Large-Area Preparation of Robust and Transparent Superomniphobic Polymer Films

Surface Repellency beyond Hydrophobicity: A Review on the Latest Innovations in Superomniphobic Surfaces

Superhydrophobic surfaces have long faced challenges in repelling low-surface-tension liquids like oil and alcohol, limiting their practical applications. Over the past few years, researchers have been actively looking for new alternatives to overcome this issue. Recently, superomniphobic surfaces have attracted significant interest due to their ability to repel both high- and low-surface-tension liquids. Compared with superhydrophobic surfaces, superomniphobic surfaces provide enhanced liquid repellency, making them more suitable for industrial and real-world applications. This Review explores the recent advancements in the fabrication of superomniphobic surfaces. Three basic wetting principles, Young's, Wenzel's, and Cassie-Baxter's equations, are discussed. The vital role of low surface energy and high surface roughness of hierarchical and re-entrant structures in achieving a steady Cassie-Baxter state that has a low contact area between the solid surface and liquid droplet is emphasized. Additionally, a comprehensive description of various fabrication techniques, characterizations, and practical applications of superomniphobic surfaces is provided. Finally, the challenges and future prospects regarding this research area are addressed. This comprehensive review aims to inspire researchers to refine and enhance current development methods of superomniphobic surfaces and stimulate further exploration in the research field.

Highly Transparent Superhydrophobic Coatings for Prevention of Raindrop Adhesion on Rearview Mirrors

The adhesion of raindrops on car rearview mirrors poses a significant threat to traffic safety due to the resulting blurred vision. Transparent superhydrophobic coatings have emerged as a potential solution to this problem. However, the development of transparent superhydrophobic coatings is often hampered by complex preparation procedures, high costs, and limited substrate compatibility, rendering them unsuitable for practical applications. Herein, we present a facile spraying method for fabricating a transparent superhydrophobic perfluorodecyl polysiloxane-modified silica (SiO2@FD-POS) coating with a high transparency of approximately 91%, which is comparable to that of bare glass (∼93%). This coating can be applied onto various substrates, including paper, polycarbonate goggles, and PET fabric, without altering their inherent color. Furthermore, the SiO2@FD-POS coating demonstrates robust mechanical, thermal, and UV durabilities, which are crucial for its application in outdoor conditions. When applied to a rearview mirror, this coating effectively prevents raindrops from adhering on the surface for over 60 min during moderate rainfall, maintaining a clear reflection throughout. Therefore, the SiO2@FD-POS coating holds significant potential in enhancing drivers' visibility during rainy conditions, thus contributing to high driving safety.

Dragonfly-Inspired Transparent Superhydrophobic Coatings with Low Haze and High Mechanical Robustness

Transparent superhydrophobic coatings hold significant potential for applications such as windows and reflectors. However, issues such as fragility and high haze have limited their practicality. Drawing inspiration from dragonfly structures, we developed a transparent superhydrophobic coating by etching the polystyrene microsphere array semiembedded on a silicon oxide matrix and subsequently depositing the methyltrichlorosilane-derived nanofilaments. The resulting coating features silicon oxide craters and nanofilaments inspired by dragonfly wings. Due to the coating's small, multiscale nanostructures, it has a high average visible light transmittance of 90.4% and a low average haze of 4.0%, comparable to the substrate glass. It also exhibits exceptional superhydrophobic properties, with a contact angle of 161.5° and a sliding angle of 1.5°. Notably, the coating retains its superhydrophobicity even after withstanding impacts from 5 kg of water and 500 g of sand, thanks to its robust wing vein-inspired protected structure. Additionally, it shows strong resistance to acids, alkalis, and temperatures up to 400 °C. The coating maintains a high transmittance and low haze after 67 days of UV irradiation or 300 days of outdoor exposure. The combination of low haze and robustness in this transparent superhydrophobic coating highlights its promising potential for applications in related fields.

Bioinspired Slippery Surfaces for Liquid Manipulation from Tiny Droplet to Bulk Fluid

Slippery surfaces, which originate in nature with special wettability, have attracted considerable attention in both fundamental research and practical applications in a variety of fields due to their unique characteristics of superlow liquid friction and adhesion. Although research on bioinspired slippery surfaces is still in its infancy, it is a rapidly growing and enormously promising field. Herein, a systematic review of recent progress in bioinspired slippery surfaces, beginning with a brief introduction of several typical creatures with slippery property in nature, is presented. Subsequently,this review gives a detailed discussion on the basic concepts of the wetting, friction, and drag from micro- and macro-aspects and focuses on the underlying slippery mechanism. Next, the state-of-the-art developments in three categories of slippery surfaces of air-trapped, liquid-infused, and liquid-like slippery surfaces, including materials, design principles, and preparation methods, are summarized and the emerging applications are highlighted. Finally, the current challenges and future prospects of various slippery surfaces are addressed.

Regenerated SERS substrate based on Ag/AuNPs-TiO2-oxidized carbon cloth for detection of imidacloprid

Imidacloprid (IMI) are widely used in modern tea industry for pest control, but IMI residues pose a great threat to human health. Herein, we propose a regeneration metal-semiconductor SERS substrate for IMI detection. We fabricated the SERS sensor through the in-situ growth of a nano-heterostructure incorporating a semiconductor (TiO2) and plasmonic metals (Au, Ag) on oxidized carbon cloth (OCC). Leveraging the high-density hot spots, the formed Ag/AuNPs-TiO2-OCC substrate exhibits higher enhancement factors (1.92 × 108) and uniformity (RSD = 7.68%). As for the detection of IMI on the substrate, the limit of detection was lowered to 4.1 × 10-6 μg/mL. With a hydrophobic structure, the Ag/AuNPs-TiO2-OCC possessed excellent self-cleaning performance addressing the limitation of single-use associated with traditional SERS substrates, as well as the degradation capability of the substrate under ultraviolet (UV) light. Accordingly, Ag/AuNPs-TiO2-OCC showcases outstanding SERS sensing and regenerating properties, making it poised for extensive application in the field of food safety assurance.

Off-Stoichiometry Thiol-Ene (OSTE) Micro Mushroom Forest: A Superhydrophobic Substrate

Superhydrophobic surfaces have been used in various fields of engineering due to their resistance to corrosion and fouling and their ability to control fluid movement. Traditionally, superhydrophobic surfaces are fabricated via chemical methods of changing the surface energy or mechanical methods of controlling the surface topology. Many of the conventional mechanical methods use a top-to-bottom scheme to control the surface topolopy. Here, we develop a novel fabrication method of superhydrophobic substrates using a bottom-to-top scheme via polymer OSTE, which is a prototyping polymer material developed for the fabrication of microchips due to its superior photocuring ability, mechanical properties, and surface modification ability. We fabricate a superhydrophobic substrate by OSTE-OSTE micro mushroom forest via a two-step lithography process. At first, we fabricate an OSTE pillar forest as the mushroom stems; then, we fabricate the mushroom heads via backside lithography with diffused UV light. Such topology and surface properties of OSTE render these structures superhydrophobic, with water droplets reaching a contact angle of 152.9 ± 0.2°, a sliding angle of 4.1°, and a contact angle hysteresis of less than 0.5°. These characteristics indicate the promising potential of this substrate for superhydrophobic applications.

Pinning Forces on the Omniphobic Dry, Liquid-Infused, and Liquid-Attached Surfaces

Omniphobic coatings effectively repelling water, oils, and other liquids are of great interest and have a broad number of applications including self-cleaning, anti-icing surfaces, biofouling protection, selective filtration, etc. To create such coatings, one should minimize the pinning force that resists droplet motion and causes contact angle hysteresis. The minimization of the free surface energy by means of the chemical modification of the solid surface is not enough to obtain a nonsticky slippery omniphobic surface. One should minimize the contact between the solid and the droplet. Besides coating the surface with flat polymer films, among the major approaches to create omniphobic coatings, one can reveal "lotus effect" textured coatings, slippery liquid-infused porous surfaces (SLIPS), and slippery omniphobic covalently attached liquid (SOCAL) coatings. It is possible to turn one surface type into other by texturizing, impregnating with liquids, or grafting flexible liquid-like polymer chains. There are a number of models describing the pinning force on surfaces, but the transitions between states with different wetting regimes remain poorly understood. At the same time, such studies can significantly broaden existing ideas about the physics of wetting, help to design coatings, and also contribute to the development of generalized models of the pinning force. Here we review the existing pinning force (contact angle hysteresis) models on various omniphobic substrates. Also, we discuss the current studies of the pinning force in the transitions between different wetting regimes.

Rational Design of Highly Comprehensive Liquid-Like Coatings with Enhanced Transparency, Concerted Multi-Function, and Excellent Durability: A Ternary Cooperative Strategy

Durable repellent surfaces of high transparency find key applications in daily life and industry. Nevertheless, developing anti-reflective coatings with omni-repellency, concerted multi-function, and desirable durability remains a daunting challenge. Here, a highly comprehensive coating is designed based on the combination of structural design and molecular design. The resulting silica hybrid coating not only manifests enhanced transparency and exceptional omniphobicity, but also achieves integration of multi-function (e.g., anti-smudge, anti-icing, and anti-corrosion). The unprecedented durability of the coating is evidenced by maintaining slipperiness after rigorous treatments, such as 2.5 × 105-cycle mechanical abrasion with a high loading pressure of 100 kPa, 1000-cycle adhesion/peeling and soaking in extreme pH solutions, etc. This work provides a design blueprint for manufacturing versatile and durable coatings for wide-ranging applications.

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

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

Enhancing biomass production and biochemical compositions of Spirodela polyrhiza through superhydrophobic cultivation platforms at low light intensity

Duckweed, a floating macrophyte, has attracted interest in various fields such as animal feedstocks and bioenergy productions. Its enriched nutritional content and rapid growth rate make it particularly promising. However, common laboratory cultures of duckweed often experience fronds layering, diminishing the efficiency of sunlight capturing due to limited surface area on conventional cultivation platforms. In this work, we aimed to address the issue of fronds layering by introducing a novel cultivation platform - a superhydrophobic coated acrylic sheet. The sheet was prepared by spray-coating a suspension of beeswax and ethanol, and its effectiveness was evaluated by comparing the growth performance of giant duckweed, Spirodela polyrhiza, on this platform with that on a modified version. The superhydrophobic coated acrylic sheet (SHPA) and its variant with a metal mesh added (SHPAM) were employed as growing platforms, with a glass jar serving as the control. The plantlets were grown for 7 days with similar growth conditions under low light stress (25 μmol/m2/s). SHPAM demonstrated superior growth performance, achieving a mass gain of 102.12 ± 17.18 %, surpassing both SHPA (89.67 ± 14.97 %) and the control (39.26 ± 8.94 %). For biochemical compositions, SHPAM outperformed in chlorophyll content, protein content and lipid content. The values obtained were 1.021 ± 0.076 mg/g FW, 14.59 ± 0.58 % DW and 6.21 ± 0.75 % DW respectively. Therefore, this work proved that incorporation of superhydrophobic coatings on a novel cultivation platform significantly enhanced the biomass production of S. polyrhiza. Simultaneously, the biochemical compositions of the duckweeds were well-maintained, showcasing the potential of this approach for optimized duckweed cultivation.

Transparent anti-fingerprint glass surfaces: comprehensive insights into theory, design, and prospects

With the advancement of information technology, touch-operated devices such as smartphones, tablets, and computers have become ubiquitous, reshaping our interaction with technology. Transparent surfaces, pivotal in the display industry, architecture, and household appliances, are prone to contamination from fingerprints, grease, and dust. Such contaminants compromise the cleanliness, aesthetic appeal, hygiene of the glass, and the overall user visual experience. As a result, fingerprint prevention has gained prominence in related research domains. This article delves into the primary characteristics of fingerprints and elucidates the fundamental mechanisms and components behind their formation. We then explore the essential properties, classifications, and theoretical foundations of anti-fingerprint surfaces. The paper concludes with a comprehensive review of recent advancements and challenges in transparent superlyophobic fingerprint-resistant surfaces, projecting future trajectories for transparent fingerprint-resistant glass surfaces.

Porous polydimethylsiloxane films with specific surface wettability but distinct regular physical structures fabricated by 3D printing

Porous polydimethylsiloxane (PDMS) films with special surface wettability have potential applications in the biomedical, environmental, and structural mechanical fields. However, preparing porous PDMS films with a regular surface pattern using conventional methods, such as chemical foaming or physical pore formation, is challenging. In this study, porous PDMS films with a regular surface pattern are designed and prepared using 3D printing to ensure the formation of controllable and regular physical structures. First, the effect of the surface wettability of glass substrates with different surface energies (commercial hydrophilic glass and hydrophobic glass (F-glass) obtained by treating regular glass with 1H,1H,2H,2H-perfluorooctyl-trichlorosilane) on the structural characteristics of the 3D printed PDMS filaments is investigated systematically. Additionally, the effect of the printing speed and the surface wettability of the glass substrate on the PDMS filament morphology is investigated synchronously. Next, using the F-glass substrate and an optimized printing speed, the effects of the number of printed layers on both the morphologies of the individual PDMS filaments and porous PDMS films, and the surface wettability of the films are studied. This study reveals that regularly patterned porous PDMS films with distinct structural designs but the same controllable surface wettability, such as anisotropic surface wettability and superhydrophobicity, can be easily fabricated through 3D printing. This study provides a new method for fabricating porous PDMS films with a specific surface wettability, which can potentially expand the application of porous PDMS films.

A novel cultivation platform of duckweed (Lemna minor) via application of beeswax superhydrophobic coatings

Conventional establishment of laboratory cultures of duckweed Lemna minor are prepared in beakers, Erlenmeyer flasks or Schott bottles. These conventional cultivation methods limit the available surface area for growth which then causes layering of fronds that reduces the efficiency of plants in sunlight capturing. Here, acrylic sheets were spray-coated with a superhydrophobic (SHP) beeswax suspension and these coated acrylic sheets were used as a novel cultivation platform for L. minor. L. minor was grown for 7 days in conventional glass jar which acted as the control and were compared to SHP coated acrylic (SHPA) and SHP coated acrylic with aluminium mesh centrally placed (SHPAM) at similar duration and cultivation conditions. Addition of mesh was to entrap the plantlets and fixed the plantlets' position on the growing platform. The effects of cultivation platforms on growth rate and biochemical compositions of L. minor were monitored. The highest biomass growth was obtained from SHPA cultivation where the relative growth rate (RGR) was 0.0909 ± 0.014 day^-1 and the RGR was 2.17 times higher than the control. Moreover, L. minor harvested from SHPA displayed the highest values in total protein content, total carbohydrates content and crude lipid percentage. The values were 156.04 ± 12.13 mg/g, 94.75 ± 9.02 mg/g and 7.09 ± 1.14% respectively. However, the control showed the highest total chlorophyll content which was 0.7733 ± 0.042 mg/g FW. Although SHPA obtained a slightly lower chlorophyll content than the control, this growing platform is still promising as it displayed the highest growth rate as well as other biochemical composition. Hence, this study proved that the proposed method that applied superhydrophobic properties in cultivation of L. minor provided a larger surface area for L. minor to grow, which then resulted in a greater biomass production while simultaneously maintaining the quality of the biochemical compositions of duckweeds.

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.

Whether and When Superhydrophobic/Superoleophobic Surfaces Are Fingerprint Repellent

Driven by the ever-increasing demand for fingerprint-resistant techniques in modern society, numerous researches have proposed to develop innovative antifingerprint coatings based on superhydrophobic/superoleophobic surface design. However, whether superhydrophobic/superoleophobic surfaces have favorable repellency to the microscopic fingerprint is in fact an open question. Here, we establish a reliable method that enables evaluating the antifingerprint capability of various surfaces in a quantitative way. We show that superhydrophobicity is irrelevant with fingerprint repellency. Regarding superoleophobic surfaces, two distinct wetting states of microscopic fingerprint residues, i.e., the “repellent” and the “collapsed” states, are revealed. Only in the “repellent” state, in which the fingerprint residues remain atop surface textures upon being pressed, superoleophobic surfaces can bring about favorable antifingerprint repellency, which correlates positively with their receding contact angles. A finger-deformation-dependent intrusion mechanism is proposed to account for the formation of different fingerprint wetting states. Our findings offer important insights into the mechanism of fingerprint repellency and will help the design of high-performance antifingerprint surfaces for diverse applications.

A Scalable Haze-Free Antireflective Hierarchical Surface with Self-Cleaning Capability

The lotus effect indicates that a superhydrophobic, self-cleaning surface can be obtained by roughening the topography of a hydrophobic surface. However, attaining high transmittance and clarity through a roughened surface remains challenging because of its strong scattering characteristics. Here, a haze-free, antireflective superhydrophobic surface that consists of hierarchically designed nanoparticles is demonstrated. Close-packed, deep-subwavelength-scale colloidal silica nanoparticles and their upper, chain-like fumed silica nanoparticles individually fulfill haze-free broadband antireflection and self-cleaning functions. These double-layered hierarchical surfaces are obtained via a scalable spraying process that permits precise control over the coating morphology to attain the desired optical and wetting properties. They provide a "specular" visible transmittance of >97% when double-side coated and a record-high self-cleaning capability with a near-zero sliding angle. Self-cleaning experiments on photovoltaic devices verify that the developed surfaces can significantly enhance power conversion efficiencies and aid in retaining pristine device performance in a dusty environment.

A versatile "3M" methodology to obtain superhydrophobic PDMS-based materials for antifouling applications

Fouling, including inorganic, organic, bio-, and composite fouling seriously affects our daily life. To reduce these effects, antifouling strategies including fouling resistance, release, and degrading, have been proposed. Superhydrophobicity, the most widely used characteristic for antifouling that relies on surface wettability, can provide surfaces with antifouling abilities owing to its fouling resistance and/or release effects. PDMS shows valuable and wide applications in many fields, and due to the inherent hydrophobicity, superhydrophobicity can be achieved simply by roughening the surface of pure PDMS or its composites. In this review, we propose a versatile "3M" methodology (materials, methods, and morphologies) to guide the fabrication of superhydrophobic PDMS-based materials for antifouling applications. Regarding materials, pure PDMS, PDMS with nanoparticles, and PDMS with other materials were introduced. The available methods are discussed based on the different materials. Materials based on PDMS with nanoparticles (zero-, one-, two-, and three-dimensional nanoparticles) are discussed systematically as typical examples with different morphologies. Carefully selected materials, methods, and morphologies were reviewed in this paper, which is expected to be a helpful reference for future research on superhydrophobic PDMS-based materials for antifouling applications.

Improving superamphiphobicity by mimicking tree-branch topography

when a droplet impacts on a superhydrophobic structured surface below a certain impact velocity, the droplet can bounce off completely from the surface. However, above such velocity a fraction of the droplet will pin on the surface. Surfaces capable of repelling water droplets are ubiquitous in nature or have been artificially fabricated. However, as the surface tension of the liquid is reduced, the capability of the surface to remain non-wetting gets hindered. Despite progress in previous research, the understanding and development of superamphiphobic surface to impacting low surface tension droplets remains elusive. It is proposed that multi-layer re-entrant like roughness can further enhance the anti-wetting properties also for low surface tension fluids. In this work, we produce patterned conical micro-structures with lateral nano-sized roughness. Furthermore, the droplet impact experiments are conducted on various surfaces with variable surface tensions (27 mN/m - 72 mN/m) by using droplets with different Weber numbers (2-170). We show that conical microstructures with lateral roughness mimicking tree-branches provides a surface topology capable of absorbing the force exerted by the droplet during the impact which prevents the droplet from pinning on the surface at higher impact velocity even for low surface tension droplets. Our study has significance for understanding the liquid interaction mechanism with the surface during the impact process and for the associated surface design considerations.

One-Step Covalent Surface Modification to Achieve Oil-Water Separation Performance of a Non-Fluorinated Durable Superhydrophobic Fabric

In this work, a durable superhydrophobic fabric was fabricated by a facile covalent surface modification strategy, in which the anchoring of 10-undecenoyl chloride (UC) onto the fabric through the esterification reaction and covalent grafting of n-dodecyl-thiol (DT) via thiol-ene click chemistry were integrated into one step. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) measurement results demonstrated that UC and DT were covalently grafted onto the fabric surface. The formed gully-like rough structure by the grafted UC and DT on the fabric surface together with the inherent microfiber structure, combined with the grafted low-surface-energy materials of UC and DT, gave the resultant modified DT-UC@fabric superhydrophobic performance. The superhydrophobic DT-UC@fabric was used for separation of oil-water mixtures; it exhibited high separation efficiency of more than 98%. In addition, it presented excellent durability against mechanical damage; even after 100 cyclic tape-peeling and abrasion tests, the DT-UC@fabric could preserve superhydrophobic performance, which was ascribed to the formed covalent interactions between the fabric surface and the grafted UC and DT. Therefore, this work provided a facile, efficient strategy for fabricating superhydrophobic composites with excellent durability, which exhibited a promising prospect in the application of self-cleaning and oil-water separation.

Transparent Super-Repellent Surfaces with Low Haze and High Jet Impact Resistance

Transparent superhydrophobic surfaces are of vital significance for rising applications in optoelectronics, outdoor displays, building windows, and so on. However, facile fabrication of surfaces combining stable superhydrophobicity and high transparency with particularly low haze remains a challenge. Here, we demonstrate a nonfluorinated hierarchical surface, simply prepared by sequential spraying of a primer of poly(ethylene-co-acrylic acid) (EAA) and silica nanoparticles (SiO₂). The resultant surface shows remarkable liquid repellency (e.g., an apparent contact angle of >160° and a sliding angle of <2° for honey) and high transparency (a transmittance of ∼91% and a haze of ∼6%). Especially, flexible EAA adhesive enables the surface to resist water impinging (up to ∼15.0 m s^-1, higher than the terminal velocities of raindrops) and mechanical damaging. This super-repellent surface also presents excellent UV and chemical stability, sustaining a superhydrophobic state upon UVA exposure for 60 days and acidic corrosion or oil contamination for 7 days. With multirobustness and scalability, our coatings show great potential in related fields.

Controllable Design of Bifunctional VO2 Coatings with Superhydrophobic and Thermochromic Performances

The structure and functions of natural organisms provide great inspirational sources for designing and manufacturing bionic coatings, which hold a distinguished scientific promise to tackle challenges facing humans. In this work, we report a facile and controllable approach to prepare various hexagonal periodic array VO₂ thin films by simply manipulating the speed of the dip-coating operation. The hexagonal cellular-structured VO₂ surface delivered the best thermochromic performance with a T_lum of 79.34% and a ΔT_sol of 9.87%. Impressively, superhydrophobic and thermochromic properties could be integrated into hexagonal semi-dome thin films (with a T_lum of 70.9%, a ΔT_sol of 9.3%, and a water contact angle of 150°) without any post-treatment by low-surface-energy chemicals, which hold considerable potential for application in multifunctional smart windows. Moreover, based on the Cassie-Baxter mode and finite-difference time-domain calculations, the dependence of the thermochromic and wettability performances on the VO₂ structure has been investigated in this study.

A structural polymer for highly efficient all-day passive radiative cooling

All-day passive radiative cooling has recently attracted tremendous interest by reflecting sunlight and radiating heat to the ultracold outer space. While some progress has been made, it still remains big challenge in fabricating highly efficient and low-cost radiative coolers for all-day and all-climates. Herein, we report a hierarchically structured polymethyl methacrylate (PMMA) film with a micropore array combined with random nanopores for highly efficient day- and nighttime passive radiative cooling. This hierarchically porous array PMMA film exhibits sufficiently high solar reflectance (0.95) and superior longwave infrared thermal emittance (0.98) and realizes subambient cooling of ~8.2 °C during the night and ~6.0 °C to ~8.9 °C during midday with an average cooling power of ~85 W/m² under solar intensity of ~900 W/m², and promisingly ~5.5 °C even under solar intensity of ~930 W/m² and relative humidity of ~64% in hot and moist climate. The micropores and nanopores in the polymer film play crucial roles in enhancing the solar reflectance and thermal emittance.

There still remains a big challenge in fabricating highly efficient and low-cost radiative coolers for all-day and all-climates. Here, the authors report a hierarchically structured polymethyl methacrylate film with a micropore array combined with random nanopores for highly efficient day- and nighttime passive radiative cooling.

Preparation of Edible Non-wettable Coating with Soybean Wax for Repelling Liquid Foods with Little Residue

Liquid food adhesion on containers has increased food waste and pollution, which could be effectively alleviated with a superhydrophobic surface. In this research, the superhydrophobic coating was fabricated with edible soybean wax on different substrates by a spraying method. The coated surface showed excellent superhydrophobicity due to its microstructure formed by self-roughening, which could repel a variety of viscous liquid food with the apparent contact angle of 159 ± 2°. The coated surface was still liquid-repellent after hot water immersion (45 °C), abrasion test with sandpaper, water impact, finger touch and immersion into yogurt. The liquid-repellent coating with soybean wax, which is natural and green, is promising for application in the food industry to reduce waste.

Fabrication of mechanically resistant superhydrophobic synthetic suede materials

Functionalization of synthetic suede materials with excellent superhydrophobicity can expand their application ranges. Superhydrophobic synthetic suede was obtained by coating with polydimethylsiloxane (PDMS) and octadecyltrichlorosilane (OTS). Utilizing the synthetic suede effect of the fibrous rough structures in combination with the low surface energy micro-nano rough structure on fibers resulting from PDMS and OTS, the surface was easily turned superhydrophobic with self-cleaning properties. Abrasion tests showed that the superhydrophobic synthetic suede has excellent superhydrophobic performance after more than 2000 severe abrasion tests. This research provides a facile strategy for the preparation of practical superhydrophobic synthetic suede materials.

Superomniphobic Silk Fibroin/Ag Nanowires Membrane for Flexible and Transparent Electronic Sensor

Superwetting surfaces that repel various liquids have been exciting for biomimetic research and have displayed versatile potential applications. Generally, superhydrophobic coatings can allow for droplet rolling off and antifouling, whereas it is a challenge to achieve superomniphobic surfaces with transparency, flexibility, and conductivity. Here, we adopt an effective and simple method to fabricate a superomniphobic, transparent, and flexible smart silk fibroin (SF) membrane by spray-coating long AgNWs dispersed in polydimethylsiloxane (PDMS), followed by treatment with vacuum drying. The resulting SF/AgNWs membranes are super-repellent to different liquids with low surface tension and water, and demonstrate high contact angles (CAs) more than 150° and low rolling-off angles (RAs) even less than 10°. Moreover, the obtained membranes display superior sensitivity under stretching and bending, as well as intact stability of high transparency, which can be considered as promising flexible sensing electronics to detect human motions under wet conditions.

The fabrication of mechanically durable and stretchable superhydrophobic PDMS/SiO2 composite film

Stretchable superhydrophobic film was fabricated by casting silicone rubber polydimethylsiloxane (PDMS) on a SiO₂ nanoparticle-decorated template and subsequent stripping. PDMS endowed the resulting surface with excellent flexibility and stretchability. The use of nanoparticles contributed to the sustained roughening of the surface, even under large strain, offering mechanically durable superhydrophobicity. The resulting composite film could maintain its superhydrophobicity (water contact angle ≈ 161° and sliding angle close to 0°) under a large stretching strain of up to 100% and could withstand 500 stretching–releasing cycles without losing its superhydrophobic properties. Furthermore, the obtained film was resistant to long term exposure to different pH solutions and ultraviolet light irradiation, as well as to manual destruction, sandpaper abrasion, and weight pressing.

Stretchable superhydrophobic film was fabricated by casting silicone rubber polydimethylsiloxane (PDMS) on a SiO₂ nanoparticle-decorated template and subsequent stripping.

Selective Liquid Sliding Surfaces with Springtail-Inspired Concave Mushroom-Like Micropillar Arrays

Herein, a mushroom-like reentrant structure is proposed, inspired by springtails, to create a selective liquid sliding surface by implementing a simple yet sturdy silicon fabrication and lithography method. The fabricated arrays display high structural fidelity, presenting a novel geometry of a concave tip. The mushroom-like head shape of these structures is found to have superomniphobicity, which is independent of a variation of temperatures for even low surface tension liquids such as mineral oil. A design rule for the novel cap of the proposed structures, which results in a selective liquid sliding property with deionized (DI) water and mineral oil, is also investigated. It is demonstrated that oil starts to slide at a roll-off angle (ROA) 10° and then DI water rolls off at ROA 15° on the same fabricated transparent and flexible surface with repeatable durability.

Slippery Liquid-Attached Surface for Robust Biofouling Resistance

Materials for biodevices and bioimplants commonly suffer from unwanted but unavoidable biofouling problems due to the nonspecific adhesion of proteins, cells, or bacteria. Chemical coating or physical strategies for reducing biofouling have been pursued, yet highly robust antibiofouling surfaces that can persistently resist contamination in biological environments are still lacking. In this study, we developed a facile method to fabricate a highly robust slippery and antibiofouling surface by conjugating a liquid-like polymer layer to a substrate. This slippery liquid-attached (SLA) surface was created via a one-step equilibration reaction by tethering methoxy-terminated polydimethylsiloxane (PDMS-OCH₃) polymer brushes onto a substrate to form a transparent "liquid-like" layer. The SLA surface exhibited excellent sliding behaviors toward a wide range of liquids and small particles and antibiofouling properties against the long-term adhesion of small biomolecules, proteins, cells, and bacteria. Moreover, in contrast to superomniphobic surfaces and liquid-infused porous surfaces (SLIPS) requiring micro/nanostructures, the SLA layer could be obtained on smooth surfaces and maintain its biofouling resistance under abrasion with persistent stability. Our study offers a simple method to functionalize surfaces with robust slippery and antibiofouling properties, which is promising for potential applications including medical implants and biodevices.

Anisotropic Hexagonal Particles Induced by the Double-Solvent Swelling Method

Nonspherical anisotropic particles, as basic building blocks, have been catching much attention in recent decades. However, it is still a challenge to produce nonspherical particles by traditional approaches. Here, we reported a facile method to fabricate hexagonal particles via the double-solvent swelling method. When the crystal arrays were immersed in the double-solvent system of N,N-dimethylformamide (DMF) and tetraethyl orthosilicate (TEOS), the particles were swollen and squeezed into hexagonal particles. The concave size of hexagonal particles was controlled by tuning the mass ratio of the solvent and the swelling time. In addition, the particles with novel morphology were also prepared by swelling the arrays with a distinct lattice structure. The monodispersed particle possesses a well-defined hexagonal morphology and the liquid crystal phenomenon, which has promising applications in the fields of photonics, optical devices, and toners.

Superomniphobic Surfaces with Improved Mechanical Durability: Synergy of Hierarchical Texture and Mechanical Interlocking

Due to their unique functionality, superomniphobic surfaces that display extreme repellency toward virtually any liquid, have a wide range of potential applications. However, to date, the mechanical durability of superomniphobic surfaces remains a major obstacle that prevents their practical deployment. In this work, a two-layer design strategy was developed to fabricate superomniphobic surfaces with improved durability via synergistic effect of interconnected hierarchical porous texture and micro/nano-mechanical interlocking. The improved mechanical robustness of these surfaces was assessed through water shear test, ultrasonic washing test, blade scratching test, and Taber abrasion test.

Fabrication of a flexible transparent superomniphobic polydimethylsiloxane surface with a micropillar array

Although superomniphobic surfaces have attracted extensive interest owing to many important applications, successful fabrication of such surfaces still remains a critical challenge. Herein, we present a flexible transparent superomniphobic polydimethylsiloxane (PDMS) surface with a micropillar array using Si nanowires as the mould. The as-obtained PDMS not only exhibits excellent liquid-repellent performance with a static contact angle of over 150° and sliding angle of less than 6° against a wide range of liquids, but also maintains the super-repellency even under acid/base corrosion, mechanical damage, and unidirectional stretching.

Designing Transparent Micro/Nano Re-Entrant-Coordinated Superamphiphobic Surfaces with Ultralow Solid/Liquid Adhesion

Superamphiphobic surfaces, capable of repelling both water and oil, have been extensively studied recently. Artificial superamphiphobic surfaces with ultralow solid/liquid adhesion and high transparency have been achieved separately. However, simultaneous demonstration of these two features remains a challenge. Here, we designed a superamphiphobic surface possessing a re-entrant curvature on both nano- and microscales uniformly, each maintaining their capabilities. The achieved micro/nano re-entrant-coordinated superamphiphobic surface performed ultralow solid/liquid adhesion for liquids with high viscosities or low surface tension and showed excellent transparency. This rationally designed model of the superamphiphobic surface may provide useful guidelines for fabrication of superamphiphobic surfaces and enable potential applications ranging from self-cleaning materials to optical devices, such as solar panels, wind screens, and goggles.

Iridescence-controlled and flexibly tunable retroreflective structural color film for smart displays

Structural color materials, which use nano- or microstructures to reflect specific wavelengths of ambient white light, have drawn much attention owing to their wide applications ranging from optoelectronics, coatings, to energy-efficient reflective displays. Although various structural color materials based on specular or diffuse reflection have been demonstrated, neither efficient retroreflective structural colors nor iridescent and non-iridescent colors to different observers simultaneously were reported by existing artificial or natural structural color materials. Here, we show that by partially embedding a monolayer of polymer microspheres on the sticky side of a transparent tape, the spontaneously formed interferometric structure on the surface of air-cushioned microspheres can lead to unique structural colors that remain non-iridescent under coaxial illumination and viewing conditions, but appear iridescent under noncoaxial illumination and viewing conditions. Our findings demonstrate a smart, energy-efficient, and tunable retroreflective structural color material that is especially suitable for nighttime traffic safety and advertisement display applications.

Ultra-Thin Conductive Graphitic Carbon Nitride Assembly through van der Waals Epitaxy toward High-Energy-Density Flexible Supercapacitors

Graphitic carbon nitride is an ordered two-dimensional stability. However, its bulk structure with low electrical conductivity (less than 1 S cm^-1) restricts the applications in electrochemical energy storage. This is because conventional synthesis methods lack effective thickness control, and the excessive nitrogen doping (∼50%) leads to poor electrical conductivity. Here, we report an ultrathin conductive graphitic carbon nitride assembly (thickness of ∼1.0 nm) through graphene-templated van der Waals epitaxial strategy with high electrical conductivity (12.2 S cm^-1), narrow pore-size distribution (5.3 nm), large surface area (724.9 m² g^-1), and appropriate nitrogen doping level (18.29%). The ultra-thin structure with nitrogen doping provided numerous channels and active sites for effective ion transportation and storage, while the graphene layers acted as micro current collectors; subsequently, it exhibits high energy storage capability of 936 mF cm^-2 at 1 mA cm^-2 with excellent stability of over 10 000 cycles. Moreover, the all-solid-state supercapacitors showed an ultra-high energy density of 281.3 μWh cm^-2 at 1 mA cm^-2 with high rate capability, Coulombic efficiency, and flexibility. This work represents a general framework for the bottom-up synthesis of ultrathin 2D materials, which may promote the application of graphitic carbon nitride in energy storage.

Magnetic-Sensitive Nanoparticle Self-Assembled Superhydrophobic Biopolymer-Coated Slow-Release Fertilizer: Fabrication, Enhanced Performance, and Mechanism

Although commercialized slow-release fertilizers coated with petrochemical polymers have revolutionarily promoted agricultural production, more research should be devoted to developing superhydrophobic biopolymer coatings with superb slow-release ability from sustainable and ecofriendly biomaterials. To inform the development of the superhydrophobic biopolymer-coated slow-release fertilizers (SBSF), the slow-release mechanism of SBSF needs to be clarified. Here, the SBSF with superior slow-release performance, water tolerance, and good feasibility for large-scale production was self-assembly fabricated using a simple, solvent-free process. The superhydrophobic surfaces of SBSF with uniformly dispersed Fe₃O₄ superhydrophobic magnetic-sensitive nanoparticles (SMNs) were self-assembly constructed with the spontaneous migration of Fe₃O₄ SMNs toward the outermost surface of the liquid coating materials ( i.e., pig fat based polyol and polymethylene polyphenylene isocyanate in a mass ratio 1.2:1) in a magnetic field during the reaction-curing process. The results revealed that SBSF showed longer slow-release longevity (more than 100 days) than those of unmodified biopolymer-coated slow-release fertilizers and excellent durable properties under various external environment conditions. The governing slow-release mechanism of SBSF was clarified by directly observing the atmosphere cushion on the superhydrophobic biopolymer coating using the synchrotron radiation-based X-ray phase-contrast imaging technique. Liquid water only contacts the top of the bulges of the solid surface (10.9%), and air pockets are trapped underneath the liquid (89.1%). The atmosphere cushion allows the slow diffusion of water vapor into the internal urea core of SBSF, which can decrease the nutrient release and enhance the slow-release ability. This self-assembly synthesis of SBSF through the magnetic interaction provides a strategy to fabricate not only ecofriendly biobased slow-release fertilizers but also other superhydrophobic materials for various applications.

Biomimetic polymeric superamphiphobic surfaces: their fabrication and applications

In this review, we summarize recent developments in polymeric superamphiphobic surfaces, including their design, fabrication, and potential applications.