Robust Superhydrophobic Graphene-Based Composite Coatings with Self-Cleaning and Corrosion Barrier Properties

Preparation and properties of anti-weathering and superhydrophobic wood based on palm wax in polydimethylsilane nanocomposite coating

The superhydrophobic coating on wood surface is an effective method to improve the durability and service life of wood. In this paper, dodecyl modified gas-phase nano-SiO2 particles (M-SiO2), polydimethylsilane-trimethoxysilane ends (PDMS-Ts), palm wax, γ-glycidoxypropyl trimethoxysilane (KH560), and isopropyl titanate (TTIP) were blended and sprayed on the surface of wood by a simple one-step method at room temperature. The superhydrophobic modified wood has a water contact angle (WCA) of 161.2° and a sliding angle (SA) of less than 3°, demonstrating excellent anti-fouling, self-cleaning, and durability properties. Specifically, after undergoing various durability tests, including sandpaper abrasion (15 cycles), finger abrasion (30 cycles), sand impact (90 cycles), tape peeling (70 cycles), and chemical stability tests (24 h immersion in acidic and alkaline environments), the wood surface maintained its superhydrophobicity. Importantly, the wood's color remained virtually unchanged after superhydrophobic modification, preserving its inherent aesthetic properties. Moreover, after 768 h of artificial weathering, the color difference (ΔE*) of the modified wood was only 4.35, indicating excellent color stability, with the water contact angle remaining largely unchanged. Notably, the modified wood significantly delayed the combustion time and maintained its superhydrophobic properties after combustion tests. This study presents a novel method to achieve superhydrophobicity, weathering resistance, and flame retardancy in wood, offering new insights for the protection of wood used in outdoor applications.

Research on underwater air layer retention and antifouling ability of Salvinia-inspired biomimetic materials

Marine biofouling not only increases the navigation resistance of ships, accelerates the corrosion of metal substrates, but also hinders the healthy development of the marine economy. Inspired by the unique structure and function of Salvinia, we designed and fabricated biomimetic surfaces with superhydrophobic hairs and hydrophilic patches (SHHPs) using silicone rubber-graphene (SR-GN) and SR modified with polyacrylic acid (SR-PAA) composites. SHHPs can generate pinning effects underwater, forming an air layer as an environmentally friendly physical antifouling barrier. SHHPs exhibit strong capability in maintaining the air layer and can resist the attachment of bacteria and algae under static and simulated marine dynamic conditions. These results indicated that the physical antifouling strategy based on air layer provides a platform with broad application prospects for the maritime industry.

Anti-smudge superhard transparent coatings via ultra-small nanoparticle pattern surfaces

Anti-smudge coating materials have a broad prospect, but they are susceptible to wear from nails and sand. Therefore, the potential application of such coatings on glass substrates needs coating features such as superhardness and high transparency. However, realizing these key properties combined with anti-smudge function is significantly challenging. In this work, we show a conceptional nanoparticle pattern designing strategy of materials, inspired by stepping on cobblestone roads with the foot feeling of only the hardness of stones. Realize the nanoparticle pattern surface of "cobblestone roads" via facile and scalable interfacial reactions within a molecular compatible system, to successfully achieve the desired coating material properties including anti-smudge, superhardness, and high transparency. The coating was composed of tensely crosslinked sub-10 nm building blocks that bear an anti-smudge molecular layer, exhibiting undistinguished inorganic phase behavior when it was subjected to external forces within the contact point of micro- or above 10 nm nanoscale.

Graphene Mitigates Nanoscale Tribochemical Wear of Silica Glass in Water

Despite the ubiquitous use of glasses, their simultaneous susceptibility toward scratch-induced defects and atmospheric hydration deteriorates their mechanical and chemical durability. Here, it is demonstrated that the deposition of a few-layer graphene provides unprecedented wear resistance to silica glass in aqueous conditions. To this extent, nanoscale scratch tests are carried out on graphene-glass surfaces via contact-mode atomic force microscopy with chemically inert and reactive tips. It is observed that the graphene-glass exhibits up to ≈98% friction reduction and no discernable damage or material loss. This observation is in stark contrast to the behavior of bare silica glass which suffers severe tribochemical wear at equivalent contact conditions with even milder stresses. Further, through reactive molecular simulations, it is demonstrated that parallel mechanisms of lubrication and chemical passivity contribute to the enhanced damage resistance of graphene-glass surfaces against any countersurface chemistry. Altogether, the present study provides an impetus toward physically and chemically durable glass coatings exploiting the functionalities of two-dimensional materials.

Research Advances and Future Perspectives of Superhydrophobic Coatings in Sports Equipment Applications

In recent years, superhydrophobic coatings have attracted much attention due to their excellent water repellency and self-cleaning properties. They have broad application prospects in improving the performance and durability of sports equipment (such as clothing, footwear, balls, and protective equipment). Recent studies have shown that these coatings can improve water repellency, reduce friction, enhance traction, and extend the service life of sports equipment by preventing water absorption and reducing dirt accumulation. Despite their potential, the practical application of superhydrophobic coatings still faces many challenges, including difficulties in coating preparation, limited long-term durability, and high production costs that prevent large-scale production. This paper begins with an analysis of the current status of superhydrophobic coatings in sports equipment, from theory to application, from the basic Young's model to the novel Contact Line Pinning Model, analyzing the advantages and disadvantages of several methods in some aspects, focusing on the most commonly used preparation methods, including the template method, the gel-gel method, the deposition method, etc., and objectively analyzing the preparation methods to match the appropriate sports equipment applications. Despite these advances, there are still significant gaps in understanding the long-term performance of these coatings under real-world conditions. The paper concludes by identifying future research directions, with a focus on improving wear resistance, improving cost-effectiveness, and assessing the environmental impact of these materials. These insights will contribute to the continued development and application of superhydrophobic coatings in the field of sports equipment.

Wetting Transition from Wenzel to Cassie States: Thermodynamic Analysis

Superhydrophobicity is closely linked to the chemical composition and geometric characteristics of surface roughness. Building on our structural studies on water and air-water interfaces, this work aims to elucidate the mechanism underlying the wetting transition from the Wenzel to the Cassie state on a hydrophobic surface. In the Wenzel state, the grooves are filled with water, meaning that the surface roughness becomes embedded in the liquid. To evaluate the effects of surface roughness on water structure, a wetting parameter (WRoughness) is proposed, which is closely related to the geometric characteristics of roughness, such as pillar size, width, and height. During the wetting transition from Wenzel to Cassie states, the critical wetting parameter (WRoughness,c) may be expected, which corresponds to the critical pillar size (ac), width (wc), and height (hc). The Cassie state is expected when the WRoughness is less than WRoughness,c (ac), decreasing width (hc). Additionally, molecular dynamic (MD) simulations are conducted to demonstrate the effects of surface roughness on superhydrophobicity.

Triggering the Interplay of sp2-sp3 Carbon-Assisted Sustained Tribofilm via Two-Dimensional Surface Modulation for Exceptional Wear Resistance of Steel Surfaces

The relentless wear and friction of steel-based moving machinery have created ongoing challenges that hinder their industrial applications. One promising solution is the use of reduced graphene oxide (rGO) as a lubricant due to its excellent mechanical strength and promising tribological properties. However, its tendency to self-agglomerate presents a major hurdle for its practical use. This study aims to combat the restacking of rGO nanosheets by strategically intercalating self-assembled α-ZrP between the rGO layers, unlocking exceptional wear resistance in mild steel through hot-dip galvanization. The multilayer architecture of the developed coatings ensures lubrication through layer slippage during friction, while the coexistence of sp2-sp3 hybridized carbons further extends wear life, with the Zn-0.22/ZP_5@G coating exhibiting the highest wear resistance (0.277 × 10-7 mm3 N-1 m-1). The as-tailored composite coating, featuring a tribolayer composed of graphitic sp2 carbons, ZrO2, Zr(PO4)2, and Fe2O3, serves as an effective dissipative medium for contact stress. The formation of diamond-like sp3 carbons induced by the tribological process further contributes to the increased hardness of the resulting tribofilm. The reduced generation of the π-conjugated system in the composite prevents the movement of electrons toward the cathodic site, while the passivation effect induced by the composite effectively inhibits electrolyte permeation, resulting in substantial corrosion resistance. The exemplary wear resistance with remarkable anticorrosion performance achieved in this study offers significant improvement in the realm of hard coatings for mechanical applications, including moving machinery and manufacturing. Hence, the system can find effective use in such industries following the completion of relevant case studies.

Eco-Friendly Waterborne Polyurethane Coating Modified with Ethylenediamine-Functionalized Graphene Oxide for Enhanced Anticorrosion Performance

This study explores the potential of graphene oxide (GO) as an additive in waterborne polyurethane (WPU) resins to create eco-friendly coatings with enhanced anticorrosive properties. Traditionally, WPU's hydrophilic nature has limited its use in corrosion-resistant coatings. We investigate the impact of incorporating various GO concentrations (0.01, 0.1, and 1.3 wt%) and functionalizing GO with ethylenediamine (EDA) on the development of anticorrosive coatings for carbon steel. It was observed, by potentiodynamic polarization analysis in a 3.5% NaCl solution, that the low GO content in the WPU matrix significantly improved anticorrosion properties, with the 0.01 wt% GO-EDA formulation showing exceptional performance, high Ecorr (-117.82 mV), low icorr (3.70 × 10-9 A cm-2), and an inhibition corrosion efficiency (η) of 99.60%. Raman imaging mappings revealed that excessive GO content led to agglomeration, creating pathways for corrosive species. In UV/condensation tests, the 0.01 wt% GO-EDA coating exhibited the most promising results, with minimal corrosion products compared to pristine WPU. The large lateral dimensions of GO sheets and the cross-linking facilitated by EDA enhanced the interfacial properties and dispersion within the WPU matrix, resulting in superior barrier properties and anticorrosion performance. This advancement underscores the potential of GO-based coatings for environmentally friendly corrosion protection.

Superhydrophobic Solar-to-Thermal Materials Toward Cutting-Edge Applications

Solar-to-thermal conversion is a direct and effective way to absorb sunlight for heat via the rational design and control of photothermal materials. However, when exposed to water-existed conditions, the conventional solar-to-thermal performance may experience severe degradation owing to the high specific heat capacity of water. To tackle with the challenge, the water-repellent function is introduced to construct superhydrophobic solar-to-thermal materials (SSTMs) for achieving stable heating, and even, for creating new application possibilities under water droplets, sweat, seawater, and ice environments. An in-depth review of cutting-edge research of SSTMs is given, focusing on synergetic functions, typical construction methods, and cutting-edge potentials based on water medium. Moreover, the current challenges and future prospects based on SSTMs are also carefully discussed.

2D Nanomaterials Reinforced Organic Coatings for Marine Corrosion Protection: State of the Art, Challenges, and Future Prospectives

2D nanomaterials, with extraordinary physical and chemical characteristics, have long been regarded as promising nanofillers in organic coatings for marine corrosion protection. The past decade has witnessed the high-speed progress of 2D nanomaterial-reinforced organic composite coatings, and plenty of breakthroughs have been achieved as yet. This review covers an in-depth and all-around outline of the up-to-date advances in 2D nanomaterial-modified organic coatings employed for the marine corrosion protection realm. Starting from a brief introduction to 2D nanomaterials, the preparation strategies and properties are illustrated. Subsequently, diverse protection models based on composite coatings for marine corrosion protection are also introduced, including physical barrier, self-healing, as well as cathodic protection, respectively. Furthermore, computational simulations and critical factors on the corrosion protection properties of composite coatings are clarified in detail. Finally, the remaining challenges and prospects for marine corrosion protection based on 2D nanomaterials reinforced organic coatings are highlighted.

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

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

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.

Evaluation of Antibacterial, Antioxidant, Anti-inflammatory and Anticancer Efficacy of Titanium-Doped Graphene Oxide Nanoparticles

INTRODUCTION

The current development of nanoparticles (NPs) with significant antibacterial properties, low cost and low toxicity has made it possible to develop novel techniques for treatments in the medical field. The titanium metal oxide, when combined with a carbonaceous material like graphene, which has excellent absorbing capacity, is efficient in loading drugs and thus helps in drug delivery and also in biomedical applications like anticancer, anti-inflammatory, antioxidant, and antibacterial activities.

MATERIALS AND METHODS

Titanium-doped graphene oxide nanoparticles (Ti/GO-NPs) were processed by the one-pot synthesis method; further characterization was performed by using UV-visible spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), field emission electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX) analysis and biomedical applications like anticancer, anti-inflammatory, antioxidant and antibacterial activities.

RESULTS

The synthesized end product of Ti/GO-NPs showed a creamy white appearance. Subsequent characterization studies of UV-Vis spectroscopy revealed a peak level of 373 nm at 24 hours and 404 nm after 48 hours. FT-IR analysis exhibited a broad absorption band within the range of 1000-3500 cm-1, which was attributed to various chemical compounds of C-Br, C-I stretching, C=C bending, S=O stretching, O=H stretching, C=C stretching, H bonded and OH stretching to different absorbance wavelength ranges. SEM analysis exhibited quasi-spherical-shaped Ti/GO-NPs with an average particle size of 50- 100 nm and EDX analysis showed the elemental composition of 32.3% titanium 43.9% oxygen and 2.5% carbon. The antibacterial activity showed moderate activity against Staphylococcus aureus and no activity against Pseudomonas aeruginosa, Enterococcus faecalis and E. coli. The antioxidant activity exhibited 88% at 50 µg/mL concentration, the anti-inflammatory activity revealed 80% at 80 µg/mL concentration and the anticancer activity showed 21% at 150 µg/mL concentration.

CONCLUSION

The characterization and biomedical application conclude that a combination of Ti/GO-NPs will be efficient in drug delivery. The study showed moderate antibacterial activity and significant antioxidant, anti-inflammatory and anticancer activities. Considering their physiochemical properties, absorption capacity and mechanism of drug delivery, Ti/GO-NPs can be incorporated into various applications in the medical field.

Preparation of the graphene-based smart hydrophobic nanocomposite and its application in oil/water separation

Designing and synthesizing materials with smart hydrophobicity against an external magnetic field for efficient oil/water separation is of great importance due to the increasing problems caused by oil pollution. Here, the nanocomposites were fabricated based on graphene and different iron oxides exhibit smart hydrophobicity against an external magnetic field and they are in powder form eliminating the requirement for a substrate employing a facile and echo friendly method. The results prove that autoclaving of graphene leads to its ferromagnetic property; then it is attached to iron oxides by magnetic attraction and a nanocomposite is produced. The magnetic property of the resulting nanocomposite is higher than the magnetic property of its individual components. In addition, following nanocomposite formation, its hydrophobicity and surface area also change. FESEM images were taken from the nanocomposites to study their surface morphology, and EDS-MAP analysis to observe the elemental distribution uniformity of the nanocomposites. Also, to measure the surface area and pore size, BET analysis has been performed on pure materials and graphene-black iron oxide nanocomposite (graphene@black iron oxide). The results show that the specific surface area of black iron oxide increases after being composited with graphene dispersed at 5000 rpm. Indeed, graphene forms a composite by binding to iron oxide, and therefore, its specific surface area increases compared to iron oxide and graphene alone. These results show an increase in oil sorption and better separation of oil from water by the prepared nanocomposite. Also, to measure the magnetic properties of pure materials, graphene@black iron oxide, and ferromagnetic graphene at 3000 and 5000 rpm, the Vibrating Sample Magnetometer analysis has been performed. The results have proven that the nanocomposite powder prepared by a simple method obtained from cost-effective and available materials is hydrophobic and becomes more hydrophobic by applying an external magnetic field. Due to the ease with which oil can be readily removed from the nanocomposite by eliminating the external magnetic field, this nanocomposite is an excellent choice for the separation of oil from water.

Hydrophobicity and Improved Corrosion Resistance of Weathering Steel via a Facile Sol-Gel Process with a Natural Rust Film

Weathering steel, which has a protective corrosion product film, is widely used in various construction and landscaping applications. However, it causes metal contamination in the receiving ecosystem via corrosion-induced metal dissolution and rust runoff. Traditional corrosion prevention methods, such as surface coating, also suffer from environmental pollution and high maintenance costs. In this study, we propose a novel method to make the rust film hydrophobic to prevent corrosion while retaining its original appearance. The crystalline rust is used as a natural skeleton, and nano-SiO2 particles are synthesized in situ on it by a facile sol-gel method. The microscopic analysis shows that the flower-like rust flakes provide a primary structure (micrometric scales) and the nano-SiO2 particles form a secondary structure (nanoscale bumps), which is the essential micronanostructure for forming a hydrophobic surface. The as-synthesized film shows strong corrosion resistance, with the corrosion current density being 4 orders of magnitude lower than that of the samples without hydrophobicity. The hydrophobic surface not only prevents corrosive substances from penetrating into the rust layer but also reduces the risk of contamination through its self-cleaning properties. Therefore, the weathering steel with a hydrophobic rust film can be more stable and environmentally friendly for multiscenario applications.

Effect of the Addition of Graphene Flakes on the Physical and Biological Properties of Composite Paints

In this study, graphene flakes were obtained using an electrolytic method and characterized using X-ray diffraction (XRD), Raman and FTIR spectroscopy, scanning and transmission electron microscopy (SEM/TEM). Graphene-based composites with varying concentrations of 0.5%, 1% and 3% by weight were prepared with acrylic paint, enamel and varnish matrices. The mechanical properties were evaluated using micro-hardness testing, while wettability and antimicrobial activity against three pathogens (Staphylococcus aureus 33591, Pseudomonas aeruginosa 15442, Candida albicans 10231) were also examined. The results indicate that the addition of graphene flakes significantly enhances both the mechanical and antimicrobial properties of the coatings.

Anticorrosion, Thermal Degradation, and Hydrophobic Performances of Graphene/TiO2 Nanocomposite Coatings

Globally, researchers have devoted consistent efforts to producing excellent coating properties since coating plays an essential role in enhancing electrochemical performance and surface quality. In this study, TiO₂ nanoparticles in varying concentrations of 0.5, 1, 2, and 3 wt.% were added into the acrylic-epoxy polymeric matrix with 90:10 wt.% (90A:10E) ratio incorporated with 1 wt.% graphene, to fabricate graphene/TiO2 -based nanocomposite coating systems. Furthermore, the properties of the graphene/TiO2 composites were investigated by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), ultraviolet-visible (UV-Vis) spectroscopy, water contact angle (WCA) measurements, and cross-hatch test (CHT), respectively. Moreover, the field emission scanning electron microscope (FESEM) and the electrochemical impedance spectroscopy (EIS) tests were conducted to investigate the dispersibility and anticorrosion mechanism of the coatings. The EIS was observed by determining the breakpoint frequencies over a period of 90 days. The results revealed that the TiO2 nanoparticles were successfully decorated on the graphene surface by chemical bonds, which resulted in the graphene/TiO2 nanocomposite coatings exhibiting better dispersibility within the polymeric matrix. The WCA of the graphene/TiO2 coating increased along with the ratio of TiO2 to graphene, achieving the highest CA of 120.85° for 3 wt.% of TiO₂. Excellent dispersion and uniform distribution of the TiO2 nanoparticles within the polymer matrix were shown up to 2 wt.% of TiO₂ inclusion. Among the coating systems, throughout the immersion time, the graphene/TiO2 (1:1) coating system exhibited the best dispersibility and high impedance modulus values (Z0.01 Hz), exceeding 1010 Ω cm2.

Blood compatible and noncytotoxic superhydrophobic graphene/titanium dioxide coating with antibacterial and antibiofilm properties

The potential of superhydrophobic surfaces has gained vast attention in medical settings due to their self‐cleaning effect (including bacterial colonization reduction), minimized cell‐to‐surface interaction, and anti‐biofouling effect. These valuable features allow the vanquishment of some limitations accompanying the blood‐contacting medical devices that are widely used in clinical practice. The extracorporeal circulation used to perform hemodialysis, for instance, as well as the blood collection sets, these essential blood‐contacting medical devices are frequently associated with bacterial infection and hemolysis. Within this study, superhydrophobic surface was substantiated to enhance the biocompatibility. Herein, the graphene (Gr) and titanium dioxide (TiO2) nanoparticles were dip‐coated on poly(lactic acid) (PLA) film to produce a superhydrophobic surface. The uniform distribution of the Gr/TiO2 nanoparticles of the coating enhanced the surface roughness and therefore promoted superhydrophobic properties. Co‐occurrence of the Cassie‐Baxter regime and Wenzel regime was suggested to induce the low surface wettability. The superhydrophobic Gr/TiO2 demonstrated significant inhibition of biofilm formation and antibacterial activity against Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa. Besides, the in vitro blood compatibility assay showed a hemolysis rate lower than 2%, which was categorized as nonhemolytic. The exposure of human heart cells and kidney cells to the Gr/TiO2‐coated PLA film did not significantly affect the cell viability. The findings herein showed promising results for the superhydrophobic Gr/TiO2‐coated PLA film to act as a potential biomaterial for single‐use blood‐contacting medical devices. This study also provided insight for future medical applications that require superhydrophobic coatings.

Bio-Based Porous Aerogel with Bionic Structure and Hydrophobic Polymer Coating for Efficient Absorption of Oil/Organic Liquids

Increasing contamination risk from oil/organic liquid leakage creates strong demand for the development of absorbents with excellent hydrophobicity and absorption capacity. Herein, bagasse was carbonized to form porous char with a special structure of array-style and vertically perforated channels, and then the activation process enlarged the pore volume of the char. With the cooperation of low-surface-energy polydimethylsiloxane and diatomaceous earth particles, the modified activated carbon aerogel (MACA) was fabricated by modifying the surface coating and mastoid structure on the bagasse char. Moreover, the MACA demonstrates high porosity oil-water separation, hydrophobicity, and considerable absorption capacity (4.06–12.31 g/g) for gasoline and various organic solvents. This work converts agricultural waste into an efficient porous adsorbent, offering a scalable and commercially feasible solution to solving the leakages of oil/organic solvents.

Superhydrophilic–superhydrophobic patterned surfaces: From simplified fabrication to emerging applications

Superhydrophilic–superhydrophobic patterned surfaces constitute a branch of surface chemistry involving the two extreme states of superhydrophilicity and superhydrophobicity combined on the same surface in precise patterns. Such surfaces have many advantages, including controllable wettability, enrichment ability, accessibility, and the ability to manipulate and pattern water droplets, and they offer new functionalities and possibilities for a wide variety of emerging applications, such as microarrays, biomedical assays, microfluidics, and environmental protection. This review presents the basic theory, simplified fabrication, and emerging applications of superhydrophilic–superhydrophobic patterned surfaces. First, the fundamental theories of wettability that explain the spreading of a droplet on a solid surface are described. Then, the fabrication methods for preparing superhydrophilic–superhydrophobic patterned surfaces are introduced, and the emerging applications of such surfaces that are currently being explored are highlighted. Finally, the remaining challenges of constructing such surfaces and future applications that would benefit from their use are discussed.

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.

Ultrasensitive and Recyclable Multifunctional Superhydrophobic Sensor Membrane for Underwater Applications, Weather Monitoring, and Wastewater Treatment

Although flexible sensors have attracted considerable attention in emerging fields, including wearable electronics and soft robotics, their stability must be considered in practical applications, especially the effects of external factors on the sensing performance. Herein, a recyclable flexible sensor with superhydrophobicity and a highly sensitive strain response was developed by combining electrospinning and ultrasonication anchoring techniques. The constructed hierarchical network structure is composed of the fluorine-free superhydrophobic multiwalled carbon nanotubes and a porous elastomer membrane substrate reinforced by nanoparticles. The obtained sensor exhibited exceptional strain-sensing performance in terms of ultrahigh sensitivity (maximum gauge factor of 12 172.46), a fast response time of 80 ms, and excellent durability (10 000 cycles). Based on these outstanding merits, the strain sensor can detect various human motions without being interfered with by harsh environments. Moreover, superhydrophobic membranes can be combined with electronic devices for weather monitoring and underwater sensing. Noteworthily, damaged sensors can be quickly dissolved by a small amount of cyclohexane, enabling material recovery. The recyclable multifunctional membranes could reduce the potential pollution to the environment and show highly promising applications in complex environments.

Superhydrophobic nanohybrid sponges for separation of oil/ water mixtures

The industrial revolution has led to different types of environmental pollution, including frequent leakage of crude oil to marine waters and the contamination of wastewater with immiscible or emulsified oils and organic liquids from various industrial residues. Hence, developing multifunctional materials for oil/water separation is a field of high significance for the remediation of oil-polluted water. Recently, advanced superwetting materials have been employed for oily wastewater treatment. This review summarizes the recent development in fabricating superhydrophobic/superoleophilic nanohybrid polyurethane, melamine, and cellulose sponges for oil/water separation. The use of organic and/or inorganic nanohybrid materials opens the horizon for designing a diverse and wide range of superhydrophobic sponges due to the synergistic effect between the surface roughness and chemical composition. The discussion is organized based on different classes of low surface energy materials including thermoplastics, thermosets, elastomers, fluorinated polymers, conductive polymers, organosilanes, long alkyl chain compounds, and hydrophobic carbon-based materials. Recent examples for the separation of both immiscible and emulsified oil/water mixtures are presented, with a focus on fabrication strategies, separation efficiency, recyclability, mechanical performance, and durability. Currently, most studies did not focus on the mechanical/chemical stability of the fabricated sponges, and hence, future research directions shall address the fabrication of robust and long-term durable superhydrophobic sponges with proper guidelines. Similarly, more research focus is required to design superhydrophobic sponges for the separation of emulsified oil/water mixtures and heavy crude oil samples. Superhydrophobic sponges can be employed for treatment of oily wastewater, emulsion separation, and cleanup of crude oil spills.

Superhydrophobic Ni-Reduced Graphene Oxide Hybrid Coatings with Quasi-Periodic Spike Structures

Recently, sophisticated technologies are applied to design a certain surface nature that can have superhydrophobic properties. Thus, a simple spray technique was introduced to prepare a superhydrophobic surface using rGO with Ni-S system (rGO-Ni) by using NiSO4 catalyst under microwave irradiation at various reaction times of 5, 10, 20, and 30 min. The GO reduction was conducted at a fixed Ar/H2 ratio, a flow rate of 0.4 L/min, microwave power of 720 W, and a mass of 0.5 g. GO powder with nickel sulfate catalyst was treated under Ar/H2 (4:1) mixture for GO reduction, where Ar and H2 were expected to prevent the rebinding of oxygen released from GO. The result of XRD and Raman measurement confirms that rGO-Ni prepared at reaction time 20 min exhibit the highest reduction of GO and the presence of various Ni-S crystal structures such as NiS, NiS2, Ni3S2, and Ni3S4 due to decomposition of NiSO4. The rGO-Ni coating performance shows superhydrophobic nature with a contact angle of 150.1°. The AFM images show that the addition of nickel to rGO produces a quasi-periodic spike structure, which increases the superhydrophobicity of the r-GO-Ni coated glass with a contact angle of 152.6°. It is emphasized that the proposed simple spray coating using rGO-Ni provides a more favorable option for industry application in obtaining superhydrophobic surfaces.

Fabrication and Characterization of Superhydrophobic Graphene/Titanium Dioxide Nanoparticles Composite

Materials with superhydrophobic surfaces have received vast attention in various industries due to their valuable properties, such as their self-cleaning and antifouling effects. These promising superhydrophobic properties are taken into high priority, particularly for medical devices and applications. The development of an ideal superhydrophobic surface is a challenging task and is constantly progressing. Various strategies have been introduced; however, a minority of them are cost-effective. This work presents a facile fabrication of the superhydrophobic surface by using graphene and titanium dioxide (TiO₂) nanoparticles. The graphene and TiO₂ hybrid nanoparticles are dip-coated on a biodegradable thermoplastic poly(lactic acid) (PLA) substrate. The thermoplastic PLA is approved by the Food and Drug Administration (FDA), and is widely utilized in medical devices. The graphene/TiO₂ coating is substantiated to transform the hydrophilic PLA film into superhydrophobic biomaterials that can help to reduce hazardous medical-device complications. The surface wettability of the graphene/TiO₂ nanoparticle-coated PLA surface was evaluated by measuring the apparent water contact angle. The surface chemical composition and surface morphology were analyzed via Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The graphene/TiO₂-coated PLA film achieved superhydrophobic properties by demonstrating a water contact angle greater than 150°. The water contact angle of the graphene/TiO₂ coating increased along with the concentration of the nanoparticles and the ratio of TiO₂ to graphene. Moreover, the graphene/TiO₂ coating exhibited excellent durability, whereby the contact angle of the coated surface remained unchanged after water immersion for 24 h. The duration of the effectiveness of the superhydrophobic coating suggests its suitability for medical devices, for which a short duration of administration is involved. This study reports an easy-to-replicate and cost-effective method for fabricating superhydrophobic graphene/TiO₂-coated surfaces, which additionally substantiates a potential solution for the manufacturing of biomaterials in the future.

Preparation and characterization of super hydrophobic aerogels derived from tunicate cellulose nanocrystals

First time aerogels composite with super hydrophobic properties were developed by using tunicate cellulose nanocrystals (TCNC), which expanded the application scope of animal cellulose resources. In this study, the TCNC was firstly cross-linked with silica and methyltrimethylsilane (MTMS), further coated with fluorodopa to form an aerogel with super hydrophobic properties. The aerogel was characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectroscopy (XPS). Results indicated that the contact angle of aerogel was 158.7°, which showed good hydrophobicity. The composite aerogel has superior stability in wide pH range, after 72 h immersion in pH = 0 and 12 solutions, the contact angle was still greater than 150°. The aerogel shows excellent oil-water separation ability and it can be repeatedly used more than 10 times. The separation efficiency can all reach more than 90% for different water-oil mixtures. This synthesized super hydrophobic aerogels derived from tunicate cellulose has greatly extended the application of marine animal celluloses.

Preparation and Self-Cleaning Performance of Carbon-Based Superhydrophobic Coatings Based on Non-Fluorine and Non-Toxic Corn Straw

Recently, superhydrophobic surfaces with self-cleaning ability have attracted broad research interest due to their huge potential in daily lives and industrial applications, but the use of fluorinate, toxic organic compounds, and expensive feedstocks make superhydrophobic materials a great challenge in practical application. In this study, we present a facile dip-coating strategy to prepare superhydrophobic coatings with self-cleaning properties based on a non-fluorine and non-toxic system by using eco-friendly corn straw as raw material. During this process, aromatic carbon particles with rough hierarchical structures were prepared firstly via a simple fast pyrolysis process, followed by modification with polydimethylsiloxane (PDMS) in absolute ethanol solvent to decrease the surface free energy. Research shows these natural straw-derived carbons display a microstructure of several protrusions which is similar to the lotus leave’s and the resulted coatings exhibit an outstanding superhydrophobic property with a static water contact angle (WCA) of 151.67 ± 1.36 degrees. In addition, the as-prepared coatings possessed excellent self-cleaning performance: no contaminations were observed on the surfaces after examining with sludge, calcimine, water, and common liquids such as tea, milk, soybean milk as well as ink, which have a broad range of potential application in the field of antifouling, waterproofing, and anticorrosive.

Photoredox Catalysis for the Fabrication of Water-Repellent Surfaces with Application for Oil/Water Separation

Silanization processes with perfluoroalkyl silanes have been demonstrated to be effective in developing advanced materials with many functional properties, including hydrophobicity, water repellency, and self-cleaning properties. However, practical industrial applications of perfluoroalkyl silanes are limited by their extremely high cost. On the basis of our recent work on photoredox catalysis for amidation with perfluoroalkyl iodides, its application for surface chemical modification on filter paper, as an illustrative example, has been developed and evaluated. Before photocatalytic amidation, the surface is functionalized with amine functional groups by silanization with 3-(trimethoxysilyl)propylamine. All chemically modified surfaces have been fully characterized by attenuated total reflection infrared (ATR-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and three-dimensional (3D) profiling to confirm the successful silanization and photocatalytic amidation. After surface modification of the filter papers with perfluoroalkanamide, they show high water repellency and hydrophobicity with contact angles over 120°. These filter papers possess high wetting selectivity, which can be used to effectively separate the organic and aqueous biphasic mixtures. The perfluoroalkanamide-modified filter papers can be used for separating organic/aqueous biphasic mixtures over many cycles without lowering the separating efficiency, indicating their reusability and excellent durability.

Comparative antibacterial activity of 2D materials coated on porous-titania

Plasma electrolytic oxidation (PEO) is a well-established technique for the treatment of titanium-based materials. The formed titania-PEO surface can improve the osseointegration properties of titanium implants. Nevertheless, it can not address bacterial infection problems associated with bone implants. Recently, 2-dimensional (2D) materials such as graphene oxide (GO), MXene, and hexagonal boron nitride (hBN) have received considerable attention for surface modifications showing their antibacterial properties. In this paper, a comparative study on the effect of partial deposition of these three materials over PEO titania substrates on the antibacterial efficiency and bioactivity is presented. Their partial deposition through drop-casting instead of continuous film coating is propsed to simultaneously address both antibacterial and osseointegration abilities. Our results demonstrate the dose-dependent nature of the deposited antibacterial agent on the PEO substrate. GO-PEO and MXene-PEO samples showed the highest antibacterial activity with 70 (±2) % and 97 (±0.5) % inactivation of S. aureus colonies in the low concentration group, respectively. Furthermore, only samples in the higher concentration group were effective against E. coli bacteria with 18 (±2) % and 17 (±4) % decrease in numbers of colonies for hBN-PEO and GO-PEO samples, respectively. Moreover, all antibacterial samples demonstrated acceptable bioactivity and good biocompatibility, making them a considerable candidates for the next generation of antibacterial titanium implants.

Review on the recent development of durable superhydrophobic materials for practical applications

Biomimetic superhydrophobic surfaces show great potential in oil-water separation, anti-icing and self-cleaning. However, due to the instability caused by its fragile structure and non-durable superhydrophobicity, it is difficult to apply them in the actual field. Here, by introducing surface wettability and analysing the mechanism of superhydrophobic failure, it is concluded that the reason for the failure of the superhydrophobic surface comes from the transition of the surface energy and the hysteresis of the contact angle (CA). On the basis of this analysis, it is concluded that the principle of designing a durable superhydrophobic surface is to satisfy one of the following three points: improving the binding force between molecules, introducing durable materials and improving chemical durability. On this basis, a variety of preparation methods are proposed, such as assembly method and spray/dip coating method, and the design and preparation of a self-healing surface inspired by nature will also be included in the introduction. Last but not least, the preparation and application of a durable super-hydrophobic surface in oil-water separation, anti-icing and self-cleaning are also introduced in detail. This review reveals the conclusions and prospects of durable superhydrophobic surfaces, and aims to inspire more researchers to invest in this research.

A Hydrophobic Sisal Cellulose Microcrystal Film for Fire Alarm Sensors

At present, environmentally friendly biobased flexible films are of particular interest as next-generation fireproof packaging and sensor materials. To reduce the moisture uptake and fire risks induced by hygroscopic and flammable biobased films, we report a simple and green approach to develop a hydrophobic, flame-retardant composite film with synergetic benefit from soy protein isolate (SPI), sisal cellulose microcrystals (MSF-g-COOH), graphene nanosheets (GN), and citric acid (CA). Compared with SPI/MSF-g-COOH composite films, the as-prepared SPI/MSF-g-COOH/CA/GN composite films have significantly improved water resistance and can maintain excellent physical structure and good electrical conductivity in an ethanol flame. This work opens a pathway for the development of novel fire-retardant fire alarm biosensors.

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.

Porosity-induced mechanically robust superhydrophobicity by the sintering and silanization of hydrophilic porous diatomaceous earth

HYPOTHESIS

Because they have self-similar low-surface-energy microstructures throughout the whole material block, fabricating superhydrophobic monoliths has been currently a promising remedy for the mechanical robustness of non-wetting properties. Noticeably, porous materials have microstructured interfaces throughout the complete volume, and silanization can make surfaces low-surface-energy. Therefore, the porous structure and surface silane-treatment can be combined to render hydrophilic inorganics into mechanically durable superhydrophobic monoliths.

EXPERIMENTS

Superhydrophobic diatomaceous earth pellets were produced by thermal-sintering, followed by a silanization process with octyltriethoxysilane. The durability of superhydrophobicity was evaluated by changes in wetting properties, surface morphology, and chemistry after a systematic abrasion sliding test.

FINDINGS

The intrinsic porosity of diatomite facilitated surface silanization throughout the whole sintered pellet, thus producing the water-repelling monolith. The abrasion sliding converted multimodal porosity of the volume to hierarchical roughness of the surface comprised of silanized particles, thereby attaining superhydrophobic properties of high contact angles over 150° and sliding angles below 20°. The tribological properties revealed useful information about the superhydrophobicity duration of the non-wetting monolith against friction. The result enables the application of porous structures in the fabrication of the anti-abrasion superhydrophobic materials even though they are originally hydrophilic.

Solvent-Free Fabrication of Robust Superhydrophobic Powder Coatings

Superhydrophobicity originating from the "lotus effect" enables novel applications such as self-cleaning, anti-fouling, anti-icing, anti-corrosion, and oil-water separation. However, their real-world applications are hindered by some main shortcomings, especially the organic solvent problem, complex chemical modification of nanoparticles, and poor mechanical stability of obtained surfaces. Here, we report for the first time the solvent-free, chemical modification-free, and mechanically, chemically, and UV robust superhydrophobic powder coatings. The coatings were fabricated by adding commercially available polytetrafluoroethylene (PTFE) particles into powder coatings and by following the regular powder-coating processing route. The formation of such superhydrophobic surfaces was attributed to PTFE particles, which hindered the microscale leveling of powder coatings during curing. Through adjusting the dosage of PTFE, the hydrophobicity of obtained coatings can be tuned in a large range (water contact angle from 92 to 162°). The superhydrophobic coatings exhibited remarkable mechanical robustness against abrasion because of the unique hierarchical micro/nanoscale roughness and low surface energy throughout the coating and the solid lubrication effect of PTFE particles. The coatings also have robustness against chemical corrosion and UV irradiation owing to high bonding energy and chemical inertness of PTFE. Moreover, the coatings show attractive performances including self-cleaning, anti-rain, anti-snow, and anti-icing. With these multifaceted features, such superhydrophobic coatings are promising for outdoor applications. This study also contributes to the preparation of robust superhydrophobic surfaces in an environmentally friendly way.

A Cost-Effective Method for Preparing Robust and Conductive Superhydrophobic Coatings Based on Asphalt

The wide application of superhydrophobic materials is mainly hindered by the poor mechanical robustness and complicated preparation method. To overcome these problems, we tried to make a combination of hierarchical and self-similar structure by the means of a simple spraying method. By adding nanofiller (carbon nanotube) and microfiller (graphite powder and expanded graphite), the hierarchical structure was constructed. By further doping the fillers in the commercial asphalt uniformly, the self-similar structure was prepared. Based on the aforementioned work, the as-prepared sample could withstand the sandpaper abrasion for 12.00 m under 4.90 kPa. Moreover, this superhydrophobic coating demonstrated good conductivity, superior self-cleaning property, and excellent corrosion resistance. The integration of conductivity with the superhydrophobicity might open new avenues for ground grid applications.

Superhydrophobic graphene-based materials with self-cleaning and anticorrosion performance: An appraisal of neoteric advancement and future perspectives

Lotus like materials having superhydrophobicity is attaining greater demand due to the possibility of molding them into different high end applications. The major issue related to self-cleaning superhydrophobic surfaces is their restricted mechanical properties. The development of nanotechnology has brought many advantages in the fabrication and properties of superhydrophobic surfaces and thus it enhanced the demand of superhydrophobic surfaces. Many scientific groups have studied and reported about the superhydrophobicity exhibited by graphene and its analogous derivatives. The fabrication of the devices having properties ranging from anti-sticking and self-cleaning to anti-corrosion and low friction is made possible by the incorporation of this wonderful two-dimensional material. This review focuses on the preparation and properties of graphene based superhydrophobic coating materials with special mention to the wide range of applications rendered by them.

A case of oral foreign-body granuloma due to diatoms

Diatoms are photosynthetic algae with a siliceous exoskeleton. Diatoms are utilized by a wide array of industries for applications such as filtration and pest control. Unsubstantiated claims have also propelled their societal reach to trendy oral and topical uses. This case highlights a rare case of an oral granuloma secondary to diatoms. An 80-year-old woman presented with a mobile, firm, asymptomatic submucosal mass on her lower left mandibular vestibular mucosa. Histopathology showed a non-caseating granulomatous reaction to diatoms. Her only verified contact with a diatomaceous earth product was a dental impression using alginate after upper front teeth trauma 5 months before. Although there have been several cases of allergic contact dermatitis attributed to diatoms, there are no reported cases of diatom-induced granuloma formation found in the literature. There are, however, ample data on granulomas initiated by silica. Given the silica-based composition of diatoms, and the broad use of diatoms in industry and alternative medicine, it is unclear why diatom-induced granulomas are not more widely described. This report may alert clinicians to the existence of diatom granulomas and incline them to tailor their history to cover questions about possible exposure when evaluating patients presenting with a localized oral lesion.

Superhydrophobic Antireflection Coating on Glass Using Grass-like Alumina and Fluoropolymer

This work presents a superhydrophobic antireflective (AR) coating on glass. The coating consists of a grass-like alumina layer capped with plasma-deposited fluoropolymer. The grass-like alumina is formed by hot water treatment of atomic layer-deposited alumina on glass, and the fluoropolymer is plasma-deposited from CHF₃. Excellent broadband AR performance is observed in the visible spectrum with an average transmission of 94.9% for single-sided coated glass, which is close to the maximum 95.3% possible for this glass. Extremely desirable contact angles are obtained with 5-7 min-long fluoropolymer treatments on grass-like alumina with 173° advancing and 160° receding contact angles. This type of multifunctional coating can be beneficial in a multitude of applications like self-cleaning AR coating for solar panels, windows in high-rise buildings, sensors, and aerospace applications as well as just utilizing the excellent water repellent behavior in applications where only superhydrophobicity is required.