Dual dimensional nanostructures with highly durable non-wetting properties under dynamic and underwater conditions

Abstract

Non-wetting states with high durability under both dynamic and underwater conditions are very desirable for practical applications of superhydrophobic surfaces in various fields. Despite increasing demands for this dual stability of non-wetting surfaces, studies investigating both the impact dynamics and underwater stability are very rare. In the current study, we performed water droplet impact dynamics and underwater stability studies using ZnO/Si hierarchical nanostructures (HNs) as a model system. The effects of the surface structure on the non-wetting states under dynamic conditions were first studied by comparing various surface structures, such as ZnO nanowires (NWs), Si microposts (MPs), ZnO/Si HNs with controlled MP interspacings, and lotus leaf (LL). The growth of ZnO NWs on Si MPs drastically improves the non-wetting properties of Si MPs under dynamic conditions. The transition of wetting states from the Cassie-Baxter state to the Wenzel state occurs on ZnO/Si HNs as the impact velocity increases. Measurement of the critical We number during transition enables us to determine the important parameters of wetting pressure using a simple model. Moreover, compared to Si MPs, ZnO NWs, and LL, our ZnO/Si HNs exhibit dramatically increased air pocket lifetimes under underwater conditions, which is due to the enhanced capillary pressure originating from the dual dimensional hierarchical structure. Our study indicates that optimally designed hierarchical surfaces have remarkably high durability non-wetting states under both dynamic and underwater conditions, expanding the potential application of non-wetting surfaces.

Recent Progress in Preparation and Anti-Icing Applications of Superhydrophobic Coatings

“…The results revealed that rebound characteristics were governed by the energy dissipation during the impact and wetting transition within the structure. Yong et al performed water droplet impact dynamics and underwater stability studies using ZnO/Si hierarchical nanostructures (HNs) as a model system [136] in Figure 14. Results indicated that decrease in the Weber (We) number could induce the conversion of the wetting state to the anti-wetting state because of the decrease in relative magnitude of wetting force compared to the surface energy.…”

“…Snapshots of the impact dynamics of water droplets showing the transition between wetting/anti-wetting states at a critical We number: (a) ZnO/Si HNs with 50 µm spacing distance, showing a transition from the wetting state to the anti-wetting state at We = 9; (b) ZnO/Si HNs with 100 µm spacing distance, showing a transition from the wetting state to the anti-wetting state at We = 1.5; and (c) Schematic representation describing the transition from the wetting state to the anti-wetting state. (Adapted from[136] with permission; Copyright 2017 RSC).…”

One‐step fabrication of wear‐resistant superhydrophobic coating based on aminosilane‐functionalized diatomaceous earth

“…As shown in Figure 13(a), a mirror-like layer is clearly observed on the coating surface after immersion, which is owing to the existence of air pockets at the interface between the water and the solid surface. 56,57 Usually, the air pockets are unstable and will gradually be replaced by water. The disappearance of the air pockets will cause the area of the shiny layer to reduce, indicating the decrease of hydrophobicity.…”

What Can Probing Liquid–Air Menisci Inside Nanopores Teach Us About Macroscopic Wetting Phenomena?

“…Under certain circumstances, disturbances induced by surface vibration or droplet evaporation, condensation, or impingement can cause the collapse of the otherwise stable liquid–air interface beneath the droplet, resulting in some transient intermediate states − or the fully filled Wenzel state . The transition can take from a few seconds to more than a week and can be reversible, depending on the properties of the surface and the liquid. ,,, Investigating the stability criteria of the Cassie–Baxter state under various static and dynamic conditions is of fundamental as well as practical significance.…”

“…14 The transition can take from a few seconds to more than a week and can be reversible, 13 depending on the properties of the surface and the liquid. 12,13,15,16 Investigating the stability criteria of the Cassie−Baxter state under various static and dynamic conditions is of fundamental as well as practical significance.…”