Reinforced Superhydrophobic Coating on Silicone Rubber for Longstanding Anti-Icing Performance in Severe Conditions

Oriented bouncing of droplets with a small Weber number on inclined one-dimensional nanoforests

Asymmetric superhydrophobic structures with anisotropic wettability can achieve directional bouncing of droplets and thus can have applications in directional self-cleaning, liquid transportation, and heat transfer. To achieve convenient large-scale preparation of asymmetric superhydrophobic surfaces, inclined nanoforests are prepared in this work using a technique of competitive ablation polymerization, which allows the control of the inclined angles, diameters, and heights of the nanostructures. In this study, such asymmetric structures with the smallest dimension (230 nm diameter) known are achieved by a simple etching method to guide droplet unidirectional bouncing. With such nanoforests, the mechanism of droplet bouncing on their surface is investigated, and controllable droplet bouncing over a long distance is achieved using droplets with a low Weber number. The proposed structure has a promising future in directional self-cleaning, liquid transportation and heat transfer.

Functionalization of Ti64 via Direct Laser Interference Patterning and Its Influence on Wettability and Oxygen Bubble Nucleation

The nucleation of bubbles on solid surfaces is an important phenomenon in nature and technological processes like electrolysis. During proton-exchange membrane electrolysis, the nucleation and separation of the electrically nonconductive oxygen in the anodic cycle plays a crucial role to minimize the overpotential it causes in the system. This increases the efficiency of the process, making renewable energy sources and the "power-to-gas" strategy more viable. A promising approach is to optimize gas separation by surface functionalization in order to apply a more advantageous interface to industrial materials. In this work, the connection between the wettability and bubble nucleation of oxygen is investigated. For tailoring the wettability of Ti64 substrates, the direct laser interference patterning method is applied. A laser source with a wavelength of 1064 nm and a pulse duration of 12 ps is used to generate periodic pillar-like structures with different depths up to ∼5 μm. The resulting surface properties are characterized by water contact angle measurement, scanning electron microscopy, confocal microscopy, and X-ray photon spectroscopy. It was possible to generate structures with a water contact angle ranging from 20° up to nearly superhydrophobic conditions. The different wettabilities are validated based on X-ray photon spectroscopy and the different elemental composition of the samples. The results indicate that the surface character of the substrate adapts depending on the surrounding media and needs more time to reach a steady state for deeper structures. A custom setup is used to expose the functionalized surfaces to oxygen-oversaturated solutions. It is shown that a higher hydrophobicity of the structured surface yields a stronger interaction with the dissolved gas. This significantly enhances the oxygen nucleation up to nearly 350% by generating approximately 20 times more nucleation spots, but also smaller bubble sizes and a reduced detachment rate.

Preparation methods and research progress of super-hydrophobic anti-icing surface

The problem of surface icing poses a serious threat to people's economy and safety, especially in the fields of aerospace, wind power generation and circuit transmission. Super-hydrophobic has excellent anti-icing performance, so it has been widely studied. As the most promising anti-icing technology, superhydrophobic anti-icing surface should not only be simple to prepare, but also have excellent comprehensive performance, which can meet the anti-icing task under harsh working conditions and long-term durability. This paper summarizes the basic performance requirements of superhydrophobic surface for anti-icing operation, and then summarizes the preparation methods and existing problems of superhydrophobic surface in recent years. Finally, the future development trend of superhydrophobic anti-icing surface is prospected and discussed, hoping to provide certain technical guidance for the subsequent research of high-performance superhydrophobic anti-icing surface.

Recent progress in understanding the anti-icing behavior of materials

Despite the significant progress in fundamental research in the physics of atmospheric icing or the revolutionary changes in modern materials and coatings achieved due to the recent development of nanotechnology and synthetic chemistry, the problem of reliable protection against atmospheric icing remains a hot topic of surface science. In this paper, we present a brief analysis of the mechanisms of anti-icing behavior that attracted the greatest interest of the scientific community and approaches which realize these mechanisms. We also note the strengths and weaknesses of such approaches and discuss future studies and prospects for the practical application of developed coatings.

Effect of Fluorosilicone Rubber on Mechanical Properties, Dielectric Breakdown Strength and Hydrophobicity of Methyl Vinyl Silicone Rubber

Silicone rubber (SIR) is used in high-voltage insulators because of its insulation, and excellent hydrophobicity is very important in harsh outdoor environments. To enhance the hydrophobicity and low-temperature resistance of silicone rubber, methyl vinyl silicone rubber and fluorosilicone rubber (FSIR) blend composites with different ratios were prepared. The samples were characterized and analyzed using scanning electron microscopy, tensile testing, dynamic mechanical analysis and static contact angle testing. The results showed that after blending, SIR and FSIR were well compatible. FSIR had higher elastic modulus and reduced the tensile strength to some extent in SIR/FSIR composites. The addition of a small amount of FSIR made its crystallization temperature decrease from -30 to -45 °C, meaning that the low-temperature resistance was significantly improved. The breakdown strength of SIR/FSIR composites can still be maintained at a high level when a small amount of FSIR is added. The contact angle of the composites increased from 108.9 to 115.8° with the increase in FSIR content, indicating the enhanced hydrophobicity. When the samples were immersed in water for 96 h, the hydrophobicity migration phenomenon occurred. The static contact angle of the samples with less FSIR content had a weaker decreasing trend, which illustrated that the hydrophobicity was maintained at a high level.

Advances in the research of carbon-, silicon-, and polymer-based superhydrophobic nanomaterials: Synthesis and potential application

With the rapid development of science and technology, superhydrophobic nanomaterials have become one of the hot topics from various subjects. Due to their distinct properties, such as superhydrophobicity, anti-icing and corrosion resistance, superhydrophobic nanomaterials are widely used in industry, agriculture, defense, medicine and other fields. Hence, the development of superhydrophobic materials with superior performance, economical, practical features, and environment-friendly properties are extremely important for industrial development and environmental protection. Aimed to provide a scientific and theoretical basis for the subsequent study on the preparation of composite superhydrophobic nanomaterials, this paper reviewed the latest progress in the research of superhydrophobic surface wettability and the theory of superhydrophobicity, summarized and analyzed the latest development of carbon-based, silicon-based and polymer-based superhydrophobic nanomaterials in terms of their synthesis, modification, properties and structure sizes (diameters), discussed the problems and unique application prospects of carbon-based, silicon-based and polymer-based superhydrophobic nanomaterials.

An Extreme-Environment-Resistant Self-Healing Anti-Icing Coating

Anti-icing coatings on outdoor infrastructures and transportations inevitably suffer from surface injuries, especially in extreme weather events (e.g., freezing weather or acid rain). The coating surface damage can result in anti-icing performance loss or even icing promotion. The development of anti-icing coatings that enables self-healing in extreme conditions is highly desired but still challenging. Herein, an extreme-environment-resistant self-healing anti-icing coating is developed by integrating fluorinated graphene (FG) into a supramolecular polymeric matrix. The coating exhibits both anti-icing and deicing performance (ice nucleation temperature is ≈-30.3 °C; ice shear strength is ≈48.7 kPa), mainly attributable to the hydrophobic FG and silicone-based supramolecular material. Notably, owing to the crosslinking polymeric network with various dynamic bonds, this coating can sustain anti-icing/deicing performance after autonomous self-healing under harsh conditions including low temperature (-20 °C), strong acid (pH = 0), and strong alkali (pH = 14) environments. This coating paves the way to meet the anti-icing demand in open air, especially for the infrastructures in polar regions or acid/alkali environments.

Fluorine-free preparation of a superhydrophobic coating with anti-icing properties, mechanical durability and self-cleaning effect

Superhydrophobic materials have become a feasible choice to solve related difficult problems because of their excellent anti-icing, anti-corrosion, and self-cleaning characteristics. In this work, a superhydrophobic hydroxypropyl methylcellulose (HPMC)/SiO₂ coating is prepared using an efficient, fluorine-free method for the anti-icing application of transmission line insulators and other similar material surfaces. The water contact angle (WCA) of the coating is 161°, and the slide angle (SA) is less than 1°. The coating maintains good hydrophobicity after mechanical durability tests. In the anti-icing performance tests, the start freezing time of a single droplet is delayed by 1366 s, and when the surface is not coated, the ice amount is more than twice that with the coating. Therefore, this work provides a straightforward and promising solution to solving high-cost and low-efficiency difficulties in the anti-icing problem of transmission line insulators and other similar material surfaces.

Design of Multi-Functional Superhydrophobic Coating via Bacterium-Induced Hierarchically Structured Minerals on Steel Surface

The fabrication of an eco-friendly, multi-functional, and mechanically robust superhydrophobic coating using a simple method has many practical applications. Here, inspired by shell nacre, the micro- or nano-scale surface roughness that is necessary for superhydrophobic coatings was formed via Bacillus subtilis–induced mineralization. The biomineralized film coated with hexadecyltrimethoxysilane (HDTMS) exhibited superhydrophobicity with water contact angles of 156°. The biomimetic HDTMS/calcite-coating showed excellent self-cleaning, anti-icing, and anti-corrosion performances. Furthermore, mechanically robust superhydrophobicity could be realized by hierarchically structured biomineralized surfaces at two different length scales, with a nano-structure roughness to provide water repellency and a micro-structure roughness to provide durability. Our design strategy may guide the development of “green” superhydrophobic coatings that need to retain effective multi-functional abilities in harsh marine environments.

Icephobic/anti-icing properties of superhydrophobic surfaces

In the winter, icing on solid surfaces is a typical occurrence that may create a slew of hassles and even tragedies. Anti-icing surfaces are one of the effective solutions for this kind of problem. The roughness of a superhydrophobic surface traps air and weakens the contact between the solid surface and liquid water, allowing water droplets to be removed before freezing. At present, the conventional anti-icing methods including mechanical or thermal technology are not only surface structure unfriendly but also have the obsessions of low efficiency, high energy consumption and high manufacturing costs. Hence, developing a way to remove ice by just modifying the surface shape or chemical composition with a low surface energy is extremely desirable. Numerous attempts have been made to investigate the evolution of ice nucleation and icing on superhydrophobic surfaces under the direction of the ice nucleation hypothesis. In this paper, the research progress of ice nucleation in recent years is reviewed from theoretical and application. The icephobic surfaces are described using the wettability and classical nucleation theories. The benefits and drawbacks of anti-icing superhydrophobic surface are summarized, as well as deicing methods. Finally, several applications of ice phobic materials are illustrated, and some problems and challenges in the research field are discussed. We believed that this review will be useful in guiding future water freezing initiatives.

Advances in the development of superhydrophobic and icephobic surfaces

Superhydrophobicity and icephobicity are governed by surface chemistry and surface structure. These two features signify a potential advance in surface engineering and have recently garnered significant attention from the research community. This review aims to simulate further research in the development of superhydrophobic and icephobic surfaces in order to achieve their wide-spread adoption in practical applications. The review begins by establishing the fundamentals of the wetting phenomenon and wettability parameters. This is followed by the recent advances in modeling and simulations of the response of superhydrophobic surfaces to static and dynamic droplets contact and impingement, respectively. In view of their versatility and multifunctionality, a special attention is given to the development of these surfaces using nanocomposites. Furthermore, the review considers advances in icephobicity, its comprehensive characterization and its relation to superhydrophobicity. The review also includes the importance of the use of superhydrophobic surface to combat viral and bacterial contamination that exist in fomites.

Preparation strategy and evaluation method of durable superhydrophobic rubber composites

Superhydrophobic rubber composites have broad application prospects in national defense, industrial and agricultural production and daily life due to their special surface wettability. However, its poor durability at present seriously limits its practical application. Microstructure and low surface energy substances are the decisive factors to realize superhydrophobic surface. Therefore, three strategies to improve the durability of superhydrophobic surface were put forward, including improving the mechanical strength of microstructure, enhancing the adhesion between coating and substrate, and constructing self-repairing surface. On this basis, the preparation techniques of durable superhydrophobic rubber composites were summarized, and then the evaluation methods of durability of superhydrophobic rubber composites were introduced in detail from mechanical durability and chemical durability.

Gels as emerging anti-icing materials: a mini review

Gel materials have drawn great attention recently in the anti-icing research community due to their remarkable potential for reducing ice adhesion, inhibiting ice nucleation, and restricting ice propagation. Although the current anti-icing gels are in their infancy and far from practical applications due to poor durability, their outstanding prospect of icephobicity has already shed light on a new group of emerging anti-icing materials. There is a need for a timely review to consolidate the new trends and foster the development towards dedicated applications. Starting from the stage of icing, we first survey the relevant anti-icing strategies. The latest anti-icing gels are then categorized by their liquid phases into organogels, hydrogels, and ionogels. At the same time, the current research focuses, anti-icing mechanisms and shortcomings affiliated with each category are carefully analysed. Based upon the reported state-of-the-art anti-icing research and our own experience in polymer-based anti-icing materials, suggestions for the future development of the anti-icing gels are presented, including pathways to enhance durability, the need to build up the missing fundamentals, and the possibility to enable stimuli-responsive properties. The primary aim of this review is to motivate researchers in both the anti-icing and gel research communities to perform a synchronized effort to rapidly advance the understanding and making of gel-based next generation anti-icing materials.

Anisotropic Janus materials: from micro-/nanostructures to applications

Janus materials have led to great achievements in recent years owing to their unique asymmetric structures and properties. In this review, recent advances of Janus materials including Janus particles and Janus membranes are summarized, and then the microstructures and applications of Janus materials are emphasized. The asymmetric wettability of Janus materials is related to their microstructures; hence, the microstructures of Janus materials were analyzed, compared and summarized. Also presented are current and potential applications in sensing, drug delivery, oil-water separation and so on. Finally, a perspective on the research prospects and development of Janus materials in more fields is given.

Designing Self-Sustainable Icephobic Layer by Introducing a Lubricating Un-Freezable Water Hydrogel from Sodium Polyacrylate on the Polyolefin Surface

A convenient, environment-friendly, and cost-effective method to keep anti-icing for a long time was highly desirable. Slippery lubricant layers were regarded to be effective and promising for anti-icing on different surfaces, but the drought-out of lubricants and the possible detriments to the environment were inevitable. By combining super-high molecular weight sodium polyacrylate (H-PAAS) with polyolefin through a one-pot method, a self-sustainable lubricating layer with extremely low ice adhesion of un-freezable water hydrogel was achieved at subzero conditions. The lubricant hydrogel layer could auto-spread and cover the surface of polyolefin after encountering supercooled water, frost, or ice. Due to the reduction of storage modulus in the interface, the ice adhesion of the specimen surfaces was far below 20 kPa, varying from 5.13 kPa to 18.95 kPa. Furthermore, the surfaces could preserve the fairly low adhesion after icing/de-icing cycles for over 15 times and thus exhibited sustainable durability. More importantly, this method could be introducing to various polymers and is of great promise for practical applications.

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.

Superhydrophobic, superamphiphobic and SLIPS materials as anti-corrosion and anti-biofouling barriers

Multifunctional interfacial materials with special wettability including superhydrophobic, superamphiphobic, and SLIPS exhibited promising potentials for corrosion and biofouling resistance.

Thermally Induced Gradient of Properties on a Superhydrophobic Magnesium Alloy Surface

Fabrication of superhydrophobic coatings for magnesium alloys is in high demand for various industrial applications. Such coatings not only extend the service life of metal structures, but also impart additional useful functional properties to the coated surface. In this study, we show that nanosecond laser processing of long, thin stripes of magnesium alloys followed by the deposition of a hydrophobic agent onto the magnesium oxide layer is a simple, convenient, and easily reproducible method for obtaining superhydrophobic surfaces with property gradient along the sample. The mechanism of the gradient in wettability and electrochemical properties of the magnesium alloy surface is discussed based on the high-temperature growth of magnesium oxide and its following degradation. The latter is related to the development of internal stresses and the formation of cracks and pores within the oxide layer at prolonged exposure to high temperatures during the interaction of a laser beam with the substrate. The effect of heating during laser processing of magnesium materials with limited sizes on the protective properties of the forming coatings is elucidated.

Clarifying the Correlation of Ice Adhesion Strength with Water Wettability and Surface Characteristics

Although icephobic surfaces have been extensively investigated in the past decades, a controversy remains on the relationship between water repellency and ice repellency. Little insight has been truly obtained on the dependence of ice adhesion on the surface/interface characteristics because of the limited range of these characteristics that have been investigated in the past. In this study, we prepared 37 coatings with a wide range of surface characteristics. The measured ice adhesion strength was discussed in correlation with water wettability and surface topological parameters. It was verified that parameters related to water wettability, such as water contact angle, contact angle hysteresis, and an index of work of adhesion with water, (1 + cos θ_rec), do not have a simple correlation with ice adhesion strength. Thus, they should not be used as a design parameter for low icephobic surfaces. The current study points out that the study of surface texture should be carried out in conjunction with surface chemistry/energy consideration. Without control of the surface chemistry, the correlation between surface texture parameters will lead to inconsistent conclusions because of the uncertainty of the contact mode. Our investigation indicates that low ice adhesion strength (<50 kPa) is attainable with a smooth surface (root-mean-squared roughness < 50 nm) when a low surface energy (<15 mJ/m²) is maintained. This finding opens a new paradigm for the design of icephobic coatings away from the conventional practices of using superhydrophobic and oil-infused surfaces.

Droplet Impact on the Cold Elastic Superhydrophobic Membrane with Low Ice Adhesion

The elastic membranes with different surface stiffness were fabricated via spin-coating followed by the laser ablation. The as-fabricated elastic membrane exhibited superhydrophobicity with a rough microstructure. The droplet impacting experiment on the cold elastic superhydrophobic membrane was conducted, and the influence of surface stiffness and impacting speed on the droplet impacting process were investigated. It was found that the elastic superhydrophobic membrane exhibits a robust anti-icing performance compared with the elastic hydrophobic membrane. A lower surface stiffness corresponds to a larger deformation degree of the elastic membrane and to a smaller maximum droplet spreading diameter. Moreover, the contact time decreases with the increase of impacting speed as for the same stiffness of the cold elastic superhydrophobic membrane. The underlying mechanism of the cold elastic membrane with low ice adhesion may be due to the face that the deformation of the superhydrophobic membrane provides an elastic force for the droplet to detach from the surface and thus reduce the heat transfer between the droplet and the surface.

Water and Ice Adhesion to Solid Surfaces: Common and Specific, the Impact of Temperature and Surface Wettability

Ice adhesion plays a crucial role in the performance of materials under outdoor conditions, where the mitigation of snow and ice accumulation or spontaneous shedding of solid water precipitations are highly desirable. In this brief review we compare the adhesion of water and ice to different surfaces and consider the mechanisms of ice adhesion to solids basing on the surface forces analysis. The role of a premelted or quasi-liquid layer (QLL) in the ice adhesion is discussed with the emphasis on superhydrophobic surfaces, and the temperature dependence of ice adhesion strength is considered with an account of QLL. We also very briefly mention some recent methods for the measurement of ice adhesion strength to the icephobic engineering materials outlining the problems which remain to be experimentally solved.

A superhydrophobic surface with aging resistance, excellent mechanical restorablity and droplet bounce properties

The use of a silicone rubber composite insulator has become an important aspect to ensure the safe operation of an electrical power grid. This study introduces a preparation method of a superhydrophobic silicone rubber surface using a simple preparation process at low cost and with excellent performance, which can be used in the mass production of silicone rubber composite insulators. In this study, the combination of a compression molding process and a template method was used to prepare the product. A microstructure composed of numerous boat-shaped grooves was constructed on the surface of silicone rubber. The modification of a low surface energy material is not required. The static contact angle with water after the high-temperature treatment exceeds 150°, and the rolling angle is under 10°. Excellent performance has been observed in terms of self-cleaning effect, aging resistance, and mechanical and droplet bounce properties. It has been shown that the loss of superhydrophobic properties, due to the prolonged immersion in water, can be restored by a high temperature heating process.

Novel porous oil-water separation material with super-hydrophobicity and super-oleophilicity prepared from beeswax, lignin, and cotton

The traditional fluorinated porous material with super-hydrophobicity and super-oleophilicity is an effective strategy for oil-water separation. However, in recent years, fluorinated materials have been classified as "Emerging Environmental Pollutants" by U. S. Environmental Protection Agency because of difficult degradation and bio-accumulation. It is unacceptable to introduce new pollutants while solving environmental disasters. Therefore, it is great requirement to explore a low-cost, environmentally friendly, and renewable technique for the fabrication of novel porous materials with super-hydrophobicity and super-oleophilicity to separate oil-water mixtures. In this work, renewable beeswax, lignin, and cotton have been chosen to prepare the biomass-based porous materials with super-hydrophobicity and super-oleophilicity for oil-water separation. The mixture of beeswax and lignin is modified on the surface of cotton to obtain the biomass-based porous materials with super-hydrophobicity and super-oleophilicity. The beeswax and lignin provide low surface energy and micro/nanoscale structures, respectively. The introduction of lignin effectively improves the thermal stability of the porous materials. The apparent contact angle still remains to be above 150° after a long-time heating. The porous materials effectively separate oil-water mixtures and have good absorption effect for heavy oil (density greater than water). Moreover, the porous materials are easily recyclable after reactivation. This strategy of preparing oil-water separation materials from renewable natural polymers not only helps to clean the environment, but also helps to recover valuable oil.

Rapid fabrication of a dual-scale micro-nanostructured superhydrophobic aluminum surface with delayed condensation and ice formation properties

Aluminum (Al) is widely used in all forms of industry, including automobile, aerospace, transmission lines, and exchangers, and in general household appliances. Ice accumulation on Al surfaces may cause serious problems, especially during the winter, leading to critical damage to mechanical systems. In this study, we developed a superhydrophobic coating with anti-icing properties on an Al surface using a simple and cost-effective technique. The superhydrophobic dual-shape micro-/nanostructured (MN-) Al surface was fabricated by a facile chemical etching and an anodization method, followed by surface modification with polydimethylsiloxane (PDMS) via a simple thermal vapor deposition method. The static contact angle of the fabricated surface was more than 160 °C. Compared with the bare surface and the silicone oil-infused PDMS coating (SLIPS) on the MN-structured Al substrate, the fabricated superhydrophobic surface displayed excellent anti-icing. Ice formation on the superhydrophobic surface was delayed by 80 and 45 min at -5 °C and -10 °C, respectively, at a relative humidity of 80% ± 5%. The superhydrophobic surface demonstrated an increase of almost four and two times delay in icing time on the surface over bare and SLIPS surfaces, respectively. The coalescence induced jumping behavior of condensate water droplets was also investigated on the fabricated surfaces. The result indicates that the superhydrophobic surface can effectively delay ice/frost formation by the synergetic effect of surface morphology and the extremely low adhesive property of the surfaces, which allows the self-propelled jumping phenomenon at low temperature and high humidity. This proposed simple, fast, and cost-effective method could be applied to design large-scale anti-icing surfaces.

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).

Spraying Fabrication of Durable and Transparent Coatings for Anti-Icing Application: Dynamic Water Repellency, Icing Delay, and Ice Adhesion

Anti-icing/icephobic coatings, typically applied in the form of surface functional materials, are considered to be an ideal selection to solve the icing issues faced by daily life and industrial production. However, the applications of anti-icing coatings are greatly limited by the two main challenges: bonding strength with substrates and stability of the high anti-icing performance. Here, we designed and fabricated a kind of high-performance superhydrophobic fluorinated silica (F-SiO₂)@polydimethylsiloxane coatings and further emphasized the improvement of the bonding strength with substrates and the maintenance of high anti-icing performance. The resultant coatings exhibited excellent water repellency with a contact angle up to 155.3° and a very short contact time (∼10.2 ms) of impact droplets. At low temperatures, the coming droplets still rapidly rebounded off the coating surface, and the superhydrophobic coatings displayed a more than 50-fold increase of freezing time comparing with bare aluminum. The ice adhesion strength on the coatings was only 26.3 kPa, which was far less than that (821.9 kPa) of bare aluminum. Furthermore, the nanoporous structures constructed by anodic oxidation could tremendously enhance the bonding strength of the coatings with the substrate, which was evaluated through a standard method (ASTM D3359). The anti-icing properties still retained high stability under the conditions of 30 icing/deicing cycles, soaking, and scouring of acid solution (pH = 5.6). This work can effectively push the anti-icing coatings toward a real-world application.

Facile synthesis of superhydrophobic three-metal-component layered double hydroxide films on aluminum foils for highly improved corrosion inhibition

A simple hydrothermal method was presented to obtain various superhydrophobic ZnMgAl layered double hydroxide films on aluminum foils (AF) with excellent corrosion inhibition.

Icephobic Strategies and Materials with Superwettability: Design Principles and Mechanism

Ice formation and accretion on surfaces is a serious economic issue in energy supply and transportation. Recent strategies for developing icephobic surfaces are intimately associated with superwettability. Commonly, the superwettability of icephobic materials depends on their surface roughness and chemical composition. This article critically categorizes the possible strategies to mitigate icing problems from daily life. The wettability and classical nucleation theories are used to characterize the icephobic surfaces. Thermodynamically, the advantages/disadvantages of superhydrophobic surfaces are discussed to explain icephobic behavior. The importance of elasticity, slippery liquid-infused porous surfaces (SLIPSs), amphiphilicity, antifreezing protein, organogels, and stimuli-responsive materials has been highlighted to induce icephobic performance. In addition, the design principles and mechanism to fabricate icephobic surfaces with superwettability are explored and summarized.

Totally Waterborne, Nonfluorinated, Mechanically Robust, and Self-Healing Superhydrophobic Coatings for Actual Anti-Icing

Bioinspired superhydrophobic coatings are of great interest in academic and industrial areas. However, their real-world applications are hindered by some main bottlenecks, especially the pollutive preparation methods (e.g., organic solvents and fluorinated compounds) and poor mechanical stability. Here, we report for the first time the totally waterborne, nonfluorinated, mechanically robust, and self-healing superhydrophobic coatings. The coatings were fabricated by spray-coating polyurethane (PU) aqueous solution and a hexadecyl polysiloxane-modified SiO₂ (SiO₂@HD-POS) aqueous suspension onto substrates using PU as the adhesive. The SiO₂@HD-POS suspension was synthesized by HCl-catalyzed reactions among hexadecyltrimethoxysilane, tetraethoxysilane, and SiO₂ nanoparticles. Besides high superhydrophobicity, the coatings exhibit exceptional mechanical stability against sandpaper abrasion for 200 cycles at 9.8 kPa and tape-peeling for 200 cycles at 90.5 kPa because of high durability and unique hierarchical macro-/nanostructure of the coating as well as solid lubrication of the SiO₂@HD-POS nanoparticles fallen off from the coatings. The coatings also show fast and stable self-healing capability owing to migration of the healing agent (HD-POS) to the damaged surface. Moreover, the coatings exhibit good static and dynamic anti-icing performance in outdoor environment (-15 °C, relative humidity = 54%). The superhydrophobic coatings may be used in various areas because the main bottlenecks have been successfully broken.

Tunable superamphiphobic surfaces: a platform for naked-eye ATP detection

A superamphiphobic surface composed of two different size ranges of TiO₂ nanoparticles was simply fabricated through spraying the perfluorosilane coated TiO₂ nanoparticles suspension dispersing in ethanol. The surface chemistry was finely regulated through gradient UV irradiation-induced organic compound degradation to fabricate surface with gradient solid surface energy or wettability. The fabricated surface shows good droplet sorting ability, which can successfully discriminate ethanol droplets with different concentrations. As a proof-of-concept, the biosensor application of this surface was demonstrated by using it for naked-eye ATP detection. Liquid droplets with different concentrations of ATP after ATP-dependent rolling circle amplification (RCA) can be effectively sorted by the surface. This developed biosensor methodology based on droplet sorting ability of the fabricated surface is energy-efficient and economical which is promising for biosensors, point-of-care testing, and biochemical assays. Graphical abstract ᅟ.

Biomimetic self-slippery and transferable transparent lubricant-infused functional surfaces

Self-slippery liquid-infused porous surfaces (SLIPSs) have been presented owing to their enormous number of potential applications and have widely attracted the attention of researchers in recent years. In comparison with superhydrophobic surfaces, SLIPSs not only exhibit interfacial performance that corresponds to superhydrophobicity but also do not require the construction of a complicated and delicate morphology. Here, a facile strategy has been proposed for constructing silica SLIPSs. Three common lubricants (perfluoropolyethers, liquid paraffin and ethyl oleate) were employed in this study. Using a facile brush process, the surface can be coated on a substrate, and, after infusion of the lubricant, the transformation from superhydrophobicity to self-slippage properties can be achieved. In addition, changing the kind of lubricant and adjusting the amount of nanoscale hybrid silica particles in the coating solution can modulate the surface transparency and interfacial characteristics, which makes the surface meet the various requirements of different service conditions. This transferable performance endows the surface with the possibility of meeting the various requirements of different conditions and demonstrates the enormous value of the application of the coatings in many fields.

Fabrication of Superhydrophobic AA5052 Aluminum Alloy Surface with Improved Corrosion Resistance and Self Cleaning Property

The development of a self-cleaning and corrosion resistant superhydrophobic coating for aluminum alloy surfaces that is durable in aggressive conditions has attracted great interest in materials science. In the present study, a superphydrophobic film was fabricated on an AA5052 aluminum alloy surface by the electrodeposition of Ni–Co alloy coating, followed by modification with 6-(N-allyl-1,1,2,2-tetrahydro-perfluorodecyl) amino-1,3,5-triazine-2,4-dithiol monosodium (AF17N). The surface morphology and characteristics of the composite coatings were investigated by means of scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), atomic force microscope (AFM) and contact angle (CA). The corrosion resistance of the coatings was assessed by electrochemical tests. The results showed that the surface exhibited excellent superhydrophobicity and self-cleaning performance with a contact angle maintained at 160° after exposed to the atmosphere for 240 days. Moreover, the superhydrophobic coatings significantly improved the corrosion resistant performance of AA5052 aluminum alloy substrate in 3.5 wt.% NaCl solution.

Anti-icing Properties on Surfaces through a Functional Composite: Effect of Ionic Salts

This study reports the potential of a unique functional composite for anti-icing applications. To date, various ionic salt formulations have been applied to prevent ice accumulation on surfaces. However, salt can be removed by external factors and large amounts must be used to attain anti-icing properties. Incorporating hydrophilic salts into hydrophobic mediums and controlled release of specific agents can provide effective solution to reduce ice accumulation on surfaces. Here, we developed functional polymer composites with salt pockets of altered ionic salts consisting of potassium formate (KCOOH), sodium chloride (NaCl), or magnesium chloride (MgCl₂). We dissolved ionic salts in hydrophilic gel domains and dispersed in a hydrophobic styrene-butadiene-styrene polymer matrix. Na⁺ and Cl^- ions delayed ice formation by 42.6 min at -2 °C compared to that for unmodified surfaces. Functional composites prepared with the NaCl ionic salt exhibited better anti-icing behavior at -2 °C because of their high concentration compared to that of the composites prepared with KCOOH and MgCl₂ ionic salts. We also characterized the release of ionic salts from composite-modified hydrophobic medium separately up to 118 days. Furthermore, we monitored freezing of water on composite-incorporated or composite-coated hydrophobic surfaces in a camera-integrated cold chamber with a uniform temperature (-2 °C). The results demonstrated significant increases in the delay of freezing on composite-incorporated or composite-coated surfaces compared to that on controls. We observed altered effects of each ionic salt on the mechanical, morphological, and functional properties of the composite-incorporated or composite-coated hydrophobic surfaces. Our results suggested that the efficiency of a polymer composite to promote anti-icing behavior on a surface is directly related to the type and concentration of the particular ionic salt incorporation into the composite. This approach is promising and demonstrates significant potential of the ionic salt embedded within polymer composite-modified hydrophobic surfaces to attain delayed icing function.