Rough Structure of Electrodeposition as a Template for an Ultrarobust Self-Cleaning Surface

Study on the Pyrolysis and Fire Extinguishing Performance of High-Temperature-Resistant Ultrafine Dry Powder Fire Extinguishing Agents for Aviation Applications

Ultrafine KAl(OH)2CO3 dry powder (UDWP), as a novel high-temperature-resistant ultrafine dry powder fire extinguishing agent, has garnered significant attention in the field of aviation fire protection. However, its development has been hindered by its hydrophilicity, which leads to hygroscopicity, and its tendency for re-ignition due to oil deposition. Therefore, this study employs perfluorodecyltrimethoxysilane (PFDTMS) to modify the surface of UDWP, resulting in hydrophobic and oleophobic M-UDWP. The thermal stability and hydrophobicity of M-UDWP ensure its long-term stable storage in aircraft equipment compartments, thereby reducing aircraft maintenance costs. Additionally, its oleophobicity provides excellent anti-re-ignition performance, protecting aircraft power compartments from secondary fire damage. Energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses indicate that the PFDTMS modifier was successfully grafted onto KAl(OH)2CO3. Furthermore, M-UDWP exhibits a three-stage thermal decomposition process. The first-stage decomposition can be regarded as a single-step reaction, and the calculated kinetic parameters provide accurate predictions. Thermogravimetric analysis-Fourier transform infrared spectroscopy-mass spectrometry (TG-FTIR-MS) results reveal that M-UDWP significantly produces H2O and CO2 during thermal decomposition, which is one of its core fire extinguishing mechanisms. For the combustion of #RP-3 and #RP-5 aviation kerosene, commonly found in aircraft engine nacelles, the extinguishing times required by M-UDWP are 243 ms and 224 ms, respectively, with minimum extinguishing concentrations (MEC) of 25.9 g/m3 and 23.4 g/m3, respectively. The study of M-UDWP's thermal stability aids in understanding its storage stability under high-temperature conditions and its fire extinguishing mechanisms in fire zones. Moreover, the research findings suggest that M-UDWP has the potential to replace Halon 1301 in aircraft engine nacelles.

Chemical Etching, Thermally Driven Combination Strategy to Fabricate Superhydrophobic Fe-Based Amorphous Coatings with Excellent Anticorrosion Property: Based on Hydroxylation Effect

Fe-based amorphous coatings are ideal materials for surface protection due to their outstanding mechanical properties and corrosion resistance. However, coating defects are inevitably formed during the preparation of coatings by thermal spray technology, which seriously affects the corrosion performance. Inspired by bionics, conceiving superhydrophobic surfaces with liquid barrier properties has become a new idea for the corrosion protection of metal surfaces. In this work, based on surface hydroxylation, we designed a superhydrophobic Fe-based amorphous coating with corrosion resistance by chemical etching combined with a thermally driven preparation strategy. The obtained superhydrophobic coatings exhibit liquid repellency (contact angle >150°) and excellent corrosion resistance (corrosion current density and passive current density reduced by 3 orders of magnitude). The results revealed that the superhydrophobic behavior stems from the construction of hydroxyl-induced surface micro-/nanomultilevel aggregates (cluster structures). The hydrophobic agent layer deposited on the surface of cluster aggregates and the nanoparticle elements that constitute the clusters dominate the corrosion resistance of the coating. This work provides an effective guide to the design of high-corrosion-resistant Fe-based amorphous alloy coatings and promotes their engineering applications.

Recovery of Al2O3 from hazardous Al waste as a reinforcement particle for high-performance Ni/Al2O3 corrosion resistance coating via ultrasonic-aided supercritical-CO2 electrodeposition

The unprocessed dumping of aluminium wastes in the landscape leads to generation of heat and toxic gases, which are detrimental to the ecosystem. Motivated by the waste-to-wealth notion, we demonstrated the recovery of aluminium oxide nanoparticles (Al₂O₃NPs) from domestic aluminium wastes via a sonochemical approach and synthesis of nickel/aluminium oxide (Ni/Al₂O₃) coating via ultrasonic-coupled supercritical carbon dioxide (US-SC-CO₂) electrodeposition method for higher corrosion resistance performance. The physical characterization and material confirmation of prepared films were examined by microscopic and various spectroscopic techniques. The electrochemical corrosion resistance studies were explored via potentiodynamic polarization and electrochemical impedance spectroscopy techniques. Based on the results, the US-SC-CO₂ strategy exposed an improved distribution of Al₂O₃ NPs assimilation in Ni matrix, higher corrosion resistance, and microhardness. The integration of ultrasonic irradiation into the SC-CO₂ process promises an enhanced coating quality. Thereby, the novel US-SC-CO₂ approach for Ni/Al₂O₃ synthesis is expected to achieve a sustainable green impact in real-world applications.

Functional Microtextured Superhydrophobic Surface with Excellent Anti-Wear Resistance and Friction Reduction Properties

The wear-resistant superhydrophobic (SHB) surfaces with excellent water-repellency ability were prepared by constructing a microtextured armor on an aluminum surface. With the assistance of laser-induced microtextures, the SHB surface could keep a longer water-repellency ability and a lower friction coefficient even after repeated friction tests under different loads and at different speeds. The mechanism of microtexture-protecting SHB coating is revealed based on both theoretical and elemental analysis. Additionally, we explore the relationship between the three-dimensional topography parameters (ISO 25178) and variation of water contact angles under different test recycles. The results show that the rough surface with appropriate S_a and higher S_ku exhibits a better wear resistance, which is mainly related to the storing ability of SHB coating inside the microtextures. Moreover, the surface with appropriate S_tr exhibits excellent wear resistance, which is mainly associated with better chip-removal ability. Finally, the tribological properties of the microtextured SHB surface are researched. It is worth noting that compared with the microtextured surface without SHB coating and the SHB-coated surface without microtextures, the microtextured SHB surface has the lowest friction coefficient under dry friction because the SHB coating would largely decrease the surface energy of the interface, so the adhesion friction decreases. The microtexture armor on the surfaces would protect the wear of SHB coating, so the SHB coating inside the microtexture could continuously play the role of a particle lubricant at the sliding interface and decrease the friction force of the sliding interface. We believe that the present study would contribute to the further understanding of the constructing mechanism of anti-wear SHB surfaces and provide a new strategy for topography design of engineering surfaces with friction reduction properties.

A General Strategy towards Superhydrophobic Self-Cleaning and Anti-Corrosion Metallic Surfaces: An Example with Aluminum Alloy

Corrosion and contamination of metallic structures can cause loss of their functionality as well as aesthetic values. In this study, we describe a general strategy to prepare superhydrophobic self-cleaning and anti-corrosion surfaces for metallic structures. As a specific example, a superhydrophobic coating (SHC) on aluminum alloy was prepared by a simple etching combined with the decoration of a low-surface-energy material. The optimal SHC has a water contact angle (CA) at ~157.4° and a sliding angle (SA) of ~8.3° due to the synergy of binary hierarchical structures and chemical modification. The SHC showed low adhesion to dry contaminants and a series of liquids, displaying a good self-cleaning effect. The SHC maintained superhydrophobicity after exposure to air and humid condition at 60 °C for 7 days. In addition, the electrochemical measurements reveal that the anti-corrosion performance was enhanced by reducing the corrosion current density (Jcorr) by 1 order of magnitude and increasing the corrosion potential (Ecorr) by 0.527 V as compared to the bare Al alloy substrate after immersion for 168 h.

Nanotube Active Water Pump Driven by Alternating Hydrophobicity

Water transport must be efficiency controlled for the future sustainability of life. Various water transport systems using carbon nanotubes have been proposed in recent years. Although these systems are more permeable than aquaporins, their water transport is passive. In this study, we successfully demonstrate an active water pump driven by simple hydrophobic interaction through computer simulation. Even in the absence of a pressure- or density-gradient, the proposed pump can actively transport water molecules by alternately switching the hydrophobicity of the pump surface. The water transport rate can be easily controlled by varying the time interval of switching. The pump with optimized switching time exhibits prominent water permeance. The results obtained herein can be applied in various water transport technologies because of the simple mechanics. The proposed water pump has the potential to realize an effective device such as a low-energy artificial purification system.

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.

Facile Fabrication of a Superhydrophobic Surface with Robust Micro-/Nanoscale Hierarchical Structures on Titanium Substrate

A superhydrophobic surface with robust structures on a metallic surface could improve its application in various harsh conditions. Herein, we developed a new strategy to fabricate robust micro-/nanoscale hierarchical structures with electrical discharge machining and electrochemical etching on a titanium substrate. After modification by fluorinated silane, the static water contact angle and slide angle of the surface could reach 162 ± 2° and 4 ± 1°, respectively. The superhydrophobic surfaces showed good corrosion resistance and mechanical stability after scratching with sandpapers. In addition, the superhydrophobic surfaces had good self-cleaning performance even in an acidic environment as well as the potential to be used as guiding tracks in droplet microfluidics and lab-on-a-chip systems. These results are expected to be helpful in designing the surface of liquid float gyroscope parts.

Nonwetting Behavior of Al-Co Quasicrystalline Approximants Owing to Their Unique Electronic Structures

Good wetting is generally observed for liquid metals on metallic substrates, while poor wetting usually occurs for metals on insulating oxides. In this work, we report unexpected large contact angles for lead on two metallic approximants to decagonal quasicrystals, namely, Al₅Co₂ and Al₁₃Co₄. Intrinsic surface wettability is predicted from first principles, using a thermodynamic model based on the Young equation, and validated by the good agreement with experimental measurements performed under ultra-high vacuum by scanning electron microscopy. The atomistic details of the atomic and electronic structures at the Pb-substrate interface, and the comparison with Pb(111)/Al(111), underline the influence of the specific electronic structures of quasicrystalline approximants on wetting. Our work suggests a possible correlation of the contact angles with the density of states at the Fermi energy and paves the way for a better fundamental understanding of wettability on intermetallic substrates, which has potential consequences in several applications such as supported catalysts, protective coatings, or crystal growth.

Facile fabrication of superhydrophobic zinc coatings with corrosion resistance via an electrodeposition process

In this investigation, we demonstrated a controlled electrodeposition method by varying the current density to generate hierarchical structures of zinc (Zn) on a carbon steel surface, which serves as a hydrophobic and anticorrosion coating when further modified by stearic acid to form a covalently bonded layer that offers low surface energy.

Superhydrophobic Civil Engineering Materials: A Review from Recent Developments

Superhydrophobic surfaces have drawn attention from scientists and engineers because of their extreme water repellency. More interestingly, these surfaces have also demonstrated an infinite influence on civil engineering materials. In this feature article, the history of wettability theory is described firstly. The approaches to construct hierarchical micro/nanostructures such as chemical vapor deposition (CVD), electrochemical, etching, and flame synthesis methods are introduced. Then, the advantages and limitations of each method are discussed. Furthermore, the recent progress of superhydrophobicity applied on civil engineering materials and its applications are summarized. Finally, the obstacles and prospects of superhydrophobic civil engineering materials are stated and expected. This review should be of interest to scientists and civil engineers who are interested in superhydrophobic surfaces and novel civil engineering materials.

Colorful Wall-Bricks with Superhydrophobic Surfaces for Enhanced Smart Indoor Humidity Control

Humidity-control materials have attracted increasing attention because of energy savings and smart regulation of indoor comforts. The current research is a successive work to face challenges, such as poor performance, limitations for large-scale production, and surface contamination. Here, we report a smart humidity-control wall-brick manufactured from sepiolite using CaCl₂ as an additive. Low-temperature sintering generated a super hygroscopic interior structure, and further silane modification produced bricks with superhydrophobic surfaces. These superhydrophobic surfaces can promote the moisture storage and prevent the CaCl₂ solution from leaking even after the surface is wiped 100 times. Meanwhile, the superhydrophobic surfaces make the wall-bricks easy to clean; also, these materials possess antifouling and antifungal properties. The 24 h and saturated moisture adsorption-desorption contents reached 630 and 1700 g·m^-2, respectively. Furthermore, a test was performed using model houses in a real environment, which indicates that the wall-bricks can narrow the daily indoor humidity fluctuations by more than 20% in both wet and dry seasons. The white wall-brick can also be dyed with different colors and thus shows promise for applications in interior decorations of houses.

Facile Fabrication of Durable Superhydrophobic Films from Carbon Nanotube/Main-Chain Type Polybenzoxazine Composites

Superhydrophobic materials have immense applications in the fields of industry and research. However, their durability is still a cause for concern. A facile method for preparing durable superhydrophobic films from carbon nanotubes (CNTs) and the main-chain type polybenzoxazine precursors is reported herein. We used probe ultrasonicator to prepare CNT/polybenzoxazine coatings. Compared with the general sonicating dispersion process, the dispersion time was greatly reduced from a few hours to 5 minutes and the prepared suspension exhibited film-forming characteristics well. The CNT/polybenzoxazine films, which do not contain any fluorinated compounds, exhibit remarkable durability against thermal treatment, organic solvents, corrosive liquids, and sandpaper abrasion, while retaining their superhydrophobicity. Furthermore, these CNT/polybenzoxazine films also showed durable superhydrophobicity after ultraviolet (UV) irradiation for 100 h. This CNT/polybenzoxazine film can be readily used for practical applications to make durable superhydrophobic coatings.

Applicable Superamphiphobic Ni/Cu Surface with High Liquid Repellency Enabled by the Electrochemical-Deposited Dual-Scale Structure

Until now, scalable fabrication and utilization of superamphiphobic surfaces based on sophisticated structures has remained challenging. Herein, we develop an applicable superamphiphobic surface with nano-Ni pyramid/micro-Cu cone structures prepared by cost-effective electrochemical deposition. More importantly, excellent dynamic wettability is achieved, exhibiting as ultralow sliding angle (∼0°), multiple droplets rebounding (13 times), and a total rejection. The supportive cushions trapped within the dual-scale micro/nanostructures is proved to be the key factor contributing to such high liquid repellency, whose existence is intuitively ascertained at both solid-air-liquid and water-solid-oil systems in this work. In addition, the enduring reliability of the wetting performance under various harsh conditions further endows the surface with broader application prospects.

Facile Fabrication of Superhydrophobic Copper- Foam and Electrospinning Polystyrene Fiber for Combinational Oil⁻Water Separation

Membrane-based metal substrates with special surface wettability have been applied widely for oil/water separation. In this work, a series of copper foams with superhydrophobicity and superoleophilicity were chemically etched using 10 mg mL⁻¹ FeCl₃/HCl solution with consequent ultrasonication, followed by the subsequent modification of four sulfhydryl compounds. A water contact angle of 158° and a sliding angle lower than 5° were achieved for the copper foam modified using 10 mM n-octadecanethiol solution in ethanol. In addition, the interaction mechanism was initially investigated, indicating the coordination between copper atoms with vacant orbital and sulfur atoms with lone pair electrons. In addition, the polymeric fibers were electrospun through the dissolution of polystyrene in a good solvent of chlorobenzene, and a nonsolvent of dimethyl sulfoxide. Oil absorption and collection over the water surface were carried out by the miniature boat made out of copper foam, a string bag of as-spun PS fibers with high oil absorption capacity, or the porous boat embedded with the as-spun fibers, respectively. The findings might provide a simple and practical combinational method for the solution of oil spill.

Environmentally Benign Production of Stretchable and Robust Superhydrophobic Silicone Monoliths

Superhydrophobic materials hold an enormous potential in sectors as important as aerospace, food industries, or biomedicine. Despite this great promise, the lack of environmentally friendly production methods and limited robustness remain the two most pertinent barriers to the scalability, large-area production, and widespread use of superhydrophobic materials. In this work, highly robust superhydrophobic silicone monoliths are produced through a scalable and environmentally friendly emulsion technique. It is first found that stable and surfactantless water-in-polydimethylsiloxane (PDMS) emulsions can be formed through mechanical mixing. Increasing the internal phase fraction of the precursor emulsion is found to increase porosity and microtexture of the final monoliths, rendering them superhydrophobic. Silica nanoparticles can also be dispersed in the aqueous internal phase to create micro/nanotextured monoliths, giving further improvements in superhydrophobicity. Due to the elastomeric nature of PDMS, superhydrophobicity can be maintained even while the material is mechanically strained or compressed. In addition, because of their self-similarity, the monoliths show outstanding robustness to knife-scratch, tape-peel, and finger-wipe tests, as well as rigorous sandpaper abrasion. Superhydrophobicity was also unchanged when exposed to adverse environmental conditions including corrosive solutions, UV light, extreme temperatures, and high-energy droplet impact. Finally, important properties for eventual adoption in real-world applications including self-cleaning, stain-repellence, and blood-repellence are demonstrated.

Facile Fabrication and Characterization of a PDMS-Derived Candle Soot Coated Stable Biocompatible Superhydrophobic and Superhemophobic Surface

We report a simple, inexpensive, rapid, and one-step method for the fabrication of a stable and biocompatible superhydrophobic and superhemophobic surface. The proposed surface comprises candle soot particles embedded in a mixture of PDMS+n-hexane serving as the base material. The mechanism responsible for the superhydrophobic behavior of the surface is explained, and the surface is characterized based on its morphology and elemental composition, wetting properties, mechanical and chemical stability, and biocompatibility. The effect of %n-hexane in PDMS, the thickness of the PDMS+n-hexane layer (in terms of spin coating speed) and sooting time on the wetting property of the surface is studied. The proposed surface exhibits nanoscale surface asperities (average roughness of 187 nm), chemical compositions of soot particles, very high water and blood repellency along with excellent mechanical and chemical stability and excellent biocompatibility against blood sample and biological cells. The water contact angle and roll-off angle is measured as 160° ± 1° and 2°, respectively, and the blood contact angle is found to be 154° ± 1°, which indicates that the surface is superhydrophobic and superhemophobic. The proposed superhydrophobic and superhemophobic surface offers significantly improved (>40%) cell viability as compared to glass and PDMS surfaces.