Multiple Superwettable Nanofiber Arrays Prepared by a Facile Dewetting Strategy via Controllably Localizing a Low‐Energy Compound

Superwettable solid surfaces have attracted substantial research interest due to their outstanding performance. Various approaches have been developed for preparing superwettable surfaces via constructing a highly textured surface roughness and/or altering the surface free energy. Here, a facile dewetting strategy is proposed to produce multiple superwettabilities on copper hydroxide nanofiber arrays (Cu(OH)₂‐NFAs) by controlling the localized state of low‐energy silicone oil. It is proposed that both the capillary forces along each nanofiber and the evaporation of the octane solvent contribute to the localization of the silicone oil in the NFAs. By varying the concentration of the silicone oil, its localized state changes from a scattered discontinuous distribution to a continuous thin/thick film, which leads to variations in the surface energy and surface roughness. Consequently, Cu(OH)₂‐NFAs with superhydrophilicity, superhydrophobicity with both high and low adhesion, and super slippery properties are prepared. Notably, a very small amount of silicone oil can alter the surface wettability of the Cu(OH)₂‐NFAs from superhydrophilic to superhydrophobic, which is attributable to the migration of silicone oil to the top of the nanofibers during the dewetting process. These results will provide new insights on the facile fabrication of functional surfaces with multiple superwettabilities.     

Fabrication and Characterization of Superhydrophobic Surfaces with Dynamic Stability

Superhydrophobic surfaces of dynamic stability are crucial for applications in water‐repellent materials. In this work, a hierarchical structure composed of a dendritic microporous surface with nanostructured porosity is demonstrated that shows robust superhydrophobicity with dynamic stability. The hierarchical structures are obtained on both copper foils and wires by a dynamic gas‐bubble template‐assisted electrochemical deposition method. The substrates can then be modified with alkyl thiols to obtain the surface superhydrophobicity. A new kind of testing, mechanical monitor‐assisted continuous water surface strokes, is developed to reveal the dynamic stability of the as‐prepared superhydrophobic copper wires. The as‐prepared superhydrophobic copper wires can exert a high propulsive force, and particularly, show little adhesive force in the process of continuous strokes on the water surface, exhibiting robust superhydrophobicity with dynamic stability. The approach allows a strategy for the fabrication of superhydrophobic surfaces with dynamic stability, and suggests a new method to evaluate the dynamic stability of superhydrophobic surfaces.     

Fabric-Based TENG Woven with Bio-Fabricated Superhydrophobic Bacterial Cellulose Fiber for Energy Harvesting and Motion Detection

Fabric-based triboelectric nanogenerators (TENGs) exhibit superior output performance, flexibility, and wearability. However, the fabric structure often creates gaps that accumulate contaminants, which weaken the performance and durability of the TENGs. To address this challenge, a novel eco-friendly superhydrophobic fabric-based TENG (SF-TENG) woven with superhydrophobic electroconductive bacterial cellulose fiber (SEBC fiber) is presented. To construct durable superhydrophobicity, an ingenious bio-fabricated method is employed for the shell–core structure. SEBC fibers with bio-fabricated shell–core structure exhibit excellent electroconductibility, mechanical property, biodegradability, and durable superhydrophobicity. SF-TENG displays a maximum open-circuit voltage of 266.0 V, a short-circuit current of 5.9 µA, and an output power of 489.7 µW, and successfully powers devices such as stopwatch and calculator. Abilities of self-cleaning and anti-fouling guarantee the stable output performance of SF-TENG under harsh environmental conditions such as liquids pouring. Furthermore, the intelligent clothing is designed based on SF-TENG to detect motion signals, and it is further utilized to construct a Sports and Health Monitoring System as a deep application. In summary, this study provides a novel strategy of bio-fabrication for the design and preparation of superhydrophobic electroconductive fiber with shell–core structure. The SF-TENG demonstrates practicability, stability and is promising for wearable devices in harsh environmental conditions.     

Improved Interfacial Floatability of Superhydrophobic/Superhydrophilic Janus Sheet Inspired by Lotus Leaf

Interfacial materials exhibiting superwettability have emerged as important tools for solving the real‐world issues, such as oil‐spill cleanup, fog harvesting, etc. The Janus superwettability of lotus leaf inspires the design of asymmetric interface materials using the superhydrophobic/superhydrophilic binary cooperative strategy. Here, the presented Janus copper sheet, composed of a superhydrophobic upper surface and a superhydrophilic lower surface, is able to be steadily fixed at the air/water interfaces, showing improved interfacial floatability. Compared with the floatable superhydrophobic substrate, the Janus sheet not only floats on but also attaches to the air–water interface. Similar results on Janus sheet are discovered at other multiphase interfaces such as hexane/water and water/CCl₄ interfaces. In accordance with the improved stability and antirotation property, the microboat constructed by a Janus sheet shows the reliable navigating ability even under turbulent water flow. This contribution should unlock more functions of Janus interface materials, and extend the application scope of the binary cooperative materials system with superwettability.     

Corrosion‐Resistant Superhydrophobic Coatings on Mg Alloy Surfaces Inspired by Lotus Seedpod

Superhydrophobic surfaces are widely found in nature, inspiring the development of excellent antiwater surfaces with barrier coatings isolating the underlying materials from the external environment. Here, the naturally occurring superhydrophobicity of lotus seedpod surfaces is reported. Protective coatings that mimic the lotus seedpod are fabricated on AZ91D Mg alloy surfaces with the synergistic effect of robust superhydrophobicity and durable corrosion resistance. The predesigned titanium dioxide films are coated on AZ91D by an in situ hydrothermal synthesis technique. Through sonication assisted electroless plating combined with a self‐assembling method, the densely packed Cu‐thiolate layers are uniformly plated with robust adhesion on the Mg alloy substrate, which function as a superhydrophobic barrier that can hold back the transport of water and corrosive ions contained such as Cl^?. Notably, the two extreme wetting behaviors (superhydrophilicity and superhydrophobicity) as well as corrosion resistance and improved corrosion resistance can be easily controlled by removal of the hydrophobic materials (n ‐dodecanethiol) at elevated temperature (350 °C) and modifying them at room temperature for 18 cycles, indicative of exceptional adhesion between the superhydrophobic coating and the underlying AZ91D Mg alloy.     

三级微纳超疏水表面的超快激光复合制备及防除冰性能研究

本文针对超疏水表面的防除冰性能,采用超快激光结合化学氧化的复合制备方法,开发了一类新的三级微纳超疏水表面结构,这类结构由微米锥阵列支撑结构以及在其上密集生长的金属氧化物纳米草结构和弥散分布的微米或亚微米花结构组合而成。经过表面改性后,这类三级微纳结构具有优异的超疏水性,其接触角可超过160°,滚动角在1°以内。对这类三级微纳超疏水表面的防结冰性能进行研究后发现,在冷凝和低温环境下,该类超疏水表面存在合并诱导自跳跃以及分级冷凝的现象,分级冷凝不仅可使表面上的一级冷凝液滴在高湿度环境下依然保持Cassie状态,还能使液滴在结冰前脱离表面,因此具有较好的防结冰性能;此外,由于表面三级微纳粗糙结构中捕获的空气囊具有较好的隔热作用,因此该超疏水表面具有良好的延迟结冰性能,其延迟异质形核的时间达到了52 min 39 s。最后,本文对三级微纳超疏水表面的疏冰性能进行了研究,结果表明:三级微纳超疏水表面的冰粘附强度仅为6 kPa,约为未经处理的铝合金表面的1/40;经过10次推冰测试后,该超疏水表面的冰粘附强度依然不超过20 kPa,说明该表面具有良好的机械耐久性,应用潜力巨大。     

Bio‐Inspired Multifunctional Metallic Foams Through the Fusion of Different Biological Solutions

Nature is a school for scientists and engineers. Inherent multiscale structures of biological materials exhibit multifunctional integration. In nature, the lotus, the water strider, and the flying bird evolved different and optimized biological solutions to survive. In this contribution, inspired by the optimized solutions from the lotus leaf with superhydrophobic self‐cleaning, the water strider leg with durable and robust superhydrophobicity, and the lightweight bird bone with hollow structures, multifunctional metallic foams with multiscale structures are fabricated, demonstrating low adhesive superhydrophobic ­self‐cleaning, striking loading capacity, and superior repellency towards different corrosive solutions. This approach provides an effective avenue to the development of water strider robots and other aquatic smart devices floating on water. Furthermore, the resultant multifunctional metallic foam can be used to construct an oil/water separation apparatus, exhibiting a high separation efficiency and long‐term repeatability. The presented approach should provide a promising solution for the design and construction of other multifunctional metallic foams in a large scale for practical applications in the petro‐chemical field. Optimized biological solutions continue to inspire and to provide design idea for the construction of multiscale structures with multifunctional integration.     

Flexible,Durable, and Unconditioned Superoleophobic/Superhydrophilic Surfaces for Controllable Transport and Oil–Water Separation

Superoleophobic/superhydrophilic surfaces have incomparable advantages for oil–water separation and oil droplet manipulation; however, such surfaces are difficult to obtain on the basis of surface tension theory, and existing attempts are either not fully functional or are nondurable. Here, a solution to achieve the combination of superoleophobicity and superhydrophilicity by emphasizing the polar component of surface tension is proposed. The developed surfaces can be flexibly applied to almost any solid substrate and exhibit superoleophobic and instantaneous superhydrophilic property. The surfaces applied to certain substrates can be used for controllable oil transport, oil–water separation, and emulsion demulsification. Furthermore, a novel ferroconcrete‐like structure to substantially increase the durability of the developed surfaces without affecting the superwettability is developed. The coated steel meshes preserve the ability of the material to separate oil–water mixtures even after over 400 m abrasion, which can be a significant step toward its widespread application.     

Dynamically Gas‐Phase Switchable Super(de)wetting States by Reversible Amphiphilic Functionalization: A Powerful Approach for Smart Fluid Gating Membranes

In nature, cellular membranes perform critical functions such as endocytosis and exocytosis through smart fluid gating processes mediated by nonspecific amphiphilic interactions. Despite considerable progress, artificial fluid gating membranes still rely on laborious stimuli‐responsive mechanisms and triggering systems. In this study, a room temperature gas‐phase approach is presented for dynamically switching a porous material from a superhydrophobic to a superhydrophilic wetting state and back. This is realized by the reversible attachment of bipolar amphiphiles, which promote surface wetting. Application of this reversible amphiphilic functionalization to an impermeable nanofibrous membrane induces a temporary state of superhydrophilicity resulting in its pressure‐less permeation. This mechanism allows for rapid smart fluid gating processes that can be triggered at room temperature by variations in the environment of the membrane. Owing to the universal adsorption of volatile amphiphiles on surfaces, this approach is applicable to a broad range of materials and geometries enabling facile fabrication of valve‐less flow systems, fluid‐erasable microfluidic arrays, and sophisticated microfluidic designs.     

Microskeleton‐Nanofiller Composite with Mechanical Super‐Robust Superhydrophobicity against Abrasion and Impact

Superhydrophobic surfaces have promised tremendous applications in living and industrial areas for the past two decades. Real applications, however, meet challenges, with the central concern being the robustness to resist mechanical abrasions and impacts. Here, a revolutionary strategy is proposed to create a microskeleton‐nanofiller (MSNF) film with exceptionally mechanical superstable superhydrophobicity. The strategy is conceptually different from the traditional superhydrophobic 3D microskeleton, because a 3D microskeleton is used to completely fill in the infused superhydrophobic medium. The resulting MSNF film can reserve superhydrophobicity under not only continuous abrasion before the complete wearing off the film, but also Taber abrasion, knife‐scratch, and cyclic tape peels. In addition, the MSNF film enables damage resistance to heavy impact at least up to a kinetic energy of ≈40.2 J. Furthermore, the MSNF film is also superamphiphobic to prevent oil contamination and can reserve the superhydrophobicity under large bending or torsion. Together with robustness and scalability, the MSNF film will be useful in automobiles, ships, aircraft, and houses in harsh environments and the strategy can extend to various inexpensive structured materials (such as porous iron).     

Silver‐Nanoparticle‐Colored Cotton Fabrics with Tunable Colors and Durable Antibacterial and Self‐Healing Superhydrophobic Properties

Colored cotton fabrics with satisfactory color fastness as well as durable antibacterial and self‐healing superhydrophobic properties are fabricated via a convenient solution‐dipping method that involves the sequential deposition of branched poly(ethylenimine) (PEI), silver nanoparticles (AgNPs), and fluorinated decyl polyhedral oligomeric silsesquioxane (F‐POSS) on cotton fabrics. The deposited AgNPs with tunable surface plasmon resonance endow the cotton fabrics with abundant color and and antibacterial ability. However, in general, water‐soluble AgNPs cannot be firmly deposited onto cotton fabrics to endure the laundering process. The integration of self‐healing superhydrophobicity into the cotton fabrics by depositing F‐POSS/AgNP/PEI films significantly enhances the color fastness of the AgNPs against laundry and mechanical abrasion, while retaining the antibacterial property of the AgNPs. The F‐POSS/AgNP/PEI‐coated cotton fabric accommodates an abundance of F‐POSS, which autonomically migrates to the cotton surface to repetitively restore its damaged superhydrophobicity. The self‐healing superhydrophobicity of the F‐POSS/AgNPs/PEI‐coated cotton fabric guarantees long‐term protection of the underlying AgNPs against laundry and abrasion and allows the cotton fabric to be cleaned by simple rinsing with water.     

Bioinspired Ribbed Nanoneedles with Robust Superhydrophobicity

The robustness of superhydrophobicity is a fundamental issue for the applications of water‐repellent materials. Inspired by the hierarchical structures of water‐strider legs, this work describes a new water‐repellent material decorated with ribbed, conical nanoneedles, successfully achieved on the surface of copper and consisting of copper hydroxide nanoneedle arrays sculptured with nanogrooves. The behavior of water drops on an as‐prepared surface under various external disturbances is investigated. It is shown in particular that squeezing and relaxing drops between two such surfaces leads to a fully reversible exploration of the solid surface by the liquid, which is distinct from other superhydrophobic surfaces. This unique character is attributed to the penetrating Cassie state that occurs at the ribbed, conical nanoneedles. The proprietary lateral nanogrooves can, not only vigorously support the enwrapped liquid‐air interface when a force is applied to the drop, but also provide reliable contact lines for the easy de‐pinning of the deformed interface when the force is released from the drop. The results confirm the exceptional ability of strider legs to repel water, and should help to further the design of robust water‐repellent materials and miniaturized aquatic devices.     

Ultrafast,Reversible Transition of Superwettability of Graphene Network and Controllable Underwater Oil Adhesion for Oil Microdroplet Transportation

Recently, reversible surface superwettability has attracted enormous interest, and methods to shorten the cycle time of transition have also garnered the attention of researchers. Herein, a superhydrophobic, open‐cell graphene network (OCGN) is fabricated via self‐assembly of graphene oxide and vapor ejection. Owing to the special open‐cell microstructure, the OCGNs can be transformed to be superhydrophilic rapidly within only 1 s by air plasma treatment. Moreover, the OCGNs with pure graphene composition have a high conductivity and show an ultrafast Joule heating rate of up to 20 °C s^?1 at a voltage of 20 V. By means of this property, for the first time an ultrafast recovery of the superhydrophobicity for OCGNs by self‐induced Joule heating with the shortest time of 1 min is reported. The mechanism of ultrafast, reversible transition is also explored specifically in this study. In addition, the superhydrophilic OCGNs show superoleophobicity in water and their underwater adhesion for oil droplets can be controlled by plasma treatment. Finally, the OCGNs with different oil adhesion properties are fabricated and the underwater oil microdroplet transportation is realized using OCGNs. Therefore, the OCGNs with smart surface can be an excellent candidate for achieving multifunctional superwettability of surfaces.     

Bioinspired,Stimuli‐Responsive,Multifunctional Superhydrophobic Surface with Directional Wetting,Adhesion, and Transport of Water

A novel smart stimuli responsive surface can be fabricated by the subsequent self‐assembly of the graphene monolayer and the TiO₂ nanofilm on various substrates, that is, fabrics, Si wafers, and polymer thin films. Multiscale application property can be achieved from the interfacial interaction between the hierarchical graphene/TiO₂ surface structure and the underlying substrate. The smart surface possesses superhydrophobic property as a result of its hierarchical micro‐ to nanoscale structural roughness. Upon manipulating the UV induced hydrophilic conversion of TiO₂ on graphene/TiO₂ surface, smart surface features, such as tunable adhesiveness, wettability, and directional water transport, can be easily obtained. The existence of graphene indeed enhances the electron–hole pair separation efficiency of the photo‐active TiO₂, as the time required for the TiO₂ superhydrophilic conversion is largely reduced. Multifunctional characteristics, such as gas sensing, droplet manipulation, and self‐cleaning, are achieved on the smart surface as a result of its robust superhydrophobicity, tunable wettability, and high photo‐catalytic activity. It is also revealed that the superhydrophilic conversion of TiO₂ is possibly caused by the atomic rearrangement of TiO₂ under UV radiation, as a structural transformation from {101} to {001} is observed after the UV treatment.     

A Simple Poly(Vinyl Sulfonate) Coating for All-Purpose,Self-Cleaning Applications: Molecular Packing Density–Defined Surface Superhydrophilicity

In this study, poly(vinyl sulfonate) (PVS)–capped surfaces are constructed on the polyelectrolyte multilayers (PEMs) of poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) via electrostatic assembly. The water wetting behavior on the resulting PVS-capped PEMs is meticulously correlated with the number of surface sulfonate groups with the aid of sum frequency generation spectroscopy and quartz crystal microbalance. It is found that when the molecular packing density of surface sulfonate groups is adjusted to be comparable to the maximal packing density of spheres in two dimensions (≈0.9), the PVS capping is able to effectively adsorb water molecules from the surrounding to form hydrogen-bonded networks, which not only promote complete surface wetting by water in air but also diminish surface affinity to adhesion of ice, oil and wax deposited atop. As a result, the PVS-capped PEMs are able to fulfil all the self-cleaning functions proposed for superhydrophilic surfaces including anti-fogging, anti-icing, anti-grease, anti-smudge, anti-graffiti, and anti-wax. After being coated with the self-cleaning PVS-capped PEMs, conventional stainless steel meshes are able to perform oil-water separation without prior water wetting.     

Applied Voltage and Near‐Infrared Light Enable Healing of Superhydrophobicity Loss Caused by Severe Scratches in Conductive Superhydrophobic Films

The fabrication of self‐healing/healable superhydrophobic films that can conveniently and repeatedly restore the loss of superhydrophobicity caused by severe mechanical damage, such as deep and wide surface scratches, remains challenging. In the present work, conductive superhydrophobic films that are healable by means of an applied voltage or near infrared (NIR) light irradiation are fabricated by depositing a layer of Ag nanoparticles and Ag nanowires (AgNPs‐AgNWs) on a thermally healable polycaprolactone (PCL)/poly(vinyl alcohol) (PVA) composite film, followed by the deposition of 1H,1H,2H,2H‐perfluorodecanethiol. The AgNPs‐AgNWs layer not only provides micro‐ and nanoscaled hierarchical structures in support of superhydrophobicity but also serves as an electrothermal or photothermal heater to enable healing of the underlying PCL/PVA film under the assistance of a low applied voltage or low‐power NIR light irradiation. Because of the strong adhesion between the PCL/PVA film and the AgNPs‐AgNWs layer, the healability of the PCL/PVA film is successfully conveyed to the conductive superhydrophobic layer, which can rapidly and repeatedly restore the loss of superhydrophobicity caused by cuts several hundreds of micrometers wide. The combined electrothermal and superhydrophobic properties endow the healable conductive superhydrophobic films with improved durability and usefulness as self‐cleaning, antiicing, and snow‐removing surfaces.     

Fabricating Tunable Superhydrophobic Surfaces Enabled by Surface-Initiated Emulsion Polymerization in Water

Fabricating controllable superhydrophobic surfaces remains challenging in various fields ranging from chemical industries to biomedical engineering. Conventional methods commonly require volatile organic solvents and the assistance of special surface deposition and modification equipment, which are detrimental to environment and limit their applications in micro-devices. Herein, an equipment-free method is reported to directly transform fluorinated monomer micro-droplets into hydrophobic polymer particles on flat substrate surfaces in water, simultaneously depositing hydrophobic coatings with tunable surface structures. The as-prepared surfaces show superior superhydrophobicity and great stability in extreme conditions (e.g., varying acidity, basicity, and heating conditions), and excellent anti-fouling property. Meanwhile, surface hydrophobicity can be manipulated by adjusting emulsion droplet number density and reaction time. Hence, superhydrophobic surfaces with tunable hydrophobicity gradients have been successfully fabricated in one pot. This study provides an equipment-free method to facilely fabricate controllable superhydrophobic surfaces, with great potential in the development of smart superhydrophobic materials in various engineering and industrial applications.     

Tailoring Wetting Properties at Extremes States to Obtain Antifogging Functionality

Fog formation decreases light transmission of optically clear materials. A promising approach to address this problem is to control the wetting properties of the material at extremes states, which requires imparting micro and nano morphology features on the surface. However, such features may affect the optical properties of the surface. In this work, superhydrophobic and superhydrophilic surfaces, with different morphology characteristics ranging from nanoscale to hierarchical micro-nanoscale are fabricated and evaluated in order to investigate which wetting extreme and surface morphology is more suitable to preserve the light-transmitting properties and exhibit antifogging functionalities. The performance of the aforementioned surfaces is compared for the first time in two different testing modes: under intense fog flow and no surface cooling, and under no-flow and surface cooling, which enhances dew condensation on the surfaces. It is demonstrated that superhydrophilic surfaces with nanoscale morphology maintain their optical transmittance under fog flow for more than 20 min. This duration is one of the longest reported in the literature revealing the long-term antifogging functionality of the proposed surfaces. Finally, by tailoring the morphology and the surface wetting properties, an optically switching surface (initially “milky” which becomes “clear”) when exposed to humidity is demonstrated.     

Porous Polymer Coatings: a Versatile Approach to Superhydrophobic Surfaces

Here, a facile and inexpensive approach to superhydrophobic polymer coatings is presented. The method involves the in situ polymerization of common monomers in the presence of a porogenic solvent to afford superhydrophobic surfaces with the desired combination of micro‐ and nanoscale roughness. The method is applicable to a variety of substrates and is not limited to small areas or flat surfaces. The polymerized material can be ground into a superhydrophobic powder, which, once applied to a surface, renders it superhydrophobic. The morphology of the porous polymer structure can be efficiently controlled by composition of the polymerization mixture, while surface chemistry can be adjusted by photografting. Morphology control is used to reduce the globule size of the porous architecture from micro down to nanoscale thereby affording a transparent material. The influence of both surface chemistry as well as the length scale of surface roughness on the superhydrophobicity is discussed.     

Long-Term Super-Amphiphilic Shaped-Fiber with Multi-Scale Grooved Structures: Toward Spontaneous Self-Cleaning

Despite long-term exposure to the ambient environment, fabrics made of bamboo fibers enable spontaneous self-cleaning of oil contaminants without using any surfactant. Here, it is revealed that the long-term stable super-amphiphilicity of bamboo fibers is responsible for self-cleaning behavior. Liquids of both water and oil are liable to super-spread on bamboo fibers, driven by multi-scaled capillary forces imparted by the unique shaped fibrous structures with multi-scale hierarchical ridges/grooves. Based on the minimization of free energy, the pre-wetted oils can be easily removed away by forming the water film, reaching the spontaneous self-cleaning. Notably, the super-amphiphilicity induced by the structure shows better long-term stability compared with that endowed by chemical modification. It is demonstrated that the bio-inspired artificial counterpart also exhibits excellent self-cleaning property, which inspires innovative self-cleaning textures.