The Dry‐Style Antifogging Properties of Mosquito Compound Eyes and Artificial Analogues Prepared by Soft Lithography

Abstract

Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material's surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis.[1] To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. [1][2][3][4][5][6][7] A well-known example is the use of photocatalytic TiO 2 nanoparticle coatings that become superhydrophilic under UV irradiation. [3,4] Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. [1,5,6] The key to these two "wet"-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, [7] including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently "wet" nature. Thus, a "dry"-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves [8][9][10] and the striking ability of a water-strider's legs to walk on water [11] can be attributed to the ideal superhydrophobicity of their surfaces, induced by special micro-and nanostructures. To date, the biomimetic fabrication of superhydrophobic micro-and/or nanostructures has attracted considerable interest, [12][13][14][15][16][17] and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, [1] there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale-so small that they can be easily trapped in the interspaces among mic...

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

“…[15][16][17][18][19][47][48][49] Herein, we show biological inspirations that guide the design and creation of CMDSP surfaces that own the remarkable self-removal ability of small-scale condensate microdrops. Gao et al [5] first reported that closely packed nanocones on the surface of mosquito eyes are fully nonsticky to condensed microdrops (Figure 1c-e), showing a dry-style antifogging function. Subsequently, Wisdom et al [6] reported that tiny condensate microdrops on the closely packed nanocone surface of cicada wings (Figure 1f) can selfremove by jumping via mutual coalescence, displaying a moisture self-cleaning function.…”

“…[31,50,51,[66][67][68][69] Third, the building blocks must have a certain height or depth to avoid the collapse of the suspended water bridges. [68] Following these design principles and inspired by nature, our group proposed and demonstrated that efficient self-propelling of small-scale condensed microdrops can be [5] Copyright 2007, Wiley-VCH. e) AFM image of closely packed conical nanonipples.…”

“…Inspired by nature, [1][2][3][4][5][6][7][8][9][10][11][12][13][14] the special wettability of material surfaces, which is engineered via synergistic utilization of microscale surface structures and surface chemistry has been one of the most active research fields, and it can play a key role in addressing problems related to energy, environment, resources, and health. Efforts in the past decades have explored controllable fabrication, functionality, and performance optimization of bionic superhydrophobic surfaces with a contact angle above 150°, and they have resulted in technological innovations such as self-cleaning, drag-reduction, anticorrosion, antifogging, antifreezing and oil-water separation.…”

Bio‐Inspired, Smart, Multiscale Interfacial Materials

“…However, recently some less complex, but nonetheless special features in biology received intense attention (Fig. 2), such as, the selfcleaning effect of lotus leaves and duck feathers, [34,35] the non-fogging, superhydrophobic compound eyes of mosquitoes, [36] the locomotion of geckos and octopuses via highly adhesive feet and suckers, [37,38] the non-wetting phenomenon of water striders walking on water, [39] the color of peacock feathers, butterfly wings, and beetle shells which is caused by a periodic microstructure, [40][41][42] the special nanostructures causing anti-reflectivity in cicada's wings and moth's compound eyes, [43,44] and lastly the special photonic reflectivity of sponge spurs due to their unique microstructure. [45] All these features are suitable for bio-inspiration.…”

Direct Imaging of Superwetting Behavior on Solid–Liquid–Vapor Triphase Interfaces

“…The design of optimal bioinspired materials commonly involves the special wettability of biological surfaces, such as rice leaves, [8a] fish scales, [53] and mosquito compound eyes. [54] Superhydrophobic phenomena of solid surfaces can be explained by the Cassie model theory. However, there is still a lack of sufficient visible evidence to prove that air is presented between the solid and the liquid.…”