Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

Abstract

interest has focused on utilizing the lowadhesivity nature of superhydrophobic surfaces for the rapid removal of condensate microdrops, as this has significance in fundamental research and technological innovation. Example applications are the enhancement of condensation heat transfer for high-efficiency thermal management and energy utilization, [20][21][22][23][24][25] energy-effective antifreezing for airconditioner heat exchangers and aircraft wings, [26][27][28] and electrostatic energy harvesting. [29] In general, condensate drops on typical flat hydrophobic surfaces are only shed off under gravity when their sizes are comparable to the capillary length (≈2.7 mm for water), [30] which creates undesirable effects such as large thermal resistance [20][21][22][23][24][25] and the freezing of subcooled drops. [26][27][28] Clearly, a great challenge is the timely removal of condensate drops at the microscale where the gravitational effect does not work. The latest research has indicated that these small-scale condensate microdrops may self-remove via mutual coalescence as long as the coalescence-released excess surface energy is larger than the interface adhesion-induced energy dissipation. [31] Much effort has been devoted to exploring the utilization of knowledge of bionic low-adhesivity superhydrophobicity to develop innovative condensate microdrop self-propelling (CMDSP) surfaces. Different from traditional superhydrophobic surfaces, which are characterized by the bouncing or rolling off of deposited millimeter-size large drops, [32,33] CMDSP surfaces support the self-removal capability of smallscale condensate microdrops. It has been reported that classical superhydrophobic lotus leaves (Figure 1a), [34][35][36][37] as well as artificial surfaces consisting of hierarchical micro-and nanostructures, [38] one-tier microstructures, [39][40][41][42][43] or nanostructures [44,45] with larger characteristic interspaces, present a low-adhesivity property to the deposited water macrodrops, but become highly adhesive to condensed microdrops (Figure 1b). This is because moisture easily penetrates the microscale valleys or cavities. Clearly, superhydrophobic surfaces with irrationally designed surface structures can enhance the solid-liquid interfacial adhesion instead of promoting the rapid removal of condensed drops. Accordingly, it is still a challenge to design and fabricate very effective low-adhesivity superhydrophobic surfaces with the self-removal ability of condensate microdrops. Recently, there has been a large breakthrough in understanding the mechanism and construction rules of bionic CMDSP surfaces, leading to the exploration of fabrication methods for the surface functionalization of widely used metal materials and the Bionic condensate microdrop self-propelling (CMDSP) surfaces are attracting increased attention as novel, low-adhesivity superhydrophobic surfaces due to their value in fundamental research and technological innovation, e.g., for enhancing heat transfer, energy-effective antifreezing, and...

Tunable Wetting Patterns on Superhydrophilic/Superhydrophobic Hybrid Surfaces for Enhanced Dew‐Harvesting Efficacy

“…This may be because under the dew conditions, the water‐harvesting performance is determined by both the water capturing rate and the water removal efficiency, which require the surface to exhibit different wettability for each contribution; wettable surfaces favor droplet nucleation, whereas SHPo surfaces favor droplet removal. Since the droplet nucleation barrier on the SHPo surface is higher than that on the SHPi surface, the low condensation rate limits the overall water collection efficiency; additionally, if the droplets depart from the SHPo surface via coalescence‐induced jumping, the departing droplets would be evaporated in the air, causing a larger loss of water collection, despite fast droplet departure frequency on the SHPo surface …”

Water‐Based Robust Transparent Superamphiphobic Coatings for Resistance to Condensation, Frosting, Icing, and Fouling

“…Inspired by nature, [ 4–7 ] superhydrophobic surfaces with extreme repellency to water have attracted significant interest, owing to their potential applications in anti‐condensation, anti‐frosting, anti‐icing, anti‐fogging, and self‐cleaning activities. [ 8–20 ] Biomimetic superhydrophobic surfaces can be prepared via different approaches, including reactive ion etching, [ 21 ] chemical/physical processing, [ 22–25 ] lithographing, [ 26,27 ] and coating. [ 28–33 ] Among these approaches, the coating approach has been widely applied, owing to its simple preparation process, low equipment requirement, and wide application range.…”

Robust platform for water harvesting and directional transport

“…Generally, there are two forms of water condensation of moisture from the air: filmwise condensation and dropwise condensation. [17][18][19] Filmwise condensation refers to the condensate liquid forming a continuous film, while dropwise condensation refers to the harvesting of condensate liquids in the form of droplets. In consideration of heat-transfer efficiency during phase-change, dropwise condensation is over ten times more than that of filmwise condensation, and the heat-transfer performance of dropwise condensation can be further improved by fabricating micro/nano-structures on the substrate.…”