Superhydrophobic surfaces by electrochemical processes

Preparation of Superhydrophobic Coating on X80 Steel and Its Corrosion Resistance in Oilfield Produced Water

Corrosion is an unavoidable issue that steel encounters during service; however, the generic methods employed for corrosion prevention often need high cost or preparation conditions. In this study, a facile chemical replacement deposition method was proposed to realize an anticorrosion superhydrophobic coating on a X80 steel surface. The growth mechanism of the rough structure and its impact on the wettability of the superhydrophobic coating were analyzed. The superhydrophobic coating, deposited for 50 s and modified for 30 min, achieved optimal electrochemical properties and a maximum water contact angle. The immersion test, in the saturated CO2 oilfield produced water, demonstrated the better corrosion resistance of superhydrophobic coating than X80 steel. Correspondingly, a kinetic corrosion model was established to analyze the anticorrosion mechanism. In summary, this method significantly improves the corrosion resistance of X80 steel and is attractive for other industrial fields.

Electrochemical Synthesis of Copper Mesh-Supported Thermo-Catalysts

Metallic substrates, widely studied in the context of monolithic catalysts, offer inherent advantages in heterogeneous catalysis due to their exceptional thermal conductivity and mechanical properties. However, synthesizing stable monolithic catalysts with metallic substrates in a well-controlled manner remains a significant challenge. Here, this work introduces a simple, cost-efficient method to fabricate robust Cu mesh-supported thermo-catalysts using a modified cycling chronopotentiometry approach, where the Cu mesh serves as a donor of Cu ions. In this method, the Cu mesh surface generates two distinct layers of CuO and Cu2O. In this context, CuO acts as the active phase, accounting for the high CO oxidation activity of Cu mesh catalysts with T90 ≈ 120 °C. Additionally, these catalysts exhibit considerable potential in electrocatalysis, showcasing significant research and application value.

Superhydrophobic Non-Metallic Surfaces with Multiscale Nano/Micro-Structure: Fabrication and Application

Multiscale nano/micro-structured surfaces with superhydrophobicity are abundantly observed in nature such as lotus leaves, rose petals and butterfly wings, where microstructures typically reinforce mechanical stability, while nanostructures predominantly govern wettability. To emulate such hierarchical structures in nature, various methods have been widely applied in the past few decades to the manufacture of multiscale structures which can be applied to functionalities ranging from anti-icing and water-oil separation to self-cleaning. In this review, we highlight recent advances in nano/micro-structured superhydrophobic surfaces, with particular focus on non-metallic materials as they are widely used in daily life due to their lightweight, abrasion resistance and ease of processing properties. This review is organized into three sections. First, fabrication methods of multiscale hierarchical structures are introduced with their strengths and weaknesses. Second, four main application areas of anti-icing, water-oil separation, anti-fog and self-cleaning are overviewed by assessing how and why multiscale structures need to be incorporated to carry out their performances. Finally, future directions and challenges for nano/micro-structured surfaces are presented.

Superhydrophobic Polyaniline-Siloxane Coatings with Excellent Barrier and Active Corrosion Protection Properties for Mild Steel

Although superhydrophobic surfaces have attracted much attention in research, their high cost, poor durability, and challenging manufacturing processes have prevented their widespread application. Here, we describe a simple method of preparing superhydrophobic polyaniline (PANI) pigments and their application in protective coatings. Doping polyaniline pigments with low surface energy perfluorodecanoic acid (PFDA) allowed them to overcome their intrinsic high surface energy, and the resultant PANI-PFDA pigments showed superhydrophobicity. The superhydrophobic PANI-PFDA pigments with different weight percentages were incorporated into a polydimethylsiloxane (PDMS) coating to prepare the superhydrophobic coating. We endeavored to examine the role that hydrophobicity played in enhancing corrosion resistance and looked into the highest concentration of pigment that the coating could withstand. Additionally, studies were carried out on the coating's adherence to the metal and the stability of hydrophobicity at various pH levels. The results showed that PANI-PFDA pigments improved the hydrophobicity and corrosion resistance in the PDMS coating without compromising its robustness and durability. Electrochemical impedance spectroscopy studies revealed that 40 wt % PANI-PFDA content in the PDMS coating provided the best corrosion protection, and this coating could offer active corrosion protection when an artificial defect was made in the coating.

Advancements in Nanoenabled Membrane Distillation for a Sustainable Water-Energy-Environment Nexus

The emergence of nano innovations in membrane distillation (MD) has garnered increasing scientific interest. This enables the exploration of state-of-the-art nano-enabled MD membranes with desirable properties, which significantly improve the efficiency and reliability of the MD process and open up opportunities for achieving a sustainable water-energy-environment (WEE) nexus. This comprehensive review provides broad coverage and in-depth analysis of recent innovations in nano-enabled MD membranes, focusing on their role in achieving desirable properties, such as strong liquid-repellence, high resistance to scaling, fouling, and wetting, as well as efficient self-heating and self-cleaning functionalities. The recent developments in nano-enhanced photothermal-catalytic applications for water-energy co-generation within a single MD system are also discussed. Furthermore, the bottlenecks are identified that impede the scale-up of nanoenhanced MD membranes and a future roadmap is proposed for their sustainable commercialiation. This holistic overview is expected to inspire future research and development efforts to fully harness the potential of nano-enabled MD membranes to achieve sustainable integration of water, energy, and the environment.

A Superhydrophobic Surface on a Superalloy Substrate with Properties of High Mechanical Strength and Self-Cleaning of Carbon Deposition

Laser processing is an efficient method for fabricating a superhydrophobic surface and has attracted much attention due to its multifunctionality. However, excessive laser processing, such as laser beam overlap and multiple scans, generates both a thick, brittle recast layer and a thin material thickness, thereby greatly reducing the mechanical strength of the substrate. In addition, there is no report on fabricating a superhydrophobic surface on a superalloy substrate whose application includes a self-cleaning property. This work proposes the fabrication of a superhydrophobic surface on a superalloy substrate with high mechanical strength by optimizing the laser processing parameters including laser power, scanning speed, line spacing, and number of scans. We found that the microstructures required by superhydrophobicity could be constructed with a single laser scan. which could guarantee a minimal loss of the mechanical strength. The fabricated superhydrophobic surface on the superalloy substrate exhibited excellent self-cleaning of carbon deposition, showing good application potential in the aero engine field.

ZrO2 Superhydrophobic Coating with an Excellent Corrosion Resistance and Stable Degradation Performance on Zr-Based Bulk Metallic Glass

Photocatalysis is an energy-saving and high-efficiency green environmental technology. Because of its wide band gap and low light utilization, few studies have been conducted on ZrO2 used as a photocatalytic material. In this paper, a corrosion-resistant superhydrophobic ZrO2 coating was prepared on the surface of Zr-based bulk metallic glass by electrochemical etching. This coating not only showed a better corrosion resistance and easier collection, but also presented a stable degradation performance when combined with H2O2; these characteristics are necessary for photocatalysts to survive under harsh environments. This study provides a new direction for designing superhydrophobic surfaces on bulk metallic glass that possess a functional performance.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

Polystyrene-Based Slippery Surfaces Enable the Generation and Easy Retrieval of Tumor Spheroids

Multicellular tumor spheroids are the most well-characterized organotypic models for cancer research. Generally, scaffold-based and scaffold-free techniques are widely used for culturing spheroids. In scaffold-free techniques, the hanging drop (HD) method is a more versatile technique, but the retrieval of three-dimensional (3D) cell spheroids in the hanging drop method is usually labor-intensive. We developed oil-coated polystyrene nanofiber-based reusable slippery surfaces for the generation and easy retrieval of 3D spheroids. The developed slippery surfaces facilitated the rolling and gliding of the cell medium drops as well as holding the hydrophilic drops for more than 72 h by the virtue of surface tension as in the hanging drop method. In this study, polystyrene nanofibers were developed by the facile technique of electrospinning and the morphological evaluation was performed by scanning electron microscopy (SEM) and cryo-FESEM. We modeled the retrieval process of 3D spheroids with the ingredients of 3D spheroid generation, such as water, cell culture media, collagen, and hyaluronic acid solution, demonstrating the faster and easy retrieval of 3D spheroids within a few seconds. We created MCF-7 spheroids as a proof of concept with a developed slippery surface. 3D spheroids were characterized for their size, homogeneity, reactive oxygen species, proliferative marker (Ki-67), and hypoxic inducing factor 1ά (HIF-1ά). These 3D tumor spheroids were further tested for evaluating the cellular toxicity of the doxorubicin drug. Hence, the proposed slippery surfaces demonstrated the potential alternative of culturing 3D tumor spheroids with an easy retrieval process with intact 3D spheroids.

Self-assembled fatty acid crystalline coatings display superhydrophobic antimicrobial properties

Superhydrophobicity is a well-known wetting phenomenon found in numerous plants and insects. It is achieved by the combination of the surface's chemical properties and its surface roughness. Inspired by nature, numerous synthetic superhydrophobic surfaces have been developed for various applications. Designated surface coating is one of the fabrication routes to achieve the superhydrophobicity. Yet, many of these coatings, such as fluorine-based formulations, may pose severe health and environmental risks, limiting their applicability. Herein, we present a new family of superhydrophobic coatings comprised of natural saturated fatty acids, which are not only a part of our daily diet, but can be produced from renewable feedstock, providing a safe and sustainable alternative to the existing state-of-the-art. These crystalline coatings are readily fabricated via single-step deposition routes, namely thermal deposition or spray-coating. The fatty acids self-assemble into highly hierarchical crystalline structures exhibiting a water contact angle of ∼165° and contact angle hysteresis lower than 6°, while their properties and morphology depend on the specific fatty acid used as well as on the deposition technique. Moreover, the fatty acid coatings demonstrate excellent thermal stability. Importantly, this new family of coatings displays excellent anti-biofouling and antimicrobial properties against Escherichia coli and Listeria innocua, used as relevant model Gram-negative and Gram-positive bacteria, respectively. These multifunctional coatings hold immense potential for application in numerous fields, ranging from food safety to biomedicine, offering sustainable and safe solutions.

Special Superwetting Materials from Bioinspired to Intelligent Surface for On-Demand Oil/Water Separation: A Comprehensive Review

Since superwetting surfaces have emerged, on-demand oil/water separation materials serve as a new direction for meeting practical needs. This new separation mode uses a single porous material to allow oil-removing and water-removing to be achieved alternately. In this review, the fundamentals of wettability are systematically summarized in oil/water separation. Most importantly, the two states, bioinspired surface and intelligent surface, are summarized for on-demand oil/water separation. Specifically, bioinspired surfaces include micro/nanostructures, bioinspired chemistry, Janus-featured surfaces, and dual-superlyophobic surfaces that these superwetting materials can possess asymmetric wettability in one structure system or opposite underliquid wettability by prewetting. Furthermore, an intelligent surface can be adopted by various triggers such as pH, thermal and photo stimuli, etc., to control wettability for switchable oil/water separation reversibly, expressing a thought beyond nature to realize innovative oil/water separation by external stimuli. Remarkably, this review also discusses the advantages of all the materials mentioned above, expanding the separation scope from the on-demand oil/water mixtures to the multiphase immiscible liquid-liquid mixtures. Finally, the prospects of on-demand oil/water separation materials are also concluded.

Advances in the Fabrication and Characterization of Superhydrophobic Surfaces Inspired by the Lotus Leaf

Nature has proven to be a valuable resource in inspiring the development of novel technologies. The field of biomimetics emerged centuries ago as scientists sought to understand the fundamental science behind the extraordinary properties of organisms in nature and applied the new science to mimic a desired property using various materials. Through evolution, living organisms have developed specialized surface coatings and chemistries with extraordinary properties such as the superhydrophobicity, which has been exploited to maintain structural integrity and for survival in harsh environments. The Lotus leaf is one of many examples which has inspired the fabrication of superhydrophobic surfaces. In this review, the fundamental science, supported by rigorous derivations from a thermodynamic perspective, is presented to explain the origin of superhydrophobicity. Based on theory, the interplay between surface morphology and chemistry is shown to influence surface wetting properties of materials. Various fabrication techniques to create superhydrophobic surfaces are also presented along with the corresponding advantages and/or disadvantages. Recent advances in the characterization techniques used to quantify the superhydrophobicity of surfaces is presented with respect to accuracy and sensitivity of the measurements. Challenges associated with the fabrication and characterization of superhydrophobic surfaces are also discussed.

Effects of Adsorbate Diffusion and Edges in a Transition from Particle to Dendritic Morphology during Silver Electrodeposition

During silver electrodeposition on Au nanoparticle (NP)-covered highly oriented pyrolitic graphite, a transition from an initial growth of microsized particles to the growth of dendrites with pine tree shape (nanotrees) is observed, which is an advancement for material growth with hierarchical surface roughness. Using kinetic Monte Carlo simulations of an electrodeposition model, those results are explained by the interplay of diffusive cation flux in the electrolyte and relaxation of adsorbed atoms by diffusion on quenched crystal surfaces. First, simulations on NP-patterned substrates show the initial growth of faceted silver particles, followed by the growth of nanotrees with shapes similar to the experiments. Next, simulations on electrodes with large prebuilt particles explain the preferential nanotree growth at corners and edges as a tip effect. Simulations on wide flat electrodes relate the nanotree width with two model parameters describing surface diffusion of silver atoms: maximal number of random hops (G) and probability of hop per neighbor (P). Finally, simulations with small electrode seeds confirm the transition from initially compact particles to the nucleation of nanotrees and provide estimates of the transition sizes as a function of those parameters. The simulated compact and dendritic deposits show dominant (111) surface orientation, as observed in experiments. Extrapolations of simulation results to match microparticle and nanotree sizes lead to G = 4 × 10¹¹ and P = 0.03, suggesting to interpret those sizes as diffusion lengths on the growing surfaces and giving diffusion coefficients 2 to 3 × 10^-13 m²/s for deposited silver atoms. These results may motivate studies to relate diffusion coefficients with atomic-scale interactions.

Dynamic Electrolyte Spreading during Meniscus-Confined Electrodeposition and Electrodissolution of Copper for Surface Patterning

Meniscus-confined electrodeposition and electrodissolution are a facile maskless approach to generate controlled surface patterns and 3D microstructures. In these processes, the solid-liquid interfacial area confined by the meniscus dictates the zone on which the electrodeposition or the electrodissolution occurs. In this work, we show that the process of electrodeposition or electrodissolution in a meniscus-confined droplet system can lead to dynamic spreading of the meniscus, thereby changing the solid-liquid interfacial area confined by the meniscus. Our results show that the wetting dynamics depends on the applied voltage and the type of interface underneath the droplet, specifically a smooth surface with a homogeneous solid-liquid interface or a superhydrophobic surface with a heterogeneous solid-liquid and liquid-vapor interface. It is found that both electrodissolution and electrodeposition processes induced droplet spreading in the case of a smooth surface with a homogeneous interface. However, a superhydrophobic surface with a heterogeneous interface under the droplet produced nonlinear spreading during electrodissolution and spreading inhibition during electrodeposition. The underlying mechanisms resulting in the observed behavior have been explicated. The dynamic droplet spreading could modify the dimensions of the patterns formed and hence is of immense importance to the meniscus-confined electrochemical micromachining. The findings also provide fundamental insights into the spreading behavior and wetting transitions induced by electrochemical reactions.

Heat Stability and Icing Delay on Superhydrophobic Coatings in Facile One Step

Superhydrophobic coatings are limited to poor durability and a tedious preparation process. In this work, an efficient, eco-friendly, and cost-effective sol-gel method is developed for preparing superhydrophobic surfaces using an all-in-one suspension composed of methyltrimethoxysilane (MTMS), nano silicon dioxide (SiO₂) particles, and micron zinc oxide (ZnO) particles. Superhydrophobic coatings with a contact angle (CA) up to 153.9° and a sliding angle (SA) of about 3.0° are prepared on Q235 steel substrates using MTMS 5 mL, 0.8 g of nano SiO₂, and 0.2 g of micron ZnO. The morphology of the superhydrophobic coating is characterized by scanning electron microscopy (SEM), and the surface is covered with a micro- and nano-scaled hierarchical rough structure. A series of tests are conducted, including long-term stability tests and thermostability tests. The CAs are all above 150°, and the SAs are below 6.3°, indicating the excellent static stability of the prepared superhydrophobic coatings. Moreover, the CA of the superhydrophobic coating remains above 152° after 120 h of UV exposure, and the time for a water droplet to freeze on the surface of the superhydrophobic coating is 18 times of the bare Q235 steel, indicating that the superhydrophobic coating exhibits good resistance to UV radiation and icing-delay properties.

Facile and Eco-Friendly Preparation of Mild Steel Based Superhydrophobic Surfaces without Chemical Modifications

The fabrication of superhydrophobic coatings on mild steel has attracted considerable attention. However, some methods are cumbersome and unsuitable for large-scale preparation, limiting industrial applications. Furthermore, the extensive use of fluorinated compounds to achieve low surface energy is not environmentally friendly. This paper proposed a facile method based on electrodeposition and annealing to prepare mild steel-based superhydrophobic surfaces without chemical modifications. Subsequently, SEM images were analyzed, and it was observed that the plating parameter (current and time) significantly affected surface morphology. At optimum process parameters, a rough surface with a multi-level structure was formed on the plated surface, contributing to superhydrophobic properties. XPS, EDS, and XRD were utilized to analyze surface composition. The results indicated the presence of copper oxides, zinc oxides, and a large number of hydrocarbons on the prepared superhydrophobic surface. These transition metal oxides on the surface adsorbed hydrocarbons in the air during the annealing process, which lowered the surface energy. Combined with the obtained multi-level morphology, a superhydrophobic surface was achieved. Finally, the corrosion behavior was evaluated in 3.5 wt% NaCl solution by AC impedance spectroscopy. Results showed that the obtained superhydrophobic surface, compared with the untreated coating and the steel substrate, showed a substantial improvement in corrosion resistance. A mild steel-based superhydrophobic surface with a contact angle greater than 150 degrees and excellent corrosion resistance was finally obtained. We hope this study will facilitate the industrial preparation of superhydrophobic coatings, especially in marine engineering, since this method does not require complex processes or expensive equipment and does not require fluorinated substances.

Bioinspired Robust Water Repellency in High Humidity by Micro-meter-Scaled Conical Fibers: Toward a Long-Time Underwater Aerobic Reaction

Superhydrophobic surfaces have suffered from being frequently penetrated by micro-/nano-droplets in high humidity, which severely deteriorates their water repellency. So far, various biological models for the high water repellency have been reported, which, however, focused mostly on the structural topology with less attention on the dimension character. Here, we revealed a common dimension character of the superhydrophobic fibrous structures of both Gerris legs and Argyroneta abdomens, featured as the conical topology and the micro-meter-scaled cylindrical diameter. In particular, it can be expressed by using a parameter of rp/l > 0.75 μm (r, l, and p are the radius, length, and apex spacing between fibers, respectively). Drawing inspiration, we developed a superhydrophobic micro-meter-scaled conical fiber array with a rather high rp/l value of 0.85 μm, which endows ultra-high water repellency even in high humidity. The micro-meter-scale asymmetric confined space between fibers enables generating a big difference in the Laplace pressure enough to propel the condensed dews away, while the tips help pin the air pocket underwater with a rather long life over 41 days. Taking advantage, we demonstrated a sustainable underwater aerobic reaction where oxygen was continuously supplied from the trapped air pocket by a gradually diffusing process. As a parameter describing both the dimension character and structural topology, the rp/l offers a new perspective for fabricating superhydrophobic fibrous materials with robust water repellency in high humidity, which inspires the innovative underwater devices with a robust anti-wetting performance.

Fabrication of hydrophobic PLA filaments for additive manufacturing

There is an ever-greater need for self-cleaning and water-repelling properties of hydrophobic materials at this time in history, mainly due to the coronavirus disease 2019 (COVID-19) pandemic. However, the fabrication processes used to create hydrophobic materials are typically time-consuming and costly. Thus, this study aims to create hydrophobic materials based on low-cost manufacturing. In this study, polylactic acid (PLA) was mixed with various concentrations of hexadecyltrimethoxysilane (HDTMS) and polytetrafluoroethylene (PTFE) with the aid of solvents, chloroform, and acetone, through the solvent casting and melt extrusion process, which is capable of producing hydrophobic PLA filaments suitable for additive manufacturing (AM). Water contact angle (WCA) measurements were performed to verify the improved hydrophobicity of PLA/HDTMS/PTFE filaments. According to the results, it was discovered that the best filament WCAs were achieved with 2 g (10 wt%) of PLA, 0.2 ml of HDTMS, and 1 ml of PTFE (2 g PLA + 0.2 ml HDTMS + 1 ml PTFE), producing an average WCA of 131.6° and the highest WCA of 132.7°. These results indicate that adding HDTMS and PTFE to PLA significantly enhances filament hydrophobicity. Additionally, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) techniques were utilized to characterize the surface morphology, molecular interactions, and thermal decompositions of the prepared PLA/HDTMS/PTFE filaments. This study revealed that compared to 2 g of pure PLA filament, HDTMS and PTFE altered the microstructure of the filament. Its thermal degradation temperature was impacted, but the melting temperature was not. Therefore, the PLA/HDTMS/PTFE filament is good enough to be printed by the fused filament fabrication (FFF) AM process.

Long-Term Durability of Robust Super-Hydrophobic Co–Ni-Based Coatings Produced by Electrochemical Deposition

The long-term durability for two kinds of Co–Ni-based robust coatings, the Co–Ni super-hydrophobic (Co–Ni SHPB) coating and Co–Ni/WC super-hydrophobic (Co–Ni/WC SHPB) coating, was analyzed through an immersion test in 3.5 wt.% NaCl solution. The evolution of their surface properties was characterized by scanning electron microscope (SEM) images, energy-dispersive spectrometry (EDS), a wettability measurement and X-ray photoelectron spectrometer (XPS), and the evolution of anti-corrosion mechanisms was evaluated with electrochemical measurements. The results show that as-prepared two kinds of robust coatings display a good long-term durability, with the Co–Ni SHPB coating and Co–Ni/WC SHPB coating losing their super-hydrophobicity after being immersed for more than 10 days. Additionally, both kinds of coatings present efficient corrosion protection even after long-term immersion.

Robust and durable liquid-repellent surfaces

This review provides a comprehensive summary of characterization, design, fabrication, and application of robust and durable liquid-repellent surfaces.

One-step fabrication of soft calcium superhydrophobic surfaces by a simple electrodeposition process

A simple, one-step electrodeposition process was rapidly performed on a metal substrate to fabricate calcium superhydrophobic surfaces in an electrolyte containing calcium chloride (CaCl₂), myristic acid (CH₃(CH₂)₁₂COOH), and ethanol, which can avoid the intricate post-processing of surface treatment. The morphology and surface chemical compositions of the fabricated superhydrophobic surfaces were systematically examined by means of SEM, XRD, and FTIR, respectively. The results indicate that the deposited surfaces were mainly composed of calcium myristate, which can dramatically lower surface free energy. The shortest process for constructing a superhydrophobic surface is about 0.5 min, and the maximum contact angle of the as-prepared surfaces can reach as high as 166°, showing excellent superhydrophobicity. By adjusting the electrodeposition time, the structure of the cathodic surface transforms from the turfgrass structure, loose flower structures, larger and dense flower structures, secondary flower structures, and then into tertiary or more flower structures. The superhydrophobic surfaces showed excellent rebound performance with a high-speed camera. After a pressing force, their hardness increases, but the superhydrophobic performance is not weakened. Inversely, the bouncing performance is enhanced. This electrodeposition process offers a promising approach for large areas of superhydrophobic surfaces on conductive metals and strongly impacts the dynamics of water droplets.

We investigated a one-step method for calcium superhydrophobic surface preparation and researched the formation process of loose, flower-like microstructures. Also, we found that the pressing force strongly impacts the dynamics of water droplets.

Anticorrosion Behaviour of SS304 Microgroove Surfaces in Saline Water

The 304 Stainless Steel (SS304) is severely affected by salt water corrosion due to its high surface wettability. By reducing its surface wettability, its corrosion can be reduced. To achieve this, topographical modification of the steel surface is an effective route. In this work, SS304 flat surfaces were topographically modified into microgrooves (ridge width 250 μm to 500 μm, groove width 200 μm, width ratio = ridge width/groove width >1). Wire cut electrical discharge machining was used to fabricate the microgrooves. Long-term wetting characteristics and long-term corrosion behaviour of flat surface and microgrooves were studied. The influence of the nature of wetting of the tested surfaces on their corrosion behaviour was examined. The sessile drop method and potentiodynamic polarization tests in sodium chloride (3.5 wt. % NaCl) solution (intermittent and continuous exposures for 168 h) were studied to characterize their wetting and corrosion behaviours, respectively. Topographical modification imparted long-term hydrophobicity and, as a consequence, long-term anticorrosion ability of the steel surface. Micropatterning reduced the corrosion rate by two orders of magnitude due to reduction in interfacial contact area with the corrosive fluid via composite wetting, i.e., solid–liquid–air interface. Microgrooves showed corrosion inhibition efficiency ≥88%, upon long-term exposure to NaCl solution. By comparing the wetting and corrosion behaviours of the microgrooves with those of the previously studied microgrooves (ridge width/groove width <1), it was found that the surface roughness of their ridges strongly influences their wetting and corrosion properties.

Metal Oxide-Related Dendritic Structures: Self-Assembly and Applications for Sensor, Catalysis, Energy Conversion and Beyond

In the past two decades, we have learned a great deal about self-assembly of dendritic metal oxide structures, partially inspired by the nanostructures mimicking the aesthetic hierarchical structures of ferns and corals. The self-assembly process involves either anisotropic polycondensation or molecular recognition mechanisms. The major driving force for research in this field is due to the wide variety of applications in addition to the unique structures and properties of these dendritic nanostructures. Our purpose of this minireview is twofold: (1) to showcase what we have learned so far about how the self-assembly process occurs; and (2) to encourage people to use this type of material for drug delivery, renewable energy conversion and storage, biomaterials, and electronic noses.

A Review of Fabrication Methods, Properties and Applications of Superhydrophobic Metals

Hydrophobicity and superhydrophobicity with self-cleaning properties are well-known characteristics of several natural surfaces, such as the leaves of the sacred lotus plant (Nelumbo nucifera). To achieve a superhydrophobic state, micro- and nanometer scale topography should be realized on a low surface energy material, or a low surface energy coating should be deposited on top of the micro-nano topography if the material is inherently hydrophilic. Tailoring the surface chemistry and topography to control the wetting properties between extreme wetting states enables a palette of functionalities, such as self-cleaning, antifogging, anti-biofouling etc. A variety of surface topographies have been realized in polymers, ceramics, and metals. Metallic surfaces are particularly important in several engineering applications (e.g., naval, aircrafts, buildings, automobile) and their transformation to superhydrophobic can provide additional functionalities, such as corrosion protection, drag reduction, and anti-icing properties. This review paper focuses on the recent advances on superhydrophobic metals and alloys which can be applicable in real life applications and aims to provide an overview of the most promising methods to achieve sustainable superhydrophobicity.

Bioinspired wettable-nonwettable micropatterns for emerging applications

Superhydrophilic and superhydrophobic surfaces are prevalent in nature and have received tremendous attention due to their importance in both fundamental research and practical applications. With the high interdisciplinary research and great development of microfabrication techniques, artificial wettable-nonwettable micropatterns inspired by the water-collection behavior of desert beetles have been successfully fabricated. A combination of the two extreme states of superhydrophilicity and superhydrophobicity on the same surface precisely, wettable-nonwettable micropatterns possess unique functionalities, such as controllable superwetting, anisotropic wetting, oriented adhesion, and other properties. In this review, we briefly describe the methods for fabricating wettable-nonwettable patterns, including self-assembly, electrodeposition, inkjet printing, and photolithography. We also highlight some of the emerging applications such as water collection, controllable bioadhesion, cell arrays, microreactors, printing techniques, and biosensors combined with various detection methods. Finally, the current challenges and prospects of this renascent and rapidly developing field are proposed and discussed.

Electrophoretic-deposited Superhydrophobic Coatings

Electrophoretic deposition (EPD) is an excellent surface coating approach widely investigated for applications ranging from solar cells, batteries, electrochemical capacitors, solid oxide fuel cells, sensors, molecular sieves, corrosion-resistant coatings, and biomedical materials. On the other hand, superhydrophobic (SHPC) surfaces have enticed substantial recent research interest owing to their superb surface properties. Here, we provide a comprehensive review of electrophoretic-deposited SHPC coatings. Concise descriptions of EPD and superhydrophobicity are provided first, followed by a brief mentioning of works reported on electrophoretic-deposited SHPC coatings by one-step or two-step processing (§2.1). The next section (§2.2) delivers a comprehensive description of these reports based on the micro/nanoparticles used. Works reported in specific applications such as anti-corrosion, biomedical, and oil-separation are described in §2.3. Future scopes of research also presented.

One-step fabrication of robust and durable superamphiphobic, self-cleaning surface for outdoor and in situ application on building substrates

HYPOTHESIS

Water and oil inhibition treatment is essential for protecting natural and artificial stone surfaces. Bioinspired super-antiwetting surfaces with "lotus effect", together with superoleophobic properties, can be achieved combining very low-surface-energy materials and suitable surface roughness. Exploiting the natural roughness of stone surfaces, the simple and inexpensive fabrication of superamphiphobic surfaces through the coating dispersion deposition is expected. It seems the ideal method for the safeguard of contemporary and historical constructions, since the physical, chemical and aesthetic properties can be maintained.

EXPERIMENTS

The new coating agent (3-perfluroether-amidopropylsilane) was synthesized via one-step amidation. Hydrophobicity, robustness and environmental durability were systematically studied on stone surfaces through several tests: contact angle (CA), contact angle hysteresis (CAH), water inhibition efficiency, vapor diffusivity, chemical and mechanical resistance, artificial and field-exposure ageing.

FINDINGS

The as-prepared coating demonstrated superamphiphobicity (oil and water CA > 150° with CAH < 10°) on stones with low and high porosity. Moreover, it manifested very high water inhibition efficacy while maintaining high vapor diffusivity and aesthetic properties of substrates. The superhydrophobic coating showed good robustness towards corrosive chemical agents, peeling, mechanical abrasion, water immersion and environmental weathering, thereby permitting various outdoor applications, including stone protection in rainy regions where acid rain is also present.

The effects of bio-inspired micro/nano scale structures on anti-icing properties

Ice formation and accumulation have detrimental effects on commercial surfaces and people's lives. The ice adhesion strength decreases with increasing surface hydrophobicity, and the superhydrophobicity of a surface can be constructed by a combination of low surface free energy and high surface roughness. Conversely, the characteristics of biological surfaces have aroused wide attention as a result of the superhydrophobicity of plants and animals, deriving from the synergistic effects of chemical compositions and multi-scale hierarchical structures. Therefore, inspired by bio-mimetic studies on biological surfaces, a lot of artificial bio-inspired superhydrophobic surfaces have been broadly designed and constructed. Herein, we aim to summarize the fundamental theories of surface wettability and recent progress in the fabrication of bio-inspired surfaces. The bio-inspired surfaces prepared by different facile methods not only have superhydrophobicity, but also have anti-icing/icephobic properties. In the end, some challenges and problems in the future study and advancement of bio-inspired superhydrophobic surfaces are proposed.

Crystal face dependent intrinsic wettability of metal oxide surfaces

Knowledge of intrinsic wettability at solid/liquid interfaces at the molecular level perspective is significant in understanding crucial progress in some fields, such as electrochemistry, molecular biology and earth science. It is generally believed that surface wettability is determined by the surface chemical component and surface topography. However, when taking molecular structures and interactions into consideration, many intriguing phenomena would enrich or even redress our understanding of surface wettability. From the perspective of interfacial water molecule structures, here, we discovered that the intrinsic wettability of crystal metal oxide is not only dependent on the chemical components but also critically dependent on the crystal faces. For example, the [Formula: see text] crystal face of α-Al2O3 is intrinsically hydrophobic with a water contact angle near 90°, while another three crystal faces are intrinsically hydrophilic with water contact angles <65°. Based on surface energy analysis, it is found that the total surface energy, polar component and Lewis base portion of the hydrophobic crystal face are all smaller than the other three hydrophilic crystal faces indicating that they have different surface states. DFT simulation further revealed that the adsorbed interfacial water molecules on each crystal face hold various orientations. Herein, the third crucial factor for surface wettability from the perspective of the molecular level is presented, that is the orientations of adsorbed interfacial water molecules apart from the macro-level chemical component and surface topography. This study may serve as a source of inspiration for improving wetting theoretical models and designing controllable wettability at the molecular/atomic level.

Study of Cement-Based Superhydrophobic Composite Coating: New Option for Water Drainage Pipeline Rehabilitation

A great number of urban underground concrete water drainage systems in China are facing challenges of corrosion, blockage, and leakage. This could result in engineering accidents such as urban inland inundation, pipeline collapse, leakage, and blockage. The common contributing factors for pipeline leakage and blockage are the porous structures and the perishable surfaces of concrete pipes. To address these issues, we synthesized superhydrophobic coating materials such as SiO₂ aerosol, bisphenol A diglycidyl ether (DGEBA), and N-β-aminoethyl-γ-aminopropyltrimethoxysilane (AEAPTS). Our superhydrophobic coating on cement-based surfaces presents good waterproof ability, mechanical stability, and self-cleaning properties. Test results show that the superhydrophobic coating exhibits higher water discharge capacity and survivability to corrosive underground water drainage pipeline environments. Hence, this SiO₂ aerosol @ bisphenol A diglycidyl ether coating possesses enormous potential in surface modification of pipeline rehabilitation materials.

Superhydrophobic surfaces and coatings by electrochemical anodic oxidation and plasma electrolytic oxidation

The review provides a comprehensive account of superhydrophobic surfaces fabricated by electrochemical anodic oxidation (anodization). First, reported works on superhydrophobic polymers and metals made by using anodized metal oxide porous templates as moulds are presented (section 2). The next section provides a detailed description of the different fabrication approaches of superhydrophobic surfaces on anodized metallic substrates (section 3.1). The published information on superhydrophobic anodized surfaces in various applications, viz. anti-corrosion, anti-icing, oil separation, and biomedical are systematically covered (section 3.2). Superhydrophobic surfaces fabricated by plasma electrolytic oxidation are also presented (section 4). Future research perspectives debated. The collective information provided is helpful to further advance R & D in making pioneering superhydrophobic anodized nanoporous surfaces.

Underwater writable and heat-insulated paper with robust fluorine-free superhydrophobic coatings

Since its invention invented in China, paper has been widely used in the world for quite a long time. However, some intrinsic defects servely hinder its application in some extreme conditions, such as underwater or in fire. Herein, a bio-inspired durable paper with robust fluorine-free coatings was fabricated via a two-step spray-deposition technique. It not only consisted of modified SiO₂ microspheres and nanoparticles, but also contained an epoxy resin, endowing the paper with multifunctional properties. First, this bio-inspired functional paper showed excellent superhydrophobic and self-cleaning properties with a high static water contact angle (WCA) of 162.7 ± 0.5° and a low sliding angle (SA) of 5.7 ± 0.6°. Moreover, it possessed unusual repellent properties toward multiple aqueous-based liquids and heat-insulated properties. Second, this paper could be used for writing underwater and maintained satisfactory superhydrophobic performance for a long time with a WCA of 153.3 ± 1.8°. Besides, its high mechanical robustness was also experimentally confirmed in harsh working conditions, such as strong acid/alkali, boiling water, abrasion, bending, and folding. Compared with conventional paper, it is anticipated that this bio-inspired functional paper would be really competitive and demonstrate great potential in the field of underwater and fire-proof applications.

Electrodeposition of (hydro)oxides for an oxygen evolution electrode

Electrochemical water splitting is a promising technology for hydrogen production and sustainable energy conversion, but the electrolyzers that are currently available do not have anodic electrodes that are robust enough and highly active for the oxygen evolution reaction (OER). Electrodeposition provides a feasible route for preparing freestanding OER electrodes with high active site utilization, fast mass transport and a simple fabrication process, which is highly attractive from both academic and commercial points of view. This minireview focuses on the recent electrodeposition strategies for metal (hydro)oxide design and water oxidation applications. First, the intrinsic advantages of electrodeposition in comparison with traditional technologies are introduced. Then, the unique properties and underlying principles of electrodeposited metal (hydro)oxides in the OER are unveiled. In parallel, illustrative examples of the latest advances in materials structural design, controllable synthesis, and mechanism understanding through the electrochemical synthesis of (hydro)oxides are presented. Finally, the latest representative OER mechanism and electrodeposition routes for OER catalysts are briefly overviewed. Such observations provide new insights into freestanding (hydro)oxides electrodes prepared via electrodeposition, which show significant practical application potential in water splitting devices. We hope that this review will provide inspiration for researchers and stimulate the development of water splitting technology.

Current Status and Future Prospects of Applying Bioinspired Superhydrophobic Materials for Conservation of Stone Artworks

The development of innovative materials is one of the most important focus areas in heritage conservation research. Eligible materials can not only protect the physical and chemical integrity of artworks but also preserve their artistic and aesthetic features. Recently, as one of the hot research topics in materials science, biomimetic superhydrophobic materials have gradually attracted the attention of conservation scientists due to their unique properties. In fact, ultra-repellent materials are particularly suitable for hydrophobization treatments on outdoor artworks. Owing to their excellent hydrophobicity, superhydrophobic materials can effectively prevent the absorption and penetration of liquid water as well as the condensation of water vapor, thus greatly relieving water-induced decay phenomena. Moreover, in the presence of liquid water, the superhydrophobic surfaces equipped with a self-cleaning property can clean the dirt and dust deposited spontaneously, thereby restoring the artistic features simultaneously. In the present paper, besides the basic principles of wetting on solid surfaces, materials, and methods reported for preparing bioinspired ultra-repellent materials, the recently proposed materials for art conservation are also introduced and critically reviewed, along with a discussion on the droplet impact and durability of the artificial superhydrophobic surfaces. Lastly, the current status and the problems encountered in practical application are also pointed out, and the focus of future research is presented as well.

Micro-/Nanostructured Interface for Liquid Manipulation and Its Applications

Understanding the relationship between liquid manipulation and micro-/nanostructured interfaces has gained much attention due to the wide potential applications in many fields, such as chemical and biomedical assays, environmental protection, industry, and even daily life. Much work has been done to construct various materials with interfacial liquid manipulation abilities, leading to a range of interesting applications. Herein, different fabrication methods from the top-down approach to the bottom-up approach and subsequent surface modifications of micro-/nanostructured interfaces are first introduced. Then, interactions between the surface and liquid, including liquid wetting, liquid transportation, and a number of corresponding models, together with the definition of hydrophilic/hydrophobic, oleophilic/olephobic, the definition and mechanism of superwetting, including superhydrophobicity, superhydrophilicity, and superoleophobicity, are presented. The micro-/nanostructured interface, with major applications in self-cleaning, antifogging, anti-icing, anticorrosion, drag-reduction, oil-water separation, water collection, droplet (micro)array, and surface-directed liquid transport, is summarized, and the mechanisms underlying each application are discussed. Finally, the remaining challenges and future perspectives in this area are included.