Shichao Niu

Excellent Structure-Based Multifunction of Morpho Butterfly Wings: A Review

Morpho butterfly, famous for its iridescence wing scales, has gradually evolved a diversity of functions and has attracted much attention recently. On the other hand, it is known that the wing surface of Morpho butterfly has some complex and sophisticated structures. In fact, they are composed of an alternating multilayer film system of chitin and air layers, which have different refractive indexes. More importantly, these structures can interact strongly with visible light because the feature size of the structures is in the same order of magnitude with light wavelength. It is noteworthy that it is these optical architectures that cause the excellent multifunction including structural color, antireflection, thermal response, selective vapour response, directional adhesion, superhydrophobicity and so on. This review mainly covers the excellent multifunctional features of Morpho butterfly wings with representative functional structures of multilayer film system, photonic crystal and ridges. Then, the mechanism of the structure-based optical multifunction of Morpho butterfly is analyzed. In order to facilitate mechanism analysis, the models of bionic functional structures are reported, as well as the interaction process between the multiscale structures and the external media It is concluded that these functions of Morpho butterfly wings have inevitable and corresponding regularity connection with the structural parameters and the dielectric coefficient of the filled medium. At last, the future direction and prospects of this field are briefly addressed. It is hoped that this review could be beneficial to provide some innovative inspirations and new ideas to the researchers in the fields of engineering, biomedicine, and materials science.

A High-Transmission, Multiple Antireflective Surface Inspired from Bilayer 3D Ultrafine Hierarchical Structures in Butterfly Wing Scales

A high-transmission, multiple antireflective surface inspired by bilayer 3D ultrafine hierarchical structures in butterfly wing scales is fabricated on a glass substrate using wet chemical biomimetic fabrication. Interestingly, the biomimetic antireflective surface exhibits excellent antireflective properties and high transmission, which provides better characteristics than the butterfly wings and can significantly reduce reflection without losing transparency. These findings offer a new path for generating nanostructured antireflectors with high transmission properties.

Erosion-Resistant Surfaces Inspired by Tamarisk

Tamarisk, a plant that thrives in arid and semi-arid regions, has adapted to blustery conditions by evolving extremely effective and robust anti-erosion surface patterns. However, the details of these unique properties and their structural basis are still unexplored. In this paper, we demonstrate that the tamarisk surface only suffers minor scratches under wind-sand mixture erosion. The results show that the anti-erosion property of bionic sample, inspired by tamarisk surface with different surface morphologies, can be attributed to the flow rotating in the grooves that reduces the particle impact speed. Furthermore, the simulation and experiment on the erosion wear behavior of the bionic samples and bionic centrifugal fan blades show that the bionic surface with V-type groove exhibits the best erosion resistance. The bionic surface on centrifugal fan blades with optimum parameters can effectively improve anti-erosion property by 28.97%. This paper show more opportunities for bionic application in improving the anti-erosion performance of moving parts that work under dirt and sand particle environment, such as helicopter rotor blades, airplane propellers, rocket motor nozzles, and pipes that regularly wear out from erosion.

Characterization of Multi-scale Morphology and Superhydrophobicity of Water Bamboo Leaves and Biomimetic Polydimethylsiloxane (PDMS) Replicas

The morphology and wettability of Water Bamboo Leaves (WBL) and their biomimetic replicas were investigated. The particular morphology structures of samples were characterized by Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). The static wettability of samples was assessed by contact angle measurements, while the dynamic wettability was analyzed by high speed camera system. The wettability mechanism of WBL was also explained by Cassie model. Artificial surfaces were fabricated by duplicating WBL surface microstructures using PDMS in large area (5 cm × 3 cm). The results show the main structure characteristics of this leaf surface are sub-millimeter groove arrays, micron-scale papillae and a superimposed layer with 3D epicuticular wax sculptures hierarchical structure, and the static Water Contact Angle (WCA) of 151°±2° and Water Sliding Angle (WSA) of 4°–6° indicate that WBL surface is superhydrophobic. The combination of wax film and microstructure of WBL surface gives its surface excellent superhydrophobic property. Complex hierarchical patterns with features from sub-millimeter to micron-scale range are well reproduced. The reason for the absence of nanostructures is melting of plant epidermal wax during the curing process. The WCA values on artificial WBL and negative PDMS replica are 146° ± 3° and 137° ± 2°, respectively, demonstrating preferable hydrophobicity. Differences in wetting behavior between natural leaves and artificial leaves originate from an inaccurate replication of the chemistry and structures of the three-dimensional wax projections on the leaf surface. Nevertheless, the morphological features of the leaf transferred to the replica improve significantly the hydrophobic properties of the replica when compared with the smooth PDMS reference. This study may provide an inspiration for the biomimetic design and construction of large area roughness-induced hydrophobic and anti-sticking material surface.

Energy-Efficient Oil–Water Separation of Biomimetic Copper Membrane with Multiscale Hierarchical Dendritic Structures

Membrane-based materials with special surface wettability have been applied widely for the treatment of increasing industrial oily waste water, as well as frequent oil spill accidents. However, traditional technologies are energy-intensive and limited, either by fouling or by the inability of a single membrane to separate all types of oil-water mixtures. Herein, a biomimetic monolayer copper membrane (BMCM), composed of multiscale hierarchical dendritic structures, is cleverly designed and successfully fabricated on steel mesh substrate. It not only possesses the ability of energy-efficient oil-water separation but also excellent self-recovery anti-oil-fouling properties (<150 s). The BMCM even keeps high separation efficiency (>93%) after ten-time cycling tests. More importantly, it retains efficient oil-water separation capacity for five different oils. In fact, these advanced features are benefited by the synergistic effect of chemical compositions and physical structures, which is inspired by the typical nonwetting strategy of butterfly wing scales. The findings in this work may inspire a facile but effective strategy for repeatable and antipollution oil-water separation, which is more suitable for various applications under practical conditions, such as wastewater treatment, fuel purification, separation of commercially relevant oily water, and so forth.

Flourishing Bioinspired Antifogging Materials with Superwettability: Progresses and Challenges

Antifogging (AF) structure materials found in nature have great potential for enabling novel and emerging products and technologies to facilitate the daily life of human societies, attracting enormous research interests owing to their potential applications in display devices, traffics, agricultural greenhouse, food packaging, solar products, and other fields. The outstanding performance of biological AF surfaces encourages the rapid development and wide application of new AF materials. In fact, AF properties are inextricably associated with their surface superwettability. Generally, the superwettability of AF materials depends on a combination of their surface geometrical structures and surface chemical compositions. To explore their general design principles, recent progresses in the investigation of bioinspired AF materials are summarized herein. Recent developments of the mechanism, fabrication, and applications of bioinspired AF materials with superwettability are also a focus. This includes information on constructing superwetting AF materials based on designing the topographical structure and regulating the surface chemical composition. Finally, the remaining challenges and promising breakthroughs in this field are also briefly discussed.

Integrated super-hydrophobic and antireflective PDMS bio-templated from nano-conical structures of cicada wings

Inspired by cicada wings that can greatly minimize the reflectivity on their surfaces over broad angles or frequency ranges due to the presence of tapered pillar arrays, we fabricated a polydimethylsiloxane (PDMS) positive replica of cicada wings, which demonstrated antireflective and super-hydrophobic characters. Firstly, the cicada wings were selected as a template to duplicate a SiO2 negative replica. Then, the SiO2 negative replica was used as a secondary template to prepare a PDMS positive replica. The resultant PDMS replica inherited the nano-conical structures and thus exhibited outstanding antireflective effect. A suppression of reflectance to a minimum of 0.7% that benefits from nano-cones has been achieved, since the path length and quantity of the incident light irradiated onto PDMS could be increased by incorporating anti-reflective and light scattering patterns. In the meantime, the PDMS replica demonstrates super-hydrophobicity due to the presence of nano-cone structures. The PDMS replica of cicada wings that possesses both anti-reflective and superhydrophobic properties may hold great promise for applications in anti-reflection and self-cleaning windows, in photovoltaic cells, telescopes, camera lenses, glass windows and beyond.

An Efficient Bionic Anti-Erosion Functional Surface Inspired by Desert Scorpion Carapace

To improve the particle erosion resistance of mechanical surfaces, a bionic coupling method inspired by the morphology and flexibility of desert scorpion (Androctonus australis) carapace was proposed in this study. The finite element method based on ANSYS/FLUENT was applied to examine the erosion resistance of a bionic V-shaped model. Subsequently, an experimental research was carried out to compare the particle erosion resistance performance of three types of specimens, namely, smooth, bionic V-shaped, and bionic V-shaped and flexibility coupling. Surface erosion microstructure was also examined under a stereoscopic microscope and a scanning electron microscope to characterize erosive damage. The anti-erosion property of the coupling and V-shaped specimens increased by approximately 74.7 and 57.4% compared to that of the smooth specimen in a 10-min test. The mechanism of particle erosion resistance is also discussed in detail. The particle impact marks that were distributed on the surfaces of both of the V-shaped and coupling specimens were regular.

Numerical Analysis of Erosion Caused by Biomimetic Axial Fan Blade

Damage caused by erosion has been reported in several industries for a wide range of situations. In the present work, a new method is presented to improve the erosion resistance of machine components by biomimetic method. A numerical investigation of solid particle erosion in the standard and biomimetic configuration blade of axial fan is presented. The analysis consists in the application of the discrete phase model, for modeling the solid particles flow, and the Eulerian conservation equations to the continuous phase. The numerical study employs computational fluid dynamics (CFD) software, based on a finite volume method. User-defined function was used to define wear equation. Gas/solid flow axial fan was simulated to calculate the erosion rate of the particles on the fan blades and comparatively analyzed the erosive wear of the smooth surface, the groove-shaped, and convex hull-shaped biomimetic surface axial flow fan blade. The results show that the groove-shaped biomimetic blade antierosion ability is better than that of the other two fan blades. Thoroughly analyze of antierosion mechanism of the biomimetic blade from many factors including the flow velocity contours and flow path lines, impact velocity, impact angle, particle trajectories, and the number of collisions.

Anti-adhesive Property of Maize Leaf Surface Related with Temperature and Humidity

The anti-adhesive surfaces have always aroused great interest of worldwide scientists and engineers. But in practical applications, it often faces the threat and impact of temperature and humidity. In this work, the excellent anti-adhesive performance of maize leaf under high temperature and humidity were investigated in detail. Firstly, the adhesion forces of the maize leaf surface under different temperature and humidity were measured by using Atomic Force Microscopy (AFM). The temperature of the substrate was varied between 23 °C to 100 °C, and the ambient relative humidity is from 18% to 100%. It was found that the adhesion force of maize leaf decreased with the increase of temperature and humidity. The mechanism of its excellent anti-adhesive performance of maize leaf under high temperature and relative humidity was revealed. The transverse and longitudinal ridges on maize leaf surface interlace with each other, forming small air pockets, which reduces the actual contact area between the object and the maize leaf. With the increase of humidity, the liquid film will be formed in the air pockets gradually and so much water vapor is produced with increase of temperature. Then the air flow rate increases though the wavy top of transverse ridges, inducing the dramatic decrease of adhesion force. Inspired by this mechanism, four samples with this bionic structure were made. This functional “biomimetic structure” would have potential value in the wide medical equipments such as high frequency electric knife with anti-adhesion surface under high temperature and high humidity.