Thermal Processing of Silicones for Green, Scalable, and Healable Superhydrophobic Coatings

In situ fabrication of porous polymer films embedded with perovskite nanocrystals for flexible superhydrophobic piezoresistive sensors

The application of pressure sensors based on perovskite in high-humidity environments is limited by the effect of water on their stability. Endowing sensors with superhydrophobicity is an effective strategy to overcome the issue. In this work, MAPbBr3/Polyvinylidene Fluoride-TFSI composite was prepared by a one-step in-situ strategy to form a flexible superhydrophobic pressure sensor, which exhibited a contact angle of 150.25°. The obtained sensor exhibited a sensitivity of 0.916 in 1 kPa, a detection limit of 0.2 Pa, a precision of 0.1 Pa, and a response/recovery of ∼100 ms, along with good thermal stability. Through density functional theory calculations, it is revealed that the formation of the porosity is attributed to the interaction between the polymer and EMIM TFSI, which further leads to superhydrophobicity. And, the perovskite structure is easy to change under pressure, affecting the carrier transport and electrical signals output, which explains the sensing mechanism. In addition, the sensor performed well in monitoring facial expression, pulse, respiration, finger bending, and wind speed ranging from 1 m/s to 6 m/s. With both the Linear Regression and the Random Forest algorithm, the sensor can monitor the wind speed with an R2 greater than 0.977 in 60 tests.

Sustainable Manufacturing of Multifunctional Fluorine-Free Superslippery Flexible Surfaces

Surface contamination and friction result in significant energy losses with widespread environmental impact. In the present work, we developed fluorine-free super-slippery surfaces employing environmentally friendly and simple biofuel-based flame treatment of polydimethylsiloxane (PDMS). Through a unique combination of processing parameters, highly transparent (>90%) and flexible films were engineered with omniphobic, anti-icing, and ultra-low friction properties. The processed films showed an extremely low tilting angle (<5°) and contact angle hysteresis (<4°) against different liquids, even under subzero temperatures. The coefficient of friction (COF) reduced to 0.01 after processing compared to ∼1 for PDMS. Extremely low ice adhesion of <20 kPa and enhanced freezing time ensured anti-icing behavior. The exceptional multidimensional traits were derived from the extremely stable silicone lubricant layer ensured by the hierarchically structured wrinkles. Wind tunnel tests showed that an air drag velocity of less than 0.5 m/s was sufficient to initiate droplet motion, highlighting low interfacial friction that leads to an anti-staining nature. Sustaining the self-cleaning and anti-staining characteristics, the processed surface showed utmost durability under different harsh conditions. The super-slippery surfaces with multifunctional characteristics fabricated through a sustainable route can be effectively used for various engineering and industrial applications.

Towards Sustainability: An Eco-Friendly Approach for Durable Anti-Icing Superhydrophobic Surfaces

The growing interest in flexible superhydrophobic surfaces extends beyond various practical applications like solar panels, flexible electronics, etc. This study introduces a cost-effective and environmentally friendly method to create a durable, flexible, and optically semi-transparent superhydrophobic film with an extreme anti-icing character. The prestrained polydimethylsiloxane film subjected to biofuel-based flame treatment under controlled conditions induces microwrinkles with a superimposed cluster of nanoparticles while maintaining surface flexibility and transparency. This meticulous process enhances surface roughness, achieving superhydrophobic characteristics (θ > 165˚) with a remarkably low tilting angle (<3˚) with adhesion against water <2 µN (lower than Lotus leaf). The films applied over solar panels result in <1% voltage drop within 5 s due to effective cleaning under simulated rain. The remarkable anti-icing performance of the developed film is characterized by ice adhesion <25 kPa over 50 icing/de-icing cycles attributed to the presence of nanoclusters. The films displayed exceptional resilience and sustained efficacy under prolonged exposure to harsh external environments. These superhydrophobic films, characterized by flexibility, durability, and transparency, present promising opportunities for fabricating structures, even with intricate geometries. These findings imply a significant stride in the practical utilization of superhydrophobic surfaces, demonstrating their potential in diverse real-world applications.

Plasma-based post-processing of colloidal nanocrystals for applications in heterogeneous catalysis

This review summarizes the work on the use of plasmas to post-process nanostructures, in particular colloidal nanocrystals, as promising candidates for applications of heterogeneous catalysis. Using plasma to clean or modify the surface of nanostructures is a more precisely controlled method compared to other conventional methods, which is preferable when strict requirements for nanostructure morphology or chemical composition are necessary. The ability of plasma post-processing to create mesoporous materials with high surface areas and controlled microstructure, surfaces, and interfaces has transformational potential in catalysis and other applications that leverage surface/interface processes.

Preparation of Waterborne Silicone-Modified Polyurethane Nanofibers and the Effect of Crosslinking Agents on Physical Properties

Silicone-modified polyurethane (PUSX) refers to the introduction of a silicone short chain into the polyurethane chain to make it have the dual properties of silicone and polyurethane (PU). It can be used in many fields, such as coatings, films, molding products, adhesives, and so on. The use of organic solvents to achieve the fiberization of silicone-modified polyurethane has been reported. However, it is challenging to achieve the fiberization of silicone-modified polyurethane based on an environmentally friendly water solvent. Herein, we report a simple and powerful strategy to fabricate environmentally friendly waterborne silicone-modified polyurethane nanofiber membranes through the addition of polyethylene glycol (PEG) with different molecular weights using electrospinning technology and in situ doping with three crosslinking agents with different functional groups (a polyoxazoline crosslinking agent, a polycarbodiimide crosslinking agent, and a polyisocyanate crosslinking agent) combined with various heating treatment conditions. The influence of PEG molecular weight on fiber formation was explored. The morphology, structure, water resistance, and mechanical properties were analyzed regarding the effect of the introduction of silicone into PU. The effects of the type and content of crosslinking agent on the morphology and physical properties of PUSX nanofiber membranes are discussed. These results show that the introduction of silicone can improve the water resistance and high temperature resistance of waterborne PU, and the addition of a crosslinking agent can further improve the water resistance of the sample, so that the sample can maintain good morphology after immersion. Crosslinking agents with different functional groups had different effects on the mechanical properties of PUSX nanofiber membranes due to different reactions. Among them, the oxazoline crosslinking agent had a significant effect on improving tensile strength, while the isocyanate crosslinking agent had a significant effect on improving the elongation at break. The PUSX nanofiber membrane prepared in this work did not use organic solvents that were harmful to humans and the environment, and it can be used in outdoor textiles, oil-water separation, medical health, and other fields.

Anti-Environmental Aging Passive Daytime Radiative Cooling

Passive daytime radiative cooling technology presents a sustainable solution for combating global warming and accompanying extreme weather, with great potential for diverse applications. The key characteristics of this cooling technology are the ability to reflect most sunlight and radiate heat through the atmospheric transparency window. However, the required high solar reflectance is easily affected by environmental aging, rendering the cooling ineffective. In recent years, significant advancements have been made in understanding the failure mechanisms, design strategies, and manufacturing technologies of daytime radiative cooling. Herein, a critical review on anti-environmental aging passive daytime radiative cooling with the goal of advancing their commercial applications is presented. It is first introduced the optical mechanisms and optimization principles of radiative cooling, which serve as a basis for further endowing environmental durability. Then the environmental aging conditions of passive daytime radiative cooling, mainly focusing on UV exposure, thermal aging, surface contamination and chemical corrosion are discussed. Furthermore, the developments of anti-environmental aging passive daytime radiative cooling materials, including design strategies, fabrication techniques, structures, and performances, are reviewed and classified for the first time. Last but not the least, the remaining open challenges and the insights are presented for the further promotion of the commercialization progress.

Biomimetic Wearable Sensors: Emerging Combination of Intelligence and Electronics

Owing to the advancement of interdisciplinary concepts, for example, wearable electronics, bioelectronics, and intelligent sensing, during the microelectronics industrial revolution, nowadays, extensively mature wearable sensing devices have become new favorites in the noninvasive human healthcare industry. The combination of wearable sensing devices with bionics is driving frontier developments in various fields, such as personalized medical monitoring and flexible electronics, due to the superior biocompatibilities and diverse sensing mechanisms. It is noticed that the integration of desired functions into wearable device materials can be realized by grafting biomimetic intelligence. Therefore, herein, the mechanism by which biomimetic materials satisfy and further enhance system functionality is reviewed. Next, wearable artificial sensory systems that integrate biomimetic sensing into portable sensing devices are introduced, which have received significant attention from the industry owing to their novel sensing approaches and portabilities. To address the limitations encountered by important signal and data units in biomimetic wearable sensing systems, two paths forward are identified and current challenges and opportunities are presented in this field. In summary, this review provides a further comprehensive understanding of the development of biomimetic wearable sensing devices from both breadth and depth perspectives, offering valuable guidance for future research and application expansion of these devices.

Study on the Mechanism of Rapid Oil-Water Separation by a Fe3 O4 @PMMA@PDMS Intelligent Superhydrophobic Micro/Nanorobot

We prepared an environmentally friendly intelligent Fe3 O4 @PMMA@PDMS superhydrophobic oil-absorbing material with simple process and excellent performance, and investigated the effects of different particle sizes of Fe3 O4 , different concentrations of PDMS, and different heating times on the superhydrophobicity of the coating. The best performance of the coating was achieved at a particle size combination of 20/500 nm for Fe3 O4 , a PDMS to Fe3 O4 @PMMA mass ratio of 6 : 1, and a heating time of 2 min at 400 °C. H2-SPSS coating not only has excellent superhydrophobicity, abrasion resistance, self-cleaning property, and chemical corrosion, but also has good flux and efficiency for separating oil-water mixture, with fluxes of 40,540, 32,432, and 37,027 Lm-2 h-1 for trichloromethane, dichloromethane and bromoethane, respectively, and separation efficiencies of 99.78 %, 99.74 % and 99.73 %, respectively. In addition, we also prepared a superhydrophobic magnetic polyurethane (SPPU) sponge using Fe3 O4 @PMMA@PDMS, which not only has a good oil absorption capacity of 18-44 g/g for different oil substances, it can also move directionally by magnet attraction and absorb oil along a fixed path. Under the control of the magnet, SPPU completes the whole oil absorption process in only 4 s, showing excellent oil absorption and intelligence.

Damage Tolerance of Superhydrophobic Coatings with Binary Cooperative Cells for Water Harvesting

Multifunction superhydrophobic coatings that facilitate water harvesting are attractive for addressing the daunting water crisis, yet, they are caught in a double bind when their durability is considered, as durable coatings will require both tough micro-textures to survive concentrated stress and high-surface-energy chemistry to form chemical bonds within the matrix. To date, a universal bulk-phase coating that combines multifunctionality, ultra-durability, and fabrication feasibility remains challenging. Here, a binary cooperative cell design is reported that can solve the contradiction between the multifunctionality and durability requirements of superhydrophobic coatings. In this strategy, mechanochemically tailored cells with releasable nanoseeds are infused in the common matrix, which serves both as a versatile chemical bridge to achieve strong bonds within the coating building blocks, and as an instantaneous self-repairing generator to improve durability. Such a strategy significantly boosted the wear resistance and outdoor stability of the coatings by over 30-100 and 18 folds, respectively, compared with conventional coatings. The coating is applied to the sustainable application, i.e., enhancing the water collection efficiency by at least 1000% even after harsh abrasion. The strategy will broaden the vision in handling the dilemma properties among functional coatings and promote the application of superhydrophobic coatings in extreme environments.

A UV-Resistant Heterogeneous Wettability-Patterned Surface

Preparing UV-resistant heterogeneous wettability patterns is critical for the practical application of surfaces with heterogeneous wettability. However, combining UV-resistant superhydrophobic and superhydrophilic materials on heterogeneous surfaces is challenging. Inspired by the structure of cell membranes, a UV-resistant heterogeneous wettability-patterned surface (UPS) is designed via laser ablation of the coating of multilayer structures. UV-resistant superhydrophobic silica patterns can be created in situ on surfaces covered with superhydrophilic TiO2 nanoparticles. The UV resistance time of the UPS with a TiO2 -based surface is more than two orders of magnitude higher than that obtained with other surface molecular modification methods that require a mask. The cell-membrane-like structure of the UPS regulates the migration of internal siloxane chain segments in the hydrophilic and hydrophobic regions of the surface. The UPS enables efficient patterning of functional materials under UV irradiation, controlling the wetting behavior of liquids in open-air systems. Furthermore, its heterogeneous wettability remains stable even after 50 h of intense UV irradiation (365 nm, 500 mW cm-2 ). These UV-resistant heterogeneous wettability patterned surfaces will likely be applied in microfluidics, cell culture, energy conversion, and water collection in the future.

Ultra-durable superhydrophobic cellular coatings

Developing versatile, scalable, and durable coatings that resist the accretion of matters (liquid, vapor, and solid phases) in various operating environments is important to industrial applications, yet has proven challenging. Here, we report a cellular coating that imparts liquid-repellence, vapor-imperviousness, and solid-shedding capabilities without the need for complicated structures and fabrication processes. The key lies in designing basic cells consisting of rigid microshells and releasable nanoseeds, which together serve as a rigid shield and a bridge that chemically bonds with matrix and substrate. The durability and strong resistance to accretion of different matters of our cellular coating are evidenced by strong anti-abrasion, enhanced anti-corrosion against saltwater over 1000 h, and maintaining dry in complicated phase change conditions. The cells can be impregnated into diverse matrixes for facile mass production through scalable spraying. Our strategy provides a generic design blueprint for engineering ultra-durable coatings for a wide range of applications.

Scalable and Mechanically Durable Superhydrophobic Coating of SiO2/Polydimethylsiloxane/Epoxy Nanocomposite

The mechanical durability of superhydrophobic surfaces is of significance for their practical applications. However, few reports about superhydrophobic coating on certain substrates took into consideration both the mechanical stability of the superhydrophobic coating and adhesion stability between the coating and the substrate. Herein, we put forward a facile and efficient strategy to construct robust superhydrophobic coatings by simply spray-coating a composite suspension of SiO₂ nanoparticles, polydimethylsiloxane (PDMS), and epoxy resin (EP) on substrates pretreated with an EP base-coating. The as-obtained coating exhibited excellent superhydrophobicity with water contact angle of 163° and sliding angle of 3.5°, which could endure UV irradiation of 180 h, immersion in acidic or basic solutions for 168 h, and outdoor exposure for over 30 days. Notably, the coating surface retained superhydrophobicity after being successively impacted with faucet water for 1 h, impinged with 360 g sand grains, and abraded with sandpaper of 120 grid under a load of 500 g for 5 m distance. The outstanding mechanical stability was mainly attributed to the cross-linking of EP and the elastic nature of PDMS which ensured strong cohesion inside the whole coating and to the substrate. Additionally, the coating showed self-healing capacity against O₂ plasma etching. The method is simple with the materials commercially available and is expected to be widely applied in outdoor applications.

Advances in Bioinspired Superhydrophobic Surfaces Made from Silicones: Fabrication and Application

As research on superhydrophobic materials inspired by the self-cleaning and water-repellent properties of plants and animals in nature continues, the superhydrophobic preparation methods and the applications of superhydrophobic surfaces are widely reported. Silicones are preferred for the preparation of superhydrophobic materials because of their inherent hydrophobicity and strong processing ability. In the preparation of superhydrophobic materials, silicones can both form micro-/nano-structures with dehydration condensation and reduce the surface energy of the material surface because of their intrinsic hydrophobicity. The superhydrophobic layers of silicone substrates are characterized by simple and fast reactions, high-temperature resistance, UV resistance, and anti-aging. Although silicone superhydrophobic materials have the disadvantages of relatively low mechanical stability, this can be improved by the rational design of the material structure. Herein, we summarize the superhydrophobic surfaces made from silicone substrates, including the cross-linking processes of silicones through dehydration condensation and hydrosilation, and the surface hydrophobic modification by grafting hydrophobic silicones. The applications of silicone-based superhydrophobic surfaces have been introduced such as self-cleaning, corrosion resistance, oil-water separation, etc. This review article should provide an overview to the bioinspired superhydrophobic surfaces of silicone-based materials, and serve as inspiration for the development of polymer interfaces and colloid science.

Electrospun Nanofibrous Membranes: A Versatile Medium for Waterproof and Breathable Application

Waterproof and breathable membranes that prevent liquid water penetration, while allowing air and moisture transmission, have attracted significant attention for various applications. Electrospun nanofiber materials with adjustable pore structures, easily tunable wettability, and good pore connectivity, have shown significant potential for constructing waterproof and breathable membranes. Herein, a systematic overview of the recent progress in the design, fabrication, and application of waterproof and breathable nanofibrous membranes is provided. The various strategies for fabricating the membranes mainly including one-step electrospinning and post-treatment of nanofibers are given as a starting point for the discussion. The different design concepts and structural characteristics of each type of waterproof and breathable membrane are comprehensively analyzed. Then, some representative applications of the membranes are highlighted, involving personal protection, desalination, medical dressing, and electronics. Finally, the challenges and future perspectives associated with waterproof and breathable nanofibrous membranes are presented.

Microskeleton Magnetic Nanofiller Composite with Highly Reliable Superhydrophobic Protection for Long-Lived Electromagnetic Interface Shielding

Superhydrophobic/electromagnetic interference (EMI) shielding materials have received a great deal of attention, attributing to their excellent water repellence characteristic. However, it is really challenging to simultaneously achieve materials with superhydrophobicity, high EMI shielding performance, and long-term stability of these materials that can operate around the clock in harsh service conditions. Herein, a novel strategy to create an integrated microskeleton magnetic nanofiller composite (IMMNC) with exceptional liquid repellency, enhanced EMI shielding effectiveness, and extreme environment reliability is reported. The superhydrophobicity of the IMMNC was maintained after extreme mechanical and chemical damage due to the synergistic enhancement between epoxy-silicone oligomers/polymerized rosin and microskeleton. Consecutively hierarchical micro/nanoarchitectures and conductive pathways endow the IMMNC with a high EMI shielding effectiveness up to 80.7 dB and a satisfactory antifouling capacity for solid and water-based contaminants. More interestingly, this composite still maintains a superior EMI shielding performance after being subjected to ultrasonic vibration, low (-20 °C) or high temperature (300 °C), and even strong acid (1 M), demonstrating its great potential and reliability as a high-performance EMI shielding material resistant to harsh operating conditions. This work provides an efficient and practical solution for developing next-generation EMI shielding materials with high reliability in an all-weather complex and changeable environment.

Fabrication of robust superhydrophobic magnetic multifunctional coatings and liquid marbles

To obtain durable and multi-function superhydrophobic surfaces, we reported a facial method to prepare a multifunctional suspension (γ-Fe₂O₃@SiO₂@PDMS suspension) named as FSP suspension, in which γ-Fe₂O₃ was coated by the silica shell and PDMS was used as the outer layer. Superhydrophobic magnetic polyurethane (SMPU) sponge was prepared by immersing the polyurethane (PU) sponge into the FSP suspension, exhibiting the superior ability to absorb oil. In addition, it could also move directionally by the attraction of magnets and absorb the oil along the fixed path. The heated superhydrophobic magnetic stainless steel (H-SMSS) mesh was acquired by spraying FSP suspension onto the stainless steel mesh and then heating at 400 °C, which demonstrated superior superhydrophobicity and resistance to abrasion and chemical corrosion. Besides, the H-SMSS mesh displayed excellent flux and efficiency to separate the oil/water mixture. Rolling droplets on FSP particles, the superhydrophobic magnetic liquid marbles (SMLMs) were fabricated, in which liquids with different volumes were encapsulated and transported directionally. Further, it was convenient to inject liquid into the SMLM and withdraw liquid from it. Thus, the prepared FSP suspension has promising applications in constructing large-area, robust, and multifunctional surfaces and microreactors.

Effect of functional group and structure on hydrophobic properties of environment-friendly lignin-based composite coatings

Hydrophobic coatings are widely used in a variety of materials surfaces. However, it remains a great challenge for the non-toxic and environmentally-friendly production of hydrophobic coatings. Herein, two nano-scale spherical lignin/SiO₂ composite particles are synthesized based on the electrostatic interaction and the steric hindrance effect inspired by the self-protection of straw. Introduction of positively charged quaternary ammonium enhances the possibility of electrostatic self-assembly between lignin and SiO₂ for QAL/SiO₂, and access of super-long hydrophobic chains induces the formation of nano-sized particles for QALC₁₂/SiO₂. The coatings were fabricated by simply spraying on substrates and hydrophilic/hydrophobic properties were detected. The results show that the long hydrophobic chain can enhance the hydrophobic properties of lignin polymers (CA = 129°) and the spherical micro-nano structure is beneficial to improve the hydrophobic properties of the lignin/SiO₂ composite (CA = 137°). Meanwhile, the hydrophobic coating has good self-cleaning performance. The excellent hydrophobic and self-cleaning properties are mainly benefited from the nano effect, reasonable hydrophilic/hydrophobic structure, and good dispersibility of spherical structure. This work not only provides a kind of lignin-based nano-scale waterproof coatings holding excellent properties in terms of cost, scalability, and robustness, but also has important significance for the high-value utilization of biomass resources.

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.

A fabric-based superhydrophobic ACNTs/Cu/PDMS heater with an excellent electrothermal effect and deicing performance

The fabric not only has good electrical conductivity, chemical stability and mechanical durability, but also exhibits excellent electrothermal effects and de-icing properties. In addition, it can be used to monitor various movements of the human body.

Underwater Drag Reduction and Buoyancy Enhancement on Biomimetic Antiabrasive Superhydrophobic Coatings

A superhydrophobic (SHB) surface with an excellent self-cleaning ability is of great significance in both human survival and industrial fields. However, it is still a challenge to achieve large-area preparation of antiabrasive SHB surfaces with great mechanical robustness for broader applications. Thus, a kind of facile SHB coating with excellent liquid repellency and antiresistance is constructed by spraying a fluorine-free suspension consisting of epoxy resin, hexadecyltrimethoxysilane (HDTMS), and silica nanoparticles on a glass sheet. The SHB coating not only shows high adhesion on various materials but also has high water repellency under various test conditions, including tape peeling after blade scraping, sandpaper abrasion, and immersing in a complex environment. Additionally, the SHB spheres coated with laser-induced microstructure armor could form a continuous gas cavity during the water entry process, which is essential to prolonging the drag reduction ability of SHB coatings in liquid. Finally, the prepared robust SHB coatings have been employed in underwater buoyancy enhancement and reducing fluid resistance, which may open new avenues for underwater drag reduction in the field of marine applications.

Robust, Multiresponsive, Superhydrophobic, and Oleophobic Nanocomposites via a Highly Efficient Multifluorination Strategy

Artificial superhydrophobic surfaces are garnering constant attention due to their wide applications. However, it is a great challenge for superhydrophobic materials to simultaneously achieve good oil repellency, mechanochemical robustness, adhesion, thermomechanical properties, and multiresponsive ability. Herein, we propose a highly efficient multifluorination strategy to prepare superhydrophobic nanocomposites with the above features, which can be used as monoliths or coatings on various substrates. In this strategy, long-chain perfluorinated epoxy (PFEP) provides outstanding water/oil repellency, tetrafluorophenyl-based epoxy (FEP) possesses good thermodynamic compatibility with PFEP and increases the mechanical performance of the matrix, and carbon nanotubes grafted with perfluorinated segments and flexible spacers (FCNTs) tailor the surface roughness as well as impart multiple functions and ensure good binding interfaces. Notedly, all of the applications of constrained long-chain perfluorinated compounds are achieved via thiol-ene click chemistry, following the ethos of atom economy. The resultant PFEP₃₀/FCNTs₄₀ exhibits superhydrophobicity and oleophobicity, thermal conductivity (1.33 W·m^-1·K^-1), electronic conductivity (232 S m^-1), and electromagnetic interference shielding properties (∼30 dB at 8.2-12.4 GHz, 200 μm). Importantly, after different extreme physical/chemical tests, the PFEP₃₀/FCNTs₄₀ coating still shows outstanding water/oil repellency. In addition, the coating exhibits good photo/electrothermal conversion ability and shows the potential for sensor application. Moreover, the novel strategy provides an efficient guideline for large-scale preparation of robust, multiresponsive, superhydrophobic, and oleophobic materials.

The challenges, achievements and applications of submersible superhydrophobic materials

Superhydrophobic materials have been widely reported throughout the scientific literature. Their properties originate from a highly rough morphology and inherently water repellent surface chemistry. Despite promising an array of functionalities, these materials have seen limited commercial development. This could be attributed to many factors, like material compatibility, low physical resilience, scaling-up complications, etc. In applications where persistent water contact is required, another limitation arises as a major concern, which is the stability of the air layer trapped at the surface when submerged or impacted by water. This review is aimed at examining the diverse array of research focused on monitoring/improving air layer stability, and highlighting the most successful approaches. The reported complexity of monitoring and enhancing air layer stability, in conjunction with the variety of approaches adopted, results in an assortment of suggested routes to achieving success. The review is addressing the challenge of finding a balance between maximising water repulsion and incorporating structures that protect air pockets from removal, along with challenges related to the variant approaches to testing air-layer stability across the research field, and the gap between the achieved progress and the required performance in real-life applications.

Ultrafast Flame-Induced Pyrolysis of Poly(dimethylsiloxane) Foam Materials toward Exceptional Superhydrophobic Surfaces and Reliable Mechanical Robustness

Superhydrophobic surfaces are imperative in flexible polymer foams for diverse applications; however, traditional surface coatings on soft skeletons are often fragile and can hardly endure severe deformation, making them unstable and highly susceptible to cyclic loadings. Therefore, it remains a great challenge to balance their mutual exclusiveness of mechanical robustness and surface water repellency on flexible substrates. Herein, we describe how robust superhydrophobic surfaces on soft poly(dimethylsiloxane) (PDMS) foams can be achieved using an extremely simple, ultrafast, and environmentally friendly flame scanning strategy. The ultrafast flame treatment (1-3 s) of PDMS foams produces microwavy and nanosilica rough structures bonded on the soft skeletons, forming robust superhydrophobic surfaces (i.e., water contact angles (WCAs) > 155° and water sliding angles (WSAs) < 5°). The rough surface can be effectively tailored by simply altering the flame scanning speed (2.5-15.0 cm/s) to adjust the thermal pyrolysis of the PDMS molecules. The optimized surfaces display reliable mechanical robustness and excellent water repellency even after 100 cycles of compression of 60% strain, stretching of 100% strain, and bending of 90° and hostile environmental conditions (including acid/salt/alkali conditions, high/low temperatures, UV aging, and harsh cyclic abrasion). Moreover, such flame-induced superhydrophobic surfaces are easily peeled off from ice and can be healable even after severe abrasion cycles. Clearly, the flame scanning strategy provides a facile and versatile approach for fabricating mechanically robust and surface superhydrophobic PDMS foam materials for applications in complex conditions.

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.

Robust Superamphiphilic Membrane with a Closed-Loop Life Cycle

Oil-spill remediation is an international environmental challenge, and superamphiphilic membranes, as a promising solution, have recently drawn lots of attention. However, the robustness of the conventional membrane design is less satisfying under severe conditions during practical applications. Additionally, it is unavoidable for the membranes to face a series of foulants in their practical working environment, for example, algae and sand. These foulants will block the membrane, which leads to a new economic and environmental problem in terms of waste management at the end of their life. To address the aforementioned challenges, a new generation of superamphiphilic vitrimer epoxy resin membranes (SAVER) to separate oil and water efficiently is reported. Similar to classical epoxy resins, SAVER shows strong mechanical robustness and sustains exposure to aqua regia and sodium hydroxide solutions. Furthermore, the blocked membrane can be easily recovered when contaminated with mixed foulants by using dynamic transesterification reactions in the polymer network. The ease with which biobased SAVER can be manufactured, used, recycled, and re-used without losing value points to new directions in designing a closed-loop superamphiphilic membrane life cycle.

Robust superhydrophobicity: mechanisms and strategies

Superhydrophobic surfaces hold great prospects for extremely diverse applications owing to their water repellence property. The essential feature of superhydrophobicity is micro-/nano-scopic roughness to reserve a large portion of air under a liquid drop. However, the vulnerability of the delicate surface textures significantly impedes the practical applications of superhydrophobic surfaces. Robust superhydrophobicity is a must to meet the rigorous industrial requirements and standards for commercial products. In recent years, major advancements have been made in elucidating the mechanisms of wetting transitions, design strategies and fabrication techniques of superhydrophobicity. This review will first introduce the mechanisms of wetting transitions, including the thermodynamic stability of the Cassie state and its breakdown conditions. Then we highlight the development, current status and future prospects of robust superhydrophobicity, including characterization, design strategies and fabrication techniques. In particular, design strategies, which are classified into passive resistance and active regeneration for the first time, are proposed and discussed extensively.

Microparticle Suspensions and Bacteria-Laden Droplets: Are They the Same in Terms of Wetting Signature?

Adhesion behavior of microbial pathogens on commonly encountered surfaces is one of the most pertinent questions now. We present the characterization of bacteria-laden droplets and quantify the adhesion forces on highly repellent surfaces with the help of a simple experimental setup. Comparing the force signature measured directly using an in-house capillary deflection-based droplet force apparatus, we report an anomalous adhesion behavior of live bacteria (E. coli)-laden droplets on repellent surfaces, which stands in stark contrast to the observed adhesion signature when the doping agent is changed to inert microparticles or the same bacteria in an incapacitated state. We showed that the regular contact angle measurements using optical goniometry is unable to differentiate between the live bacteria and the dead ones (including microparticles) and thus delineate its limitations and the complementary nature of the adhesion measurements in understanding the fundamental interfacial interaction of living organisms on solid surfaces.

Dipping-Press Coating Method for Retaining Transparency and Imparting Hydrophobicity Regardless of Plastic Substrate Type

Plastics are used in cover substrates for billboards, windows, large LED signboards, lighting devices, and solar panels because they are transparent and can be colored and shaped as desired. However, when plastic cover substrates installed in outdoor environments are constantly exposed to harsh conditions such as snow, rain, dust, and wind, their transparency deteriorates owing to watermarks and dust contamination. Herein, we investigated a simple dipping-press coating method that can impart hydrophobicity while maintaining the transparency, regardless of the plastic substrate type. A highly transparent and hydrophobic coating film was formed on a plastic substrate by a two-step process, as follows: (1) application of a polydimethylsiloxane–octadecylamine coating by a dipping process, and (2) embedding (1H,1H,2H,2H-heptadecafluorodec-1-yl) phosphonic acid–aluminum oxide nanoparticles by a thermal press process. The plastic substrates on which the highly transparent and hydrophobic coating film was formed showed 150° or higher hydrophobicity and 80% or higher visible light transparency. The coating method proposed herein can easily impart hydrophobicity and is compatible with any plastic substrate that must maintain prolonged transparency without contamination when exposed to adverse conditions.

Durable fire retardant, superhydrophobic, abrasive resistant and air/UV stable coatings

Fabric-based materials such as textiles and papers are widely used in our daily life. However, most of conventional fabrics are highly combustible and easily stained by water and household liquids, susceptible to fire risks and surface contamination/staining. Herein, a non-fluorinated coating that contains the flame-retardants ammonium polyphosphate/pentaerythrotol (APP/PER) and water-repellent silica nanoparticles-polydimethylsiloxane (SiO₂@PDMS) is developed. The coated fabric materials prevent fire propagation and are repellant to water, coffee, milk etc. The heat release rate of the SiO₂@PDMS/APP/PER-coated cotton fabric is 46.33% lower than that of pure cotton fabric, and the amount of the char yield is increased by 40.4%. The coatings are durable, resistant to mechanical abrasion and have a long life-time exposure to corrosive liquids and intense UV radiation. The coated fabric materials also exhibit good organic solvent/oil and water separation capability at reduced risks of fire. The facile process can be extended to garment and paper industries to lower the fire risks and resist water stains.

Suppressing Evaporative Loss in Slippery Liquid-Infused Porous Surfaces (SLIPS) with Self-Suspended Perfluorinated Nanoparticles

This article describes an approach to resolving the issue of evaporative loss from slippery liquid-infused porous surfaces (SLIPS). Hydrophobic and oleophobic fluids with significantly reduced evaporative loss rates at temperatures of up to 90 °C were obtained by the one-step mixing of commercially available perfluorinated lubricants with colloidal nanoparticles to form self-suspended nanoparticle fluids (i.e., suspensions nearly devoid of solvent). No evaporative loss was detected at temperatures of as high as 50 °C for over 3 months. Furthermore, the approach allows us to combine the function of the nanoparticles with the slippery characteristic of SLIPS.

Nitric Oxide Release Device for Remote-Controlled Cancer Therapy by Wireless Charging

Traditional phototherapies face the issue that the insufficient penetration of light means it is difficult to reach deep lesions, which greatly reduces the feasibility of cancer therapy. Here, an implantable nitric oxide (NO)-release device is developed to achieve long-term, long-distance, remote-controllable gas therapy for cancer. The device consists of a wirelessly powered light-emitting diode (wLED) and S-nitrosoglutathione encapsulated with poly(dimethylsiloxane) (PDMS), obtaining the NO-release wLED (NO-wLED). It is found that NO release from the NO-wLED can be triggered by wireless charging and the concentration of produced NO reaches 0.43 × 10^-6 m min^-1 , which can achieve a killing effect on cancer cells. In vivo anticancer experiments exhibit obvious inhibitory effect on the growth of orthotopic cancer when the implanted NO-wLED is irradiated by wireless charging. In addition, recurrence of cancer can be prevented by NO produced from the NO-wLED after surgery. By illumination in the body, this strategy overcomes the poor penetration and long-wavelength dependence of traditional phototherapies, which also provides a promising approach for in vivo gas therapy remote-controlled by wireless charging.

Facile fabrication of fluorine-free breathable poly(methylhydrosiloxane)/polyurethane fibrous membranes with enhanced water-resistant capability

HYPOTHESIS

Ideal breathable and waterproof materials contain two key elements: hydrophobic matrix and small pore size. Current high-performing breathable waterproof membranes usually employ fluorinated materials to construct hydrophobic surface, which possess alarming potential environmental hazards. Fluorine-free waterproof agents through coating treatment to obtain hydrophobicity suffer from complicated fabrication process and poor durability. Hence, non-fluorinated chemicals incorporated into fibers via a facile one-step electrospinning may be an effective approach to attain durable hydrophobic membranes.

EXPERIMENTS

Poly(methylhydrosiloxane)/polyurethane (PMHS/PU) solution with various PMHS concentration was formulated and electrospun to fibrous membranes, followed by a facile thermal treatment process. A systematic study including morphologies, porous structure, and surface wettability was performed. Breathable waterproof performance and tensile strength were also investigated.

FINDINGS

Added PMHS imparted mighty hydrophobicity to the membranes with a water contact angle of 130.2°, and the subsequent heat treatment greatly improved waterproofness, meanwhile doubled the tensile strength. The resultant membranes exhibited robust hydrostatic pressure of 54.1 kPa, medium breathability of 9.5 kg m^-2 d^-1, and excellent stretching stress of 14.1 MPa, which can meet the requirements of general use. The presented strategy on membrane fabrication is feasible and scalable, which may be considered as an effective remedy for environmental protection.

Superhydrophobic Foams with Chemical- and Mechanical-Damage-Healing Abilities Enabled by Self-Healing Polymers

The fabrication of superhydrophobic materials capable of spontaneously healing both chemical and mechanical damages at ambient conditions has been a great challenge but highly desired. In this study, we propose that a self-healing hydrophobic polymer can be used to induce self-healing in a superhydrophobic material. As a demonstration, stable and porous self-healing superhydrophobic foams are fabricated by casting a mixture of healable poly(dimethylsiloxane) (PDMS)-based polyurea, multiwalled carbon nanotubes (MCNTs), and table salt, followed by solvent evaporation and removal of the salt template. The PDMS-based polyurea is able to heal mechanical damage by reforming hydrogen bonds and can also reverse chemical damage through surface reorganization. Thus, the chemically and mechanically damaged foams can spontaneously restore their superhydrophobicity and structural integrity at ambient conditions. Moreover, because of the satisfactory photothermal conversion of MCNTs, the temperature of the self-healing superhydrophobic foams can rapidly reach 60 °C under sunlight, which greatly increases the healing speed and healing efficiency of the foam.

Self-Limiting Processes in the Flame-Based Fabrication of Superhydrophobic Surfaces from Silicones

Outdoor applications of superhydrophobic coatings require synthetic approaches that allow their simple, fast, scalable, and environmentally benign deployment on large, heterogeneous surfaces and their rapid regeneration in situ. We recently showed that the thermal degradation of silicones by flames fulfills these characteristics by spontaneously structuring silicone surfaces into a hierarchical, textured structure that provides wear-resistant, healable superhydrophobicity. This paper elucidates how flame processing-a simple, rapid, and out-of-equilibrium process-can be so counterintuitively reliable and robust in producing such a complex structure. A comprehensive study of the effect of the processing speed and flame temperature on the chemical and physical properties of the coatings yielded three surprising results. (i) Three thermal degradation mechanisms drive the surface texturing: depolymerization (in the O₂-rich conditions of the surface), decomposition (in the O₂-poor conditions found a few micrometers from the surface), and pyrolysis at excessive temperatures. (ii) The operational condition is delimited by the onset of the depolymerization at low temperatures and the onset of pyrolysis at high temperatures. (iii) The remarkably wide operational conditions and robustness of this approach result from self-limiting growth and oxidation of the silicone particles that are responsible for the surface texturing and in the extent of their deposition. As a result of this analysis we show that superhydrophobic surfaces can be produced or regenerated with this approach at a speed of 15 cm s^-1 (i.e., the length of an airport runway in ∼4.5 h).

Bioinspired Soot-Deposited Janus Fabrics for Sustainable Solar Steam Generation with Salt-Rejection

Inspired by lotus leaves, self-floating Janus cotton fabric is successfully fabricated for solar steam generation with salt-rejecting property. The layer-selective soot-deposited fabrics not only act as a solar absorber but also provide the required superhydrophobicity for floating on the water. With a polyester protector, the prepared Janus evaporator exhibits a sustainable evaporation rate of 1.375 kW m-2 h-1 and an efficiency of 86.3% under 1 sun (1 kW m-2) and also performs well under low intensity and inclined radiation. Furthermore, no special apparatus and/or tedious processes are needed for preparing this device. With a cost of less than $1 per m2, this flexible Janus absorber is a promising tool for portable solar vapor generator.

PDMS-Infused Poly(High Internal Phase Emulsion) Templates for the Construction of Slippery Liquid-Infused Porous Surfaces with Self-cleaning and Self-repairing Properties

Advanced liquid-repelling materials that resist both water-based and oil-based contaminants have significant applications in many fields. Herein, a novel protocol for the fabrication of a robust poly(high internal phase emulsion) (polyHIPE)-based slippery liquid-infused porous surface (SLIPS) system with combined self-repairing and self-cleaning properties is developed. Specifically, polystyrene-based polyHIPE (PS-HIPE) membranes with an interconnected porous structure were prepared from polymerization of the continuous oil phase in the water-in-oil HIPE templates. These polyHIPE membranes were used, for the first time, as porous substrates for loading low surface tension silicone oils as lubricating liquids for the fabrication of polyHIPE-based SLIPS membranes. These polyHIPE-based SLIPS membranes could easily repel both water- and oil-based contaminants (e.g., ink, milk, and coffee) with very low sliding angles (3.0 ? 1.3?) and could even repel solid contaminants (e.g., dust) upon washing with water. Meanwhile, such membranes exhibit excellent self-repairing properties so that physical scratching damage, such as cutting a trench, does not affect the liquid-repelling performance. The liquid-repelling ability could be recovered completely within 10 s. More significantly, such a SLIPS membrane shows excellent durability so that the water sliding angle of the SLIPS could be maintained at less than 5.0? for about 80 cycles owing to the regenerated poly(dimethylsiloxane) layer on the surface. This work represents a robust methodology to enrich the development of hydrophobic and oleophobic slippery surfaces, which is promising for many areas, such as biomedical, self-cleaning, antifouling, and self-repairing materials.

Fabrication of superhydrophobic coatings with self-cleaning properties on cotton fabric based on Octa vinyl polyhedral oligomeric silsesquioxane/polydimethylsiloxane (OV-POSS/PDMS) nanocomposite

HYPOTHESIS

Wetting behavior of solid surfaces plays an important role in various industrials and even daily life applications. Controlling the surface wettability through fabricating strongly hydrophilic or hydrophobic properties is achieved by tailoring surface topography and chemical composition. Polyhedral oligomeric silsesquioxanes (POSSs) are a class of hybrid materials with the possibility of hydrophobicity enhancement through simultaneous increase in surface roughness and reduction of surface energy.

EXPERIMENTS

In this study, octavinyl-POSS (OV-POSS) structures were utilized in fabrication of superhydrophobic cotton fabric. Coating was successfully performed through creating a two-layer topography via spraying method. In brief, surface roughness was enhanced by spraying a base layer of TiO₂ sol over the surface followed by applying a nanocomposite layer composed of 0.02 wt% of POSS in polydimethylsiloxane (PDMS).

FINDINGS

It was observed that, water contact angle (WCA) of pristine and TiO₂ coated fabric was enhanced from 0° up to ∼168° using 0.02 wt% OV-POSS/PDMS nanocomposite with a water sliding angle (WSA) of <10°. According to the results, environmentally friendly nature of precursors, high thermal, mechanical and chemical stability, self-cleaning and anti-adhesion propertiesof the as-prepared coating and simple preparation method with no special post-treatment requirement, confirm that the as-prepared coating is perfect candidate for large-scaled applications.

A facile coating with water-repellent and flame-retardant properties on cotton fabric

We herein present a facile method to fabricate functional cotton fabric (CF) with superhydrophobic surface and excellent fire-resistance property by coating with chitosan (CS)/phytic acid (PA) layer and hydrophobic silicon dioxide nanoparticles.

Multifunctional WS2&M-AgNPs superhydrophobic conductive sponges for application in various sensors

Superhydrophobic conductive sponge is prepared by an easy method based on WS₂ nanosheets and modified Ag nanoparticles in this work, which is promising to apply in various sensors derived from superior liquid repellence, thermo stability, conductive property, mechanical and chemical durability.