the wettability of the superhydrophobic nanoporous surfaces in condensation and freezing environments. Various structured surfaces fabricated with carbon nanotubes (CNT) and coated by an ultrathin, conformal, and low surface energy layer of poly (1H,1H,2H,2H-perfluorodecylacrylate) (pPFDA) are exploited in humid conditions. Droplet impact dynamics, condensate characteristics, and freezing time delays are investigated on the CNT micropillars with various geometries along with the CNT forest and two commercially available anti-wetting coatings, NeverWet and WX2100. Nanoporous microstructured CNT pillars with the favorable topological configuration demonstrated complete droplet bouncing, significant freezing delays, and considerable durability during several icing/de-icing cycles. This study provides an understanding on the preferable geometry of the highly porous CNT micropillars for retaining hydrophobicity and preventing ice formation, which is of practical importance for the rational development of anti-wetting surfaces and their applications in low temperatures and humid conditions.
Highlights
IntroductionSuperhydrophobic surfaces have shown excellent anti-wetting properties identified by high water contact angle (WCA) and very small WCA hysteresis (difference between advancing and receding WCA) [13]
We investigated the characteristics of condensation forming on the various fabricated pPFDA-coated nanoporous microstructured surfaces and commercially available hydrophobic coatings
The carbon nanotubes (CNT) micropillars retained their hydrophobicity even after considerable amount of time in condensation environments, having their air pockets not filled by the condensate drops
Summary
Superhydrophobic surfaces have shown excellent anti-wetting properties identified by high water contact angle (WCA) and very small WCA hysteresis (difference between advancing and receding WCA) [13]. Some of these surfaces typically have very low surface energy with micro-scale, nano-scale, and/or hierarchical features that enable entrapping a thin air layer between them and the droplet [14,15,16,17]. Some other anti-icing performances exhibited by the superhydrophobic surfaces include lowering ice adhesion strength, repelling freezing rain droplets, and delaying frost formation [13,24,25,26,27,28,29,30]. Under harsh environmental conditions like low temperatures and high humidity, these surfaces lose their superhydrophobicity and fail to exhibit those anti-icing features [31,32,33,34]
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