Condensation Behavior of Hierarchical Nano/Microstructured Surfaces Inspired by Euphorbia myrsinites

Abstract

In nature, many extant species exhibit functionalized surface structures during evolution. In particular, wettability affects the functionalization of the surface, and nano/microstructures have been found to enable functions, such as droplet jumping, thereby making self-cleaning, antifog, antibacterial, and antireflection surfaces. Important efforts are underway to understand the surface structure of plant leaves and establish rational design tools for the development of new engineering materials. In this study, we focused on the hierarchical nano/microstructure of the leaves of Euphorbia myrsinites (hereinafter, E. myrsinites), which has a hierarchical shape with microsized papillae, covered with nanosized protruding wax, and observed the condensation behavior on the leaf surface. Si is vertically etched via reactive ion etching (RIE) to artificially mimic the hierarchical nano/microstructures on the leaves of E. myrsinites. We made four types of artificial hierarchical structures, with micropillars having pillar diameters of 5.6 and 16 μm (pillar spacing of 20 and 40 μm, respectively) and heights of 6.5 and 19.5 μm, and nanopillars formed on the surface. The optical observation with a microscope revealed a very high density of condensed droplets on the artificial surface and a stable jumping behavior of droplets of 10 μm or more. Furthermore, in the samples with a micropillar diameter of 5.6 μm and a micropillar height of 19.5 μm, the droplets that had jumped and fallen thereupon bounced off, thereby preventing reattachment. As a result, no droplets of 35 μm or more could exist even after 10 min. In addition, it was clear that a small underlying droplet of less than 10 μm was generated at the bottom of the relatively large secondary droplet existing on the large micropillar of 16 μm, and a frequent coalescence of the droplets occurred. This study revealed the phenomenon of condensation on the surface of plants as well as made it possible to improve the heat exchange process by significantly promoting the heat transfer of condensation using artificial surfaces.

Recent advances in prevailing antifogging surfaces: structures, materials, durability, and beyond

“…2A). Inspired by E. myrsinites , Baba et al 27 fabricated biomimetic microcolumn arrays with superhydrophobicity and low adhesion on silicon wafers. Optical observation by microscope revealed that when the height of the microcolumn reached 6.5 μm, the mass transfer coefficient increased rapidly with the steam diffusion rate, and the greater disturbance of the local mass transfer boundary layer provided the corresponding abundant steam for the formation and growth of the bottom droplets; thus tiny droplets are formed at the bottom of the coalesced droplets, which grow and merge with the secondary droplets to motivate the continuous jump of surface droplets (Fig.…”

Robust and durable liquid-repellent surfaces

“…Meanwhile, condensate micro droplets on liquid-repellent surfaces with nanostructures could be selfpropelled since the coalescence-released excess surface energy was much larger than the interface adhesion-induced energy dissipation. 51,183,[443][444][445][446][447][448] For example, as shown in Fig. 33, Wang et al demonstrated that condensate micro droplets on a superhydrophobic surface with closely packed aligned ZnO nanoneedles could be self-removed by mutual coalescence-induced jumping, and the surface thereby maintained long-term water repellence in extreme vapor conditions.…”

“…74a, also see Section 4.2.2) are desired for heat transfer enhancement. [33][34][35]51,443,444,446,448,687 For example, Miljkovic et al prepared nanostructured CuO films on Cu tube surface by chemical oxidation in a hot alkaline solution composed of NaClO 2 , NaOH, Na 3 PO 4 Á12H 2 O, and deionized water (3.75 : 5 : 10 : 100 wt%), which were then functionalized by using CVD of a fluorinated silane (trichloro(1H,1H,2H,2Hperfluorooctyl)silane). 687 As shown in Fig.…”

Phyllostachys Viridis-Leaf-like MLMN Surfaces Constructed by Nanosecond Laser Hybridization for Superhydrophobic Antifogging and Anti-Icing

“…Steam condensation/droplet freezing on solid surfaces can cause serious economic and safety problems. − Thus, highly efficient antifogging/anti-icing approaches are vital in many engineering applications, involving aerospace, wind/photovoltaic power generation, refrigeration, transportation, and power communication. − Typical solutions to these problems are achieved by using active deicing systems such as electrothermal heating devices. However, the abovementioned methods have their limitations, such as high energy consumption, low efficiency, and nonenvironmental protection.…”