Durable superhydrophobic coatings for prevention of rain attenuation of 5G/weather radomes

Design and Synthesis of a Robust and Multifunctional Superhydrophobic Coating with a Three-Dimensional Network Structure on a Paper-Based Material

A fundamental challenge in artificial superhydrophobic papers is their poor resistance to mechanical abrasion, which limits their practical application in different fields. Herein, a robust and multifunctional superhydrophobic paper is successfully fabricated via a facile spraying method by combining silver nanowires and fluorinated titania nanoparticles through a common paper sizing agent (alkyl ketene dimer) onto paper. It is shown that the surface of the paper-based material presents a three-dimensional network structure due to the cross-linking of silver nanowires with a high aspect ratio. Further hydrophilic and hydrophobic performance test results show that it exhibits exceptional water repellency, with a desirable static contact angle of 165° and roll-off angle of 6.2°. The superhydrophobic paper showcases excellent mechanical durability and maintains its superhydrophobicity even after enduring 130 linear sandpaper abrasion cycles or high-velocity water jetting impact benefited from interfacial van der Waals and hydrogen bonding. Simultaneously, the robust superhydrophobic surface can effectively prevent the penetration of acid or alkali solutions, as well as UV light, resulting in excellent chemical stability. Additionally, the superhydrophobic paper offers supplementary features such as self-cleaning, electrical conductivity, and antibacterial capability. Further development of this strategy paves a way toward next-generation superhydrophobic paper composed of nanostructures and characterized by multiple (or additional) functionalities.

Superdurable Full-Life Superhydrophobic Composite Block

Superhydrophobic materials are attractive for industrial development but plagued by poor mechanical stability. Herein, a superdurable full-life superhydrophobic composite block is designed and fabricated by embedding near-zero contractive superhydrophobic silica aerogel into a rigid iron-nickel foam structured similarly to a regular dodecahedron. The synergistic protection afforded by these materials ensures superrobust mechanical stability for the composite block, which features a high compressive strength of up to ≈7.4 MPa, and ultralow Taber abrasion of down to ≈0.567 mm after withstanding 50 000 cycles, and highly efficient water harvesting capability of up to ≈3114.3 mg min-1 cm-2 at a supercooling degree of 40 K. This robust material system provides a novel strategy to design superhydrophobic materials capable of withstanding extreme conditions, including high temperature, humidity, pressure, and abrasion.

Facile Preparation of Impalement Resistant, Mechanically Robust and Weather Resistant Photothermal Superhydrophobic Coatings for Anti-/De-icing

Photothermal superhydrophobic coatings hold great promise in addressing the limitations of conventional superhydrophobic anti-icing coatings. However, developing such coatings with excellent impalement resistance, mechanical robustness and weather resistance remains a significant challenge. Here, we report facile preparation of robust photothermal superhydrophobic coatings with all the above advantages. The coatings were prepared by spraying a dispersion consisting of fluorinated silica nanoparticles, a silicone-modified polyester adhesive and photothermal carbon black nanoparticles onto Al alloy plates followed by thermal curing. Thermal curing caused migration of perfluorodecyl polysiloxane from within the coatings to the surface, effectively maintaining a low surface energy despite the presence of the adhesive. Therefore, combined with the hierarchical micro-/nanostructure, dense yet rough nanostructure, adhesion of the adhesive and chemically inert components, the coatings exhibited remarkable superhydrophobicity, impalement resistance, mechanical robustness and weather resistance. Furthermore, the coatings demonstrated excellent photothermal effect even in the -10 °C, 80 % relative humidity and weak sunlight (0.2 sun) environment. Consequently, the coatings showed excellent passive anti-icing and active de-icing performance. Moreover, the coatings have good generalizability and scalability. We are confident that this study will accelerate the practical implementation of photothermal superhydrophobic coatings.

Fundamentals and Applications of Surface Wetting

In an era defined by an insatiable thirst for sustainable energy solutions, responsible water management, and cutting-edge lab-on-a-chip diagnostics, surface wettability plays a pivotal role in these fields. The seamless integration of fundamental research and the following demonstration of applications on these groundbreaking technologies hinges on manipulating fluid through surface wettability, significantly optimizing performance, enhancing efficiency, and advancing overall sustainability. This Review explores the behavior of liquids when they engage with engineered surfaces, delving into the far-reaching implications of these interactions in various applications. Specifically, we explore surface wetting, dissecting it into three distinctive facets. First, we delve into the fundamental principles that underpin surface wetting. Next, we navigate the intricate liquid-surface interactions, unraveling the complex interplay of various fluid dynamics, as well as heat- and mass-transport mechanisms. Finally, we report on the practical realm, where we scrutinize the myriad applications of these principles in everyday processes and real-world scenarios.

Roll-to-Roll Manufacturing of Breathable Superhydrophobic Membranes

Self-cleaning and anti-biofouling are both advantages for lotus-leaf-like superhydrophobic surfaces. Methods for creating superhydrophobicity, including chemical bonding low surface energy molecular fragments and constructing surface morphology with protrusions, micropores, and trapped micro airbags by traditional physical strategies, unfortunately, have encountered challenges. They often involve complex synthesis processes, stubborn chemical accumulation, brutal degradation, or infeasible calculation and imprecise modulation in fabricating hierarchical surface roughness. Here, a scalable method to prepare high-quality, breathable superhydrophobic membranes is proposed by developing a successive roll-to-roll laser manufacturing technique, which offers advantages over conventional fabrication approaches in enabling automatically large-scale production and ensuring cost-effectiveness. Nanosecond laser writing and femtosecond laser drilling produce surface microstructures and micropore arrays, respectively, endowing the membrane with superior antiwater capability with hierarchical microstructures forming a barrier and blocking water infiltration. The membrane's breathability is carefully optimized by tailoring micropore arrays to allow for the adequate passage of water vapor while maintaining superhydrophobicity. These membranes combine the benefits of anti-aqueous corrosive liquid behaviors, photothermal effects, thermoplastic properties, and stretchable performances as promising comprehensive materials in diverse scenes.

Attapulgite-Based Stable Superhydrophobic Coatings for Preventing Rain Attenuation of 5G Radomes

Superhydrophobic coatings hold immense promise for various applications. However, their practical use is currently hindered by issues such as poor stability, high costs, and complex preparation processes. Here, we present the preparation of cost-effective and stable superhydrophobic coatings through fluorination of natural attapulgite (F-ATP) nanorods and subsequent solvent-induced phase separation of a silicone-modified polyester adhesive (SMPA) with the F-ATP nanorods dispersed in it. Phase separation of the F-ATP/SMPA system forms a uniform suspension of microaggregates, which can be easily utilized for preparing superhydrophobic coatings via spray coating. The coatings have a low-surface-energy hierarchical micro/nanostructure due to phase separation of SMPA and adhesion of F-ATP to it. Moreover, the effects of the solvent composition (i.e., phase separation degree of SMPA) and the SMPA/F-ATP mass ratio on the morphology, superhydrophobicity, and stability of the coatings were investigated. After systematic optimization, the coatings exhibit excellent static and dynamic superhydrophobicity as well as high mechanical, chemical, thermal, and UV aging stability. Finally, the coatings were applied to the 5G radome surface and showed good rain attenuation prevention performance. Thus, we are confident that the superhydrophobic coatings have great application potential due to their advantages of outstanding performance, straightforward preparation procedures, cost-effectiveness, etc.

Large-Area Preparation of a Robust Superamphiphobic Coating for Chemical Mechanical Polishing Application

In the chemical-mechanical polishing (CMP) process, the abrasive particles in the polishing slurry tend to agglomerate easily and crystallize on the equipment surfaces during recycling, which can lead to poor wafer processing quality and additional tedious cleaning work. To overcome this issue, a simple and cost-effective self-cleaning surface preparation method has been developed. In this study, elastic and stretchable hydroxyl polydimethylsiloxane (PDMS-OH) was selected as the functional material, it was chelated with pentaerythritol tetra(3-mercapto propionate), and then 2-(perfluorooctyl)ethyl methacrylate was further grafted in situ to the polymer chains via a photoinduced thiol-ene click reaction. Hydrophobically modified micronanoscale silica particles were used to construct robust hierarchical micronanostructures while imparting stable mechanical wear resistance to the coating. The resulting superamphiphobic film exhibits the "lotus effect" and exceptional self-cleaning ability, repelling liquids such as water, hexadecane, and polishing slurry. Furthermore, the coating demonstrated outstanding chemical resistance and antifouling ability. Thus, it provides a feasible solution for preventing abrasive crystallization at critical locations where the polishing slurry flows in the CMP equipment. This work contributes to the enhanced application of superrepellent coatings in the CMP stage of semiconductor material processing.

UV-durable self-cleaning coatings for autonomous driving

A key technology to ensure the safety and accuracy of autonomous driving for future transportation is the cleanliness of the sensor surfaces for accurate signal reading. This study focuses on hydrophobic coatings with self-cleaning performances and UV durability, their possible degradation mechanism of static water contact angle (sWCA), and the effect of the hydrophobic surface on camera image quality. The UV-durable hydrophobic coatings are applied by a spray process followed by a thermal curing. The UV-durable hydrophobic coatings are evaluated on a vision camera under lab-simulated weathering conditions such as rain, mud, fog, and bugs, on samples as-prepared and after various hours of Weather-Ometer® weathering. The results indicate that the sWCA degradation of the UV-durable hydrophobic coatings during accelerated weathering is corresponding to the loss of fluorine (F) atomic percentage in the coatings, and the vision camera imaging quality improves significantly with the UV-durable hydrophobic coatings in comparison to an uncoated surface. The self-cleaning performances of the UV-durable hydrophobic coatings, as measured by two metrics using signal-to-noise ratio and modulation transfer function 50 loss (MTF50loss), linearly correlate with sWCA of the coatings. The UV-durable hydrophobic coatings on the sensor surface will significantly benefit autonomous driving specifically for accurate signal reading under inclement weather.

Pontederia crassipes inspired bottom overflow for fast and stable drainage

Fast and stable water drainage is essential for living organisms, drainage plane construction, and protection of infrastructure from damage during rainfall. Unlike traditional anti-overflow drainage methods that rely on hydrophobic or sharped edges, this study demonstrates a bottom overflow-induced drainage model inspired by the water path employed by Pontederia crassipes leaves, leading to fast and stable drainage. A superhydrophilic bottom surface guides water to overflow and pin at the bottom of a thin sheet, resulting in dripping at a higher frequency and reduced water retention. This bottom drainage idea assists large-scale thin sheets to function as efficient and stable drainage surfaces in simulated rain environments. The flexible thin sheet can also be feasibly attached to dusty substrates to effectively remove dusty rainwater with slight dust residue. The bioinspired approach presented herein suggests a promising potential for efficient water drainage on outdoor functional photovoltaic surfaces, such as solar panels and radomes, thus ensuring effective energy conversion and stable signal transmission.

A comprehensive review on anticorrosive/antifouling superhydrophobic coatings: Fabrication, assessment, applications, challenges and future perspectives

Superhydrophobicity (SHP) is an incredible phenomenon of extreme water repellency of surfaces ubiquitous in nature (E.g. lotus leaves, butterfly wings, taro leaves, mosquito eyes, water-strider legs, etc). Historically, surface exhibiting water contact angle (WCA) > 150° and contact angle hysteresis <10° is considered as SHP. The SHP surfaces garnered considerable attention in recent years due to their applications in anti-corrosion, anti-fouling, self-cleaning, oil-water separation, viscous drag reduction, anti-icing, etc. As corrosion and marine biofouling are global problems, there has been focused efforts in combating these issues using innovative environmentally friendly coatings designs taking cues from natural SHP surfaces. Over the last two decades, though significant progress has been made on the fabrication of various SHP surfaces, the practical adaptation of these surfaces for various applications is hampered, mainly because of the high cost, non-scalability, lack of simplicity, non-adaptability for a wide range of substrates, poor mechanical robustness and chemical inertness. Despite the extensive research, the exact mechanism of corrosion/anti-fouling of such coatings also remains elusive. The current focus of research in recent years has been on the development of facile, eco-friendly, cost-effective, mechanically robust chemically inert, and scalable methods to prepare durable SHP coating on a variety of surfaces. Although there are some general reviews on SHP surfaces, there is no comprehensive review focusing on SHP on metallic and alloy surfaces with corrosion-resistant and antifouling properties. This review is aimed at filling this gap. This review provides a pedagogical description with the necessary background, key concepts, genesis, classical models of superhydrophobicity, rational design of SHP, coatings characterization, testing approaches, mechanisms, and novel fabrication approaches currently being explored for anticorrosion and antifouling, both from a fundamental and practical perspective. The review also provides a summary of important experimental studies with key findings, and detailed descriptions of the evaluation of surface morphologies, chemical properties, mechanical, chemical, corrosion, and antifouling properties. The recent developments in the fabrication of SHP -Cr-Mo steel, Ti, and Al are presented, along with the latest understanding of the mechanism of anticorrosion and antifouling properties of the coating also discussed. In addition, different promising applications of SHP surfaces in diverse disciplines are discussed. The last part of the review highlights the challenges and future directions. The review is an ideal material for researchers practicing in the field of coatings and also serves as an excellent reference for freshers who intend to begin research on this topic.

Engineering an Almost All-Waterborne System for Transparent yet Superhydrophobic Surfaces with High Liquid Impalement Resistance

Realistically, green manufacturing of transparent superhydrophobic surfaces (SHSs) and high liquid impalement resistance for outdoor engineering are very necessary but pretty challenging. To address this, an almost all-waterborne system composed of synthesized partially open-cage fluorinated polyhedral oligomeric silsesquioxane bearing a pair of -OH (poc-FPOSS-2OH), silica sol, and resin precursor is engineered. The transparent SHSs facilely formed by this system are featured with the exclusive presence of wrapped silica nanoparticle (SiNP) dendritic networks at solid-gas interfaces. The wrapped SiNP dendritic networks have a small aggregation size and low distribution depth, making SHSs highly transparent. The Si-O polymeric wrappers render mechanical flexibility to SiNP dendritic networks and thus enable transparent SHSs to resist high-speed water jet impinging with a Weber number of ≥19 800 in conjunction with the extremely low-surface-energy poc-FPOSS-2OH, which is the highest liquid impalement resistance so far among waterborne SHSs, and can rival the state-of-the-art solventborne SHSs.

Impalement-Resistant, Mechanically Stable, and Anti-Static Superamphiphobic Coatings Enabled by Solvent Regulation and Their Application in Anti-Icing

Superamphiphobic coatings have good application prospects in many fields but are limited by their low impalement resistance, weak mechanical stability, and easy adhesion of tiny droplets. Here, impalement-resistant, mechanically stable, and antistatic superamphiphobic coatings were fabricated by spraying a mixture of conductive carbon black (CB), silicone-modified polyester adhesive/fluorinated SiO2 microspheres onto Al alloy. The microspheres were obtained by adhesive phase separation and the binding of fluorinated SiO2 to them. The morphology, superamphiphobicity, impalement resistance, and mechanical stability of the coatings could be regulated by using solvents with different boiling points. As a result, the coatings simultaneously exhibited outstanding mechanical stability, impalement resistance, and superamphiphobicity. The addition of conductive CB endowed the coatings with good antistatic and tiny droplet repellent properties. In addition, the coatings exhibited good anti-icing properties due to the steady air layer at the solid-liquid interface and the very small contact area between them. We suppose that the coatings are very promising for practical application in various fields, including anti-icing, due to their outstanding comprehensive properties and simple preparation process.

Polymerization of monomer aggregates for tailoring and patterning water wettability

An approach of 'polymerization of monomers in its aggregated form' is unprecedentedly introduced to (i) tailor the water wettability of fibrous and porous substrates from hydrophobicity to superhydrophobicity, and (ii) associate patterned wettability. A solution of selected monomers-i.e., alkyl acrylate in a good solvent (indicating high solubility; ethanol) was transferred into a bad solvent (refers to poor solubility; water) to achieve a stable dispersion of monomer aggregates of size <1 μm for deposition on fibrous and porous substrates. Its photopolymerization provided a durable coating with the ability to tailor the water wettability from 134° to 153°. Furthermore, a spatially selective photopolymerization process yielded a patterned interface of superhydrophilicity and superhydrophobicity. Such a facile chemical approach with the ability to provide a durable coating embedded with tailored and patterned wettability would be useful for various potential applications.

Efficient Photothermal Anti-/Deicing Enabled by 3D Cu2-x S Encapsulated Phase Change Materials Mixed Superhydrophobic Coatings

Photothermal superhydrophobic surfaces are one of the most promising anti-/deicing materials, yet they are limited by the low energy density and intermittent nature of solar energy. Here, a coupling solution based on microencapsulated phase change materials (MPCMs) that integrates photothermal effect and phase change thermal storage is proposed. Dual-shell octahedral MPCMs with Cu2 O as the first layer and 3D Cu2-x S as the second layer for the first time is designed. By morphology and phase manipulation of the Cu2-x S shell, the local surface plasmonic heating modulation of MPCMs is realized, and the MPCM reveals full-spectrum high absorption with a photothermal conversion efficiency up to 96.1%. The phase change temperature and enthalpy remain in good consistency after 200 cycles. Multifunctional photothermal phase-change superhydrophobic composite coatings are fabricated by combining the hydrolyzed and polycondensation products of octadecyl trichlorosilane and the dual-shell MPCM. The multifunctional coatings exhibit excellent anti-/deicing performance under low temperature and high humidity conditions. This work not only provides a new approach for the design of high-performance MPCMs but also opens up an avenue for the anti-icing application of photothermal phase-change superhydrophobic composite coatings.

Challenges and strategies for commercialization and widespread practical applications of superhydrophobic surfaces

Superhydrophobic (SH) surfaces have progressed rapidly in fundamental research over the past 20 years, but their practical applications lag far behind. In this perspective, we first present the findings of a survey on the current state of SH surfaces including fundamental research, patenting, and commercialization. On the basis of the survey and our experience, this perspective explores the challenges and strategies for commercialization and widespread practical applications of SH surfaces. The comprehensive performances, preparation methods, and application scenarios of SH surfaces are the major constraints. These challenges should be addressed simultaneously, and the actionable strategies are provided. We then highlight the standard test methods of the comprehensive performances including mechanical stability, impalement resistance, and weather resistance. Last, the prospects of SH surfaces in the future are discussed. We anticipate that SH surfaces may be widely commercialized and used in practical applications around the year 2035 through combination of the suggested strategies and input from both academia and industry.