Bionic Superhydrophobic Surface Research Articles

The Droplet Creeping-Sliding Dynamic Wetting Mechanism on Bionic Self-Cleaning Surfaces.

The dynamic wetting behavior of droplets has been of wide concern due to the hazards of accretion/icing of supercooled droplets on engineering components/systems served in low temperature freezing rain environment; thus, it is urgent to establish the relationship between droplet depinning/removing behaviors and surface characteristics. In this article, the actual rotation conditions of moving components such as wind turbine blades are simulated. The self-cleaning hydrophobic coating surface(S1) and bionic superhydrophobic coating surface(S2) show outstanding droplet removal performance compared to hydrophilic bare steel surface(S0), and the average speed of the droplet removal is increased by 400-500%. The "creeping-sliding" behavior of droplets on self-cleaning coatings is investigated by the change of droplet displacement(ΔD). The effect of the energy storage caused by the droplet creeping process provides initial kinetic energy for the droplet removal. Combined with the experimental data and theoretical model, the critical depinning resistance is calculated. The difference of the wetting interface free energy(ΔEx) during the dynamic wetting process of the droplets on the bionic superhydrophobic self-cleaning surface is researched. And the influence mechanism of the droplet embedded depth(x) on the creeping/sliding behavior in the nanotexture is clarified. Thus, the mechanical criterion of droplet depinning is proposed (the error is about 10%). The results can provide a theoretical basis for the design principle of antifreezing rain coatings on moving components.

Fabrication of bioinspired closed chute structure on TC4 surface by double laser beam ablation for enhanced dynamic anti-icing performance

The dynamic behavior of water droplets plays an important role in anti-icing performance, as when they impact on superhydrophobic surfaces, the rebound process effectively removes potential ice crystal nuclei on the surface, thereby reducing ice condensation and accumulation, ultimately preventing ice formation. In this study, inspired by the cuticle structure of springtails and the tilted arrangement of pigeon feathers, a bionic superhydrophobic surface with closed chute structure is proposed. The closed chute structure reduces the adhesion force between the surface and water droplets, enhancing directional rebounding ability and accelerating water droplets' separation from the surface for enhanced anti-icing performance. Considering the morphology of hierarchical closed structures is difficult to be regulated by single laser beam ablation, the superhydrophobic surface with closed chute structure is successfully fabricated by double laser beam ablation. This method optimizes the spatial distribution of the laser energy field by adjusting the rotation angle of the half-wave plate (HWP). By combining the analysis of micromorphology, elemental distribution, dynamic and static anti-icing tests etc., it is verified that the superhydrophobic surface with closed chute structure can improve the dynamic anti-icing performance, which provides a new method for anti-icing design in engineering field.

Blue-ringed Octopus inspired slippery coating with physico-chemical synergistic antifouling properties

Bionic superhydrophobic and slippery liquid-infused porous surfaces (SLIPS) have attracted great interest due to their antifouling properties, while the poor stability, complex preparation of porous structures and rapid loss of lubricants, as well as only possessing physical antifouling capability, have hindered their further application. Herein, inspired by the Blue-ringed Octopus’ defensive equipment of slippery skin and toxin secretion when faced with predators, an antifouling slippery coating containing repellent is easily prepared. The repellent capsaicin physically connected to the slippery networks can be activated to accelerate release in response to the changes in pH caused by bacterial secretions, and the adhesion resistance of the coating is improved by 99 % compared to aluminum plates, both conclusions confirmed by experimental and computational data. The anti-adhesive properties of the slippery surface, combined with the repellent properties of capsaicin provides the coating with excellent synergistic physico-chemical antifouling performance. This is demonstrated by the fact that the surface of the coating remains clear after contamination with proteins, bacteria and diatoms, as well as after 65 days of marine field testing. Additionally, the slippery surface has self-healing and outstanding anticorrosion ability. Therefore, the eco-friendly coating has promising application prospects in marine field for antifouling purposes.

Construction and parameter optimization of LPBF-NiTi alloy bionic superhydrophobic surface based on laser processing

Nickel-titanium (NiTi) is the most ordinarily used shape memory alloy (SMAs), which has important implications in aerospace, medical devices and so on. However, NiTi parts were limited in their application scope and ability due to the difficulty of processing. Until the appearance of laser powder bed fusion (LPBF) technology, it overcame NiTi alloy preparation's multiple challenges and became the preferred method to fabricate NiTi alloy. Nevertheless, the NiTi parts fabricated by LPBF that have a great shortage still exist in corrosion resistance. Therefore, in this paper, a series of micro-nano structures with different characteristics were constructed in LPBF-NiTi by orthogonal experiment for the first time, which wants to explore the degree of influence of various parameters on the wettability of samples. After variance analysis, the nanolaser processing parameters which are most suitable for constructing lotus leaf structures on NiTi alloy surfaces are obtained. The surface morphology and composition were studied by SEM, XRD, EDS, and XPS, respectively. Finally, the corrosion resistance of samples was tested by electrochemical analysis. The results show that the laser power during processing has the greatest influence on the surface morphology of LPBF-NiTi alloy. And the wettability is affected by surface morphology and –CF/-CF2 adsorption. Furthermore, we compared the corrosion resistance of the superhydrophobic samples which was obtained based on the variance analysis with that of the substrate in 3.5 wt% NaCl solution. The result shows that the corrosion resistance and corrosion stability of superhydrophobic samples are brilliantly increased compared with the substrate.

Superhydrophobic coating induced anti-icing and deicing characteristics of an airfoil

Aircraft icing seriously threatens flight safety. The widely used electrothermal anti/de-icing technology has high energy consumption and poor performance. The bionic superhydrophobic surface has anti-icing potential, which can be combined with electric heater technology to achieve energy savings and efficiency improvement. In the previous research, we developed a superhydrophobic coating with mechanochemical robustness for aircraft anti-icing and proved its excellent anti-icing performance. This research combines this coating with the graphene electric heater to obtain a coupling system and explores its anti-icing effect under aviation conditions through the ice wind tunnel test. The results showed that the coating significantly improves the anti-icing properties, delaying the icing process for 10 s, saving the anti-icing energy consumption by 21% compared with graphene heating alone, and increasing the deicing efficiency by 250%. When the coating protection area reaches 30% chord, it can achieve a 'dry' anti-icing state, and this coupling system saves energy by 60% compared with wire heating. Furthermore, The ‘honeycomb structure’ coating is better in anti-icing effect, and the ‘island structure’ coating has stronger anti-icing stability. The hydrophobicity of the coating is less affected by the high-speed droplet impact, so it has a long life expectancy in the active anti-icing mode. This study can provide new ideas for solving the problem of aircraft icing.

Biology and nature: Bionic superhydrophobic surface and principle.

Nature is the source of human design inspiration. In order to adapt to the environment better, creatures in nature have formed various morphological structures during billions of years of evolution, among which the superhydrophobic characteristics of some animal and plant surface structures have attracted wide attention. At present, the preparation methods of bionic superhydrophobic surface based on the microstructure of animal and plant body surface include vapor deposition, etching modification, sol-gel method, template method, electrostatic spinning method and electrostatic spraying method, etc., which have been used in medical care, military industry, shipping, textile and other fields. Based on nature, this paper expounds the development history of superhydrophobic principle, summarizes the structure and wettability of superhydrophobic surfaces in nature, and introduces the characteristics differences and applications of different superhydrophobic surfaces in detail. Finally, the challenge of bionic superhydrophobic surface is discussed, and the future development direction of this field is prospected.

A facile strategy to fabricate bionic superhydrophobic armor based on utilization of metallographic structure heredity and reconstruction of anodized oxide film on alloy

Focusing on alloy system, a facile strategy was proposed to fabricate a micro/nano-structured bionic superhydrophobic surface with enhanced anti-corrosion performance. It was implemented on iron carbon alloy substrate by combining one-step anodic oxidation with designed annealing to realize a protective armor. The study verified that the metallographic features in the alloy system and heredity during the anodic oxidation were crucial preconditions to construct bionic surface. The reconstruction of the anodized oxide films triggered by designed annealing changed the wetting mechanism as well as switching the hydrophilic/hydrophobic state by forming a smaller size point-to-point contact (Cassie-Baxter State) with the droplets. The synergistic effect of this unique bionic structures and low surface energy coating made the sample surface exhibit superhydrophobic state and excellent corrosion resistance. Such combination strategy lays the foundation for constructing functional surfaces of alloy systems. More importantly, it can be extended to multicomponent alloy systems, by selecting structure features even modulating feature components to simply realize a devisable protective armor, which provides more in-depth thinking for solving the longstanding corrosion problems of engineering materials.

Bionic superhydrophobic surfaces based on topography of copper oxides

AbstractSuperhydrophobic surfaces (SHSs) exist in many biological organisms endowed by spectacular surface topographies, which provide important insights to drive a paradigm shift in design of engineering surfaces. Based on this, extensive progresses have been developed on bionic superhydrophobic strategies. Among them, SHSs based on topography of copper oxides exhibit considerable application prospects because of the steerability and diversity of topography, as well as additional performances, such as antibiosis, anticorrosion and catalysis. We first present a brief overview of the discovery of natural SHSs as well as fundamental understanding of surface wetting performance. Then, the structural effects in superhydrophobic systems based on the topographies of biological organisms and copper oxides are described. Finally, we highlight the perspectives on the novel design strategies of copper oxide‐based SHSs that adapt to various practical applications.

Biomimetic superhydrophobic metal/nonmetal surface manufactured by etching methods: A mini review.

As an emerging fringe science, bionics integrates the understanding of nature, imitation of nature, and surpassing nature in one aspect, and it organically combines the synergistic complementarity of function and structure–function integrated materials which is of great scientific interest. By imitating the microstructure of a natural biological surface, the bionic superhydrophobic surface prepared by human beings has the properties of self-cleaning, anti-icing, water collection, anti-corrosion and oil–water separation, and the preparation research methods are increasing. The preparation methods of superhydrophobic surface include vapor deposition, etching modification, sol–gel, template, electrostatic spinning, and electrostatic spraying, which can be applied to fields such as medical care, military industry, ship industry, and textile. The etching modification method can directly modify the substrate, so there is no need to worry about the adhesion between the coating and the substrate. The most obvious advantage of this method is that the obtained superhydrophobic surface is integrated with the substrate and has good stability and corrosion resistance. In this article, the different preparation methods of bionic superhydrophobic materials were summarized, especially the etching modification methods, we discussed the detailed classification, advantages, and disadvantages of these methods, and the future development direction of the field was prospected.

Coalescence-Induced Droplet Jumping on Honeycomb Bionic Superhydrophobic Surfaces.

Condensation-induced jumping of droplets on superhydrophobic surfaces has received extensive attention because of its great potential for applications in areas such as condensation enhancement and self-cleaning. However, the jumping efficiency of droplets on flat superhydrophobic surfaces is very low, and there is no reliable means of achieving efficient droplet jumping on large scales, which greatly limits its application. To this end, we developed a class of honeycomb bionic superhydrophobic surfaces (HBSS) that enable reliable and efficient droplet jumping on a large scale for the first time and performed experimental and simulation studies on droplet condensation and jumping on this kind of surface. Condensation experiments show that condensate droplets on HBSS can be effectively positioned under the influence of gravity and the uniformity of the droplet diameter is ensured, laying the foundation for achieving efficient jumping. The shape and geometric parameters of HBSS have a significant impact on the droplet jumping efficiency, and the maximum dimensionless jumping velocity of droplet jumping was experimentally measured to be 0.747, corresponding to an efficiency of about 45.25%. Combining with the results of simulation calculations, we found that the surface structure of HBSS can promote more of the excess surface energy to net upward kinetic energy along an extremely efficient and simple pathway (direct conversion), thus achieving an energy conversion efficiency of over 45%.

3D-printed bionic superhydrophobic surface with petal-like microstructures for droplet manipulation, oil-water separation, and drag reduction

Recently, bioinspired mushroom or reentrant mushroom microstructures have attracted intersts of researchers for their amazing water superrepellence property. However, basic principles of exquisite microstructures design for improving water repellence are still lacking. This paper reports a novel 3D-printed biomimetic superhydrophobic surface with petal-like microstructures inspired by the droplet pinning effect of nepenthes peristome. Then, parameters such as petal number, petal proportion and spacing distance are studied and optimized to improve water repellence, which is evaluated according to droplet bearing capacity. The results show that when the petal number is 4, the spacing distance is 100 μm, and the petal proportion is 50%, the petal-like structured surface achieves its maximum droplet bearing capacity. Comparing with the common mushroom microstructures, the maximum increase rate in bearing capacity is 58.3% for the optimized petal-like microstructures. Corresponding mechanism analysis attributes such superrepellence property to the sharp edge effect and the arch curve effect. Furthermore, the excellent water repellence enables the petal-like microstructured surface to be used for water droplets manipulation, oil-water separation, and captured-air drag reduction.

Improved Stable Drag Reduction of Controllable Laser-Patterned Superwetting Surfaces Containing Bioinspired Micro/Nanostructured Arrays.

Superwetting surfaces are widely used in many engineering fields for reducing energy and resistance loss. A facile and efficient method using laser etching has been used to fabricate and control superwettable drag reduction surfaces. Inspired by the self-cleaning theory of lotus leaves, we propose controllable patterned bionic superhydrophobic surfaces (BSSs) simulating the uneven micro/nanostructures of lotus leaves. The superhydrophobicity and drag reduction ratios at low velocities are highly improved using a laser ablation method on metal substrates. However, unstable air layers trapped on superhydrophobic surfaces are usually cut away by a high-velocity flow, which greatly reduces the drag reduction performance. The fabricated bionic superhydrophobic/hydrophilic surfaces (BSHSs) with alternated hydrophilic strips can build a large surface energy barrier to bind the three-phase contact line. It maintains the stable drag reduction by capturing the air bubbles attached to the hydrophilic strips at a high velocity. Three-dimensional simulation analysis and equipment to measure the weak friction of a self-assembled solid–liquid interface are used to explain the drag reduction mechanism and measure the drag reduction ratios at different flow speeds. BSSs achieve an improved drag reduction effect (maximum 52.76%) at a low velocity (maximum 1.5568 m/s). BSHSs maintain an improved and steady drag reduction effect at high speed. The drag reduction ratios can be maintained at about 30% at high speed, with a maximum value of 4.448 m/s. This research has broad application prospects in energy saving, liquid directional transportation, and shipping due to their robust superhydrophobic properties and stable drag reduction effect.

Recent advances in bioinspired superhydrophobic ice-proof surfaces: challenges and prospects.

Bionic superhydrophobic ice-proof surfaces inspired by natural biology show great potential in daily life. They have attracted wide research interest due to their promising and wide applications in offshore equipment, transportation, power transmission, communication, energy, etc. The flourishing development of superhydrophobic ice-proof surfaces has been witnessed due to the availability of various fabrication methods. These surfaces can effectively inhibit the accumulation of ice, thereby ensuring the safety of human life and property. This review highlights the latest advances in bio-inspired superhydrophobic ice-proof materials. Firstly, several familiar cold-resistant creatures with well-organized texture structures are listed briefly, which provide an excellent template for the design of bioinspired ice-proof surfaces. Next, the advantages and disadvantages of the current techniques for the preparation of superhydrophobic ice-proof surfaces are also analyzed in depth. Subsequently, the theoretical knowledge on icing formation and three passive ice-proof strategies are introduced in detail. Afterward, the recent progress in improving the durability of ice-proof surfaces is emphasized. Finally, the remaining challenges and promising breakthroughs in this field are briefly discussed.

Application of Bionic Superhydrophobic Surface in Jaw End Face of Microgripper

Application of Bionic Superhydrophobic Surface in Jaw End Face of Microgripper

Progress in fabrication and applications of micro/nanostructured superhydrophobic surfaces

Natural biological surfaces such as lotus leaves and water striders have micro- and nanostructures and low-surface-energy materials, possessing excellent superhydrophobicity. It has become an important research topic to construct bionic superhydrophobic surfaces and explore their functional applications. This paper reviews the research progress on the fabrication and applications of superhydrophobic surfaces with micro/nanostructures. The techniques used for fabricating superhydrophobic surfaces, including the template method, nano-imprinting technique, laser-treatment, plasma treatment, electrospinning technique, solution-chemical etching method, electrochemical technique, phase separation method and sol–gel process, were introduced. Also, the diverse functional applications of superhydrophobic surfaces such as self-cleaning, anti-icing, oil–water separation, anti-corrosion and drag reduction were summarised. It is believed that green fabrication will become the future development direction of superhydrophobic surfaces. Further exploration for the superhydrophobic surfaces with mechanical stability and durability will be expected to expand the application prospect and commercial value of superhydrophobic surfaces.

One-step Condensation/copolymerization of VTES and DVB for Self-assembly Bionic Superhydrophobic Surface Coating and Study on Oil-water Separation

One-step Condensation/copolymerization of VTES and DVB for Self-assembly Bionic Superhydrophobic Surface Coating and Study on Oil-water Separation

One-step method using laser for large-scale preparation of bionic superhydrophobic & drag-reducing fish-scale surface

In this study, four bionic fish-scale models were extracted and produced based on the microscopic morphology and the arrangement of scales on the body of Sciaenops ocellatus. A simple, quick and low-cost method using laser was introduced for fabricating the bionic fish-scale surface on aluminum (Al) alloy. Under the action of laser beams, the fish-scale morphology with inclined surface was obtained by controlling the density of laser path and processing times. Biomimetic fish-scale surfaces with different sizes were produced through adjusting the four ratios of fish scale graph. Then wettability test was performed on different samples. Our results showed that all the samples were hydrophobic and the sample with 100% zoom ratio demonstrated excellent superhydrophobicity and low adhesion. Furthermore, we tested the drag reduction performance of the sample with zoom ratio of 100%. The experimental results indicated that under different flow conditions, the sample exhibited different performance values in drag reduction, and the drag reduction rate could reach 4.814% under laminar conditions. This study provided a simple method from the perspective of bionics to fabricate a bionic superhydrophobic surface with drag reduction performance, providing positive guidance for the fabrication of underwater drag-reducing surface.

A Myristic Acid/n-Dodecyltrimethoxysilane Bilayer Coating on Magnesium Alloy with Corrosion-Inhibition Bionic Superhydrophobic Surface

Abstract A superhydrophobic bilayer surface was created with a contact angle (CA) of 157.3 ± 1° and sliding angle (SA) of 2° ± 0.5° using a simple one-step solvothermal process. The bionic micro/nano structures are similar to the flower of a carnation and common sowthistle, which plays an important role in resisting corrosion. In addition, potentiodynamic polarization shows that the superhydrophobic bilayer surface has excellent corrosion resistance. This preparation is beneficial as it is simple to fabricate, low cost, is easily prepared across large areas, and has excellent corrosion resistance, amongst other benefits. It can effectively broaden the application of magnesium alloys and extend to other conductive metal materials.

Numerical investigation on aerodynamic performance improvement of vertical-axis tidal turbine with super-hydrophobic surface

Inspired by nature, more and more domestic and foreign scholars began to pay attention to the application of hydrophobic materials in various fields for military and civil applications. The suitable bionic super-hydrophobic surface (SHS) has high drag reduction effect because of the slip effect on the solid surface. This paper conducted numerical simulation to study the aerodynamic performance improvement of vertical-axis tidal turbine (VATT) with SHS on the airfoils. The influence of different inflow velocities, blade number and solidities of VATT with SHS are studied. The results show that the maximum energy efficiency can be increased by 16.5% at the inflow velocity U = 3 m/s. The improvement of power coefficient is found greatly influenced by the inflow velocity, blade number and solidity at small tip-speed ratios, while the increment of the energy efficiency is almost independent to these aerodynamic parameters at high tip-speed ratios.

Adsorption and superficial transport of oil on biological and bionic superhydrophobic surfaces: a novel technique foroil-water separation.

Superhydrophobicity is a physical feature of surfaces occurring in many organisms and has been applied (e.g. lotus effect) in bionic technical applications. Some aquatic species are able to maintain persistent air layers under water (Salvinia effect) and thus become increasingly interesting for drag reduction and other 'bioinspired' applications. However, another feature of superhydrophobic surfaces, i.e. the adsorption (not absorption) and subsequent superficial transportation and desorption capability for oil, has been neglected. Intense research is currently being carried out on oil-absorbing bulk materials like sponges, focusing on oleophilic surfaces and meshes to build membranes for oil-water separation. This requires an active pumping of oil-water mixtures onto or through the surface. Here, we present a novel passive, self-driven technology to remove oil from water surfaces. The oil is adsorbed onto a superhydrophobic material (e.g. textiles) and transported on its surface. Vertical and horizontal transportation is possible above or below the oil-contaminated water surface. The transfer in a bioinspired novel bionic oil adsorber is described. The oil is transported into a container and thus removed from the surface. Prototypes have proven to be an efficient and environmentally friendly technology to clean oil spills from water without chemicals or external energy supply. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 3)'.