Versatile nonfluorinated superhydrophobic coating with self-cleaning, anti-fouling, anti-corrosion and mechanical stability

Wettability behavior of DTMS modified SiO2: Experimental and molecular dynamics study

In this research, the wetting behavior of SiO2 modified with dodecyltrimethoxysilane (DTMS) was explored using both experimental and molecular dynamics (MD) simulation approaches. The experimental results reveal that DTMS can chemically bond to the SiO2 surface, and the contact angle (CA) reaches the maximum value of 157.7° when the mass of DTMS is twice that of SiO2. The different wetting behaviors caused by DTMS grafting were analyzed by CA fitting, ionic pairs, concentration distribution, molecule orientation, and interfacial interaction energy. The results demonstrate that a 25 % DTMS grafting rate resulted in a maximum CA of 158.2°, which is ascribed to the disruption of interfacial hydrogen bonding and changes in the hydration structure caused by DTMS grafting. Moreover, the above hydrophobic SiO2 model shows a slight decrease in CA as the water temperature increases, which is consistent with the experimental findings. In contrast, an opposite change was observed for the pristine SiO2 model. Although the higher water temperature enhances the diffusion capacity of water molecules in both models, the difference in interfacial interactions is responsible for the change in CA. We hope this finding will contribute to a deeper understanding of the wetting adjustment of SiO2.

Durable Self-Cleaning Radiative Cooling Coatings for Building Energy Efficiency

Passive daytime radiative cooling (PDRC) is an energy-saving technology without an additional energy supply or environmental pollution. At present, most PDRC coatings for buildings are only aiming at high solar reflectivity (RS) and high mid-infrared emissivity (EMIR) while ignoring practicalities such as adhesion strength, scalability, and durability. In this work, modified calcined kaolin/(ethylene trifluorochloroethylene copolymer-polydimethylsiloxane) (MK/(FEVE-PDMS)) coating with super practicability is prepared by using MK as a filler, FEVE as an adhesive, and PDMS as a hydrophobic modifier. The RS and EMIR of the coating are 92.5 and 94.6%, respectively. The MK/(FEVE-PDMS) coating exhibits superhydrophobicity, with an advancing contact angle (ACA) of 160.2° and a hysteresis contact angle of 7.3°. At an average solar irradiance of 742.78 W m-2, the coating achieved a temperature drop of 13.12 °C (shielded with PE film) and 3.09 °C (without shielding), respectively, relative to the environment. The coating adheres firmly to the substrate with an adhesion strength of class 2. The superhydrophobicity of the coating provides excellent durability and ease of repair, which can resist UV aging and mechanical damage. The durable superhydrophobicity gives the coating long-term stability in PDRC performance. Additionally, the cheap raw materials and the preparation process, consistent with the production of existing paints, show excellent scalability. Moreover, the energy consumption simulation results show that the energy saving ratio of the coating is more than 10% in the densely populated Yangtze River Delta and Pearl River Delta. The durable self-cleaning radiative coating developed in this work has potential application prospects in areas where the demand for cooling in summer is large and the demand for heating in winter is small.

A comprehensive review on anticorrosive/antifouling superhydrophobic coatings: Fabrication, assessment, applications, challenges and future perspectives

Superhydrophobicity (SHP) is an incredible phenomenon of extreme water repellency of surfaces ubiquitous in nature (E.g. lotus leaves, butterfly wings, taro leaves, mosquito eyes, water-strider legs, etc). Historically, surface exhibiting water contact angle (WCA) > 150° and contact angle hysteresis <10° is considered as SHP. The SHP surfaces garnered considerable attention in recent years due to their applications in anti-corrosion, anti-fouling, self-cleaning, oil-water separation, viscous drag reduction, anti-icing, etc. As corrosion and marine biofouling are global problems, there has been focused efforts in combating these issues using innovative environmentally friendly coatings designs taking cues from natural SHP surfaces. Over the last two decades, though significant progress has been made on the fabrication of various SHP surfaces, the practical adaptation of these surfaces for various applications is hampered, mainly because of the high cost, non-scalability, lack of simplicity, non-adaptability for a wide range of substrates, poor mechanical robustness and chemical inertness. Despite the extensive research, the exact mechanism of corrosion/anti-fouling of such coatings also remains elusive. The current focus of research in recent years has been on the development of facile, eco-friendly, cost-effective, mechanically robust chemically inert, and scalable methods to prepare durable SHP coating on a variety of surfaces. Although there are some general reviews on SHP surfaces, there is no comprehensive review focusing on SHP on metallic and alloy surfaces with corrosion-resistant and antifouling properties. This review is aimed at filling this gap. This review provides a pedagogical description with the necessary background, key concepts, genesis, classical models of superhydrophobicity, rational design of SHP, coatings characterization, testing approaches, mechanisms, and novel fabrication approaches currently being explored for anticorrosion and antifouling, both from a fundamental and practical perspective. The review also provides a summary of important experimental studies with key findings, and detailed descriptions of the evaluation of surface morphologies, chemical properties, mechanical, chemical, corrosion, and antifouling properties. The recent developments in the fabrication of SHP -Cr-Mo steel, Ti, and Al are presented, along with the latest understanding of the mechanism of anticorrosion and antifouling properties of the coating also discussed. In addition, different promising applications of SHP surfaces in diverse disciplines are discussed. The last part of the review highlights the challenges and future directions. The review is an ideal material for researchers practicing in the field of coatings and also serves as an excellent reference for freshers who intend to begin research on this topic.

Corn straw lignin - A sustainable bioinspired finish for superhydrophobic and UV-protective cellulose fabric

Hydrophobic textiles have been considered extensively for self-cleaning, phase-separating, and biomedical curing applications. We focused on preparing an eco-friendly lignin-based bio-finish to develop superhydrophobic cellulose fabric under mild conditions. The mass spectroscopic analysis expressed that the lignin comprised the major constituents of p-coumaryl alcohol, ferulic acid, coniferyl alcohol, and sinapyl alcohol. The surface morphological analysis indicated the formation of a regular lignin coating on the cellulose fabric. The bio-finished cellulose fabric prepared (at 2 %, w/v, lignin) expressed the maximum water contact angle (WCA) of 157.2° and remained in the hydrophobic range (119°) after ten standard washes. The treated fabric expressed the WCA values of 135.0 and 133.0° after exposure to pH 2 and 12 aqueous media, respectively. The infrared spectroscopic analysis indicated the functional chemistry of the precursors involved and possible alteration in their chemical interactions during processing. The lignin-treated cellulose was observed to be less crystalline as compared to the untreated one. Such fabric expressed acceptable comfort, sensorial properties, and thermal stability up to 333 °C. The treated fabrics could block up to 92.24 % UV-A and 98.62 % UV-B radiations. Consequently, the lignin-based finish sourced from wasted corn straw was found cost-effective and efficient for producing superhydrophobic cellulose fabric.

Multifunctional liquid-like magnetic nanofluids mediated coating with anticorrosion and self-healing performance

The long-term protective efficacy of organic coatings against corrosion can be diminished by the presence of micropores/cracks and poor self-healing capabilities. To address these issues, Ti3C2 MXene was subjected to liquefaction-like treatment to maintain a two-dimensional lamellar structure in water and polymer matrix for a long time, as well as improve the dispersion stability and loading capacity of MXene. The inorganic corrosion inhibitor ferroferric oxide (Fe3O4) was then electrostatically loaded onto MXene nanofluids to obtain a hybrid material. Through hydrogen bonding, polyvinyl alcohol (PVA) molecular chains were bridged to the hybrid material, resulting in a self-healing anti-corrosion coating. The coating exhibited excellent corrosion protection, as well as self-healing properties attributed to the labyrinth effect and corrosion inhibition of MXene@Fe3O4 hybrids. Notably, electrochemical testing demonstrated outstanding corrosion resistance of this coating on diverse substrate surfaces. In addition, the anti-corrosion coating will strongly coalesce on the surface of B-NdFeB under magnetic stimulation, realizing the localized corrosion protection of metal materials. The anti-corrosion coating can be quickly repaired under the stimulation of water as well as recovery, the anti-corrosion repair efficiency on the surface of permanent magnets is up to 92%, and the mechanical properties after recovery can be restored to 97% of the original sample. This innovative coating offers a convenient, green synthesis strategy for the construction of self-healing coatings with superior anti-corrosion properties.

HD-SiO2/SiO2 Sol@PDMS Superhydrophobic Coating with Good Durability and Anti-Corrosion for Protection of Al Sheets

Superhydrophobic coatings with excellent water-repellent properties imply a wide range of application areas. However, improvements are needed in terms of stability and complex processing procedures. In the present study, a superhydrophobic coating on Al sheets was prepared by mixing hexadecyltrimethoxysilane (HDTMS)-modified SiO₂ nanoparticles and acid-catalyzed silica sols (HD-SiO₂/SiO₂ Sol) with polydimethylsiloxane (PDMS) binder. The HD-SiO₂ nanoparticles and acid-catalyzed silica sol (SiO₂ sol) form a binary graded micro-nanostructure, providing excellent superhydrophobicity (Water Contact Angle = 158.5°, Sliding angle = 0°). Superhydrophobic coatings with excellent water-repellent properties have potential for corrosion prevention. However the commonly used organic resins have poor chemical and mechanical properties. In the present study, the results of outdoor exposure for 30 days, immersion in acid and alkaline solutions for 24 h, grit abrasion, and water impact experiments, respectively, showed that the prepared superhydrophobic coating has good wear resistance. The integrated superhydrophobic coating on the Al sheets exhibited good corrosion inhibition with an efficiency (η) of 98.9%, which is much higher than that of the uncoated sheets. The present study provides a promising approach for producing stable superhydrophobic coatings at a low cost, with the potential to supplant conventional organic resin anti-corrosion coatings.

Construction and Performance of Superhydrophobic Surfaces for Rusted Iron Artifacts

Ancient iron artifacts need to be protected with a rust layer, often stabilized by tannic acid corrosion inhibition. In humid environments, water vapor could slowly penetrate and trigger galvanic corrosion of metal artefacts. Sealing treatments are generally applied to the artefact surface to isolate water and enhance its corrosion resistance. Superhydrophobic modifications could effectively block the penetration of moisture into the interior of the artefact and provide a nice water barrier. Stearic acid with tannic acid inhibition treatment creates a superhydrophobic protective layer on the surface of rusted iron artifacts and enhances corrosion resistance effectively. Various scientific analyses and testing methods are used in this paper to evaluate the corrosion resistance of rusted surfaces after superhydrophobic modification and investigate the reaction mechanisms. The results indicate that the contact angle of the rusted surface after corrosion inhibition by tannic acid and modified by stearic acid is increased to 152.2°, which means the superhydrophobic protective layer has been successfully constructed. The C/Fe ratio of the rusted surface is increased from 0.21 to 2.10, and the characteristic diffraction peaks of O1s and Fe 2p_3/2 shift toward higher binding energy. Stearic acid is combined with the corrosion product layer by chemical bonding. Chelation between rust products, tannic acid, and steric acid is effective, and the chelate is chemically stable. The superhydrophobic surface forms a lamellar wax-like layer as an air barrier to isolate liquid water, resulting in a significant decrease in corrosion current and an increase in Warburg impedance to 217.9 times the original state, with a protection efficiency of 88.3%. Tannic acid corrosion inhibition and stearic acid superhydrophobic modification have an excellent synergistic protective effect on improving the corrosion resistance of iron artifacts, resulting in better corrosion resistance of iron artifact materials. The research provides new ideas and references for the protection of ancient iron artifacts sealing.

Preparation and corrosion resistance of superhydrophobic Ni-Co-Al2O3 coating on X100 steel

X100 steel is easy to be corroded because of the high salt content in alkaline soils. The Ni-Co coating can slow down the corrosion but still cannot meet the requirements of modern demands. Based on this, in this study, on the basis of adding Al₂O₃ particles to the Ni-Co coating to strengthen its corrosion resistance, combined with superhydrophobic technology to inhibit corrosion, a micro/nano layered Ni-Co-Al₂O₃ coating with a new combination of cells and papillae was electrodeposited on X100 pipeline steel, and superhydrophobicity was integrated into it using a low surface energy modification method to improve wettability and corrosion resistance. SEM, XRD, XPS, FTIR spectroscopy, contact angle, and an electrochemical workstation were used to investigate the superhydrophobic materials' microscopic morphology, structure, chemical composition, wettability, and corrosion resistance. The co-deposition behavior of nano Al₂O₃ particles can be described by two adsorption steps. When 15 g L^-1 nano Al₂O₃ particles were added, the coating surface became homogeneous, with an increase in papilla-like protrusions and obvious grain refinement. It had a surface roughness of 114 nm, a CA of 157.9° ± 0.6°, and -CH₂ and -COOH on its surface. The corrosion inhibition efficiency of the Ni-Co-Al₂O₃ coating reached 98.57% in a simulated alkaline soil solution, and the corrosion resistance was significantly improved. Furthermore, the coating had extremely low surface adhesion, great self-cleaning ability, and outstanding wear resistance, which was expected to expand its application in the field of metal anticorrosion.

Improving the Corrosion Resistance of Aluminum Alloy by Creating a Superhydrophobic Surface Structure through a Two-Step Process of Etching Followed by Polymer Modification

A multifunctional aviation aluminum alloy with good superhydrophobicity and corrosion resistance was prepared by a two-step process of etching followed by polymer modification. Meanwhile, micro- and nanostructures formed on the processed sample. Compared with bare sample, the static liquid contact angle on the as-prepared sample was increased by 100.8°. Further polarization tests showed that the corrosion potential of such a sample increased, and the corrosion current density decreased obviously, thus suggesting that the corrosion resistance of the modified sample was significantly improved. The same conclusion was confirmed by subsequent impedance testing. The work is of great economic value and practical significance to enhance the corrosion resistance of aviation actuator materials and also lays a foundation for future hydrophobic application research in aeronautical engineering.

Electrical Discharge Coating a Potential Surface Engineering Technique: A State of the Art

Electrical discharge coating (EDC) process is used to deposit material on workpiece surface from sacrificial or green compact tool electrode in an electrical discharge machine. The paper presents the mechanism of EDC using green compact electrode and powder mixed dielectric methods. The tool electrode material, electrode size, process parameters, and type of dielectrics can directly affect the surface integrity of workpiece. Here, a process map of EDC as a function of process parameters, its classification, advantages, and applications for a wide range of engineering materials offers a proper template for the evaluation of coating phenomena. This study shows that EDC is an economic process as compared to other costlier techniques. Additionally, the effect of various EDM and EDC parameters on surface integrity and tribological behavior of deposited coatings is studied with their pros and cons. Finally, the current research trends of EDC and its challenges are elaborated.

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.

Selective Fabrication of Robust and Multifunctional Super Nonwetting Surfaces by Diverse Modifications of Zirconia-Ceria Nanocomposites

The creation of surfaces with various super nonwetting properties is an ongoing challenge. We report diverse modifications of novel synthesized zirconia-ceria nanocomposites by different low surface energy agents to fabricate nanofluids capable of regulating surface wettability of mineral substrates to achieve selective superhydrophobic, superoleophobic-superhydrophilic, and superamphiphobic conditions. Surfaces treated with these nanofluids offer self-cleaning properties and effortless rolling-off behavior with sliding angles ≤7° for several liquids with surface tensions between 26 and 72.1 mN/m. The superamphiphobic nanofluid coating imparts nonstick properties to a solid surface whereby liquid drops can be effortlessly displaced on the coating with a near-zero tilt and conveniently lifted off using a needle tip, leaving no trace. Further, the superamphiphobic surface demonstrates good oil repellency toward ultralow surface tension liquids such as n-hexane and n-heptane. The superoleophobic-superhydrophilic surface repels oil droplets well regardless of whether it is in the air or underwater conditions. In addition, reaping the benefits of the ZrO₂-CeO₂ nanocomposites' photocatalysis feature, the superoleophobic-superhydrophilic coating exhibits self-cleaning ability by the degradation of color dyes. Modification of the wettability of substrates is carried out by a cost-effective and facile solution-immersion approach, which creates surfaces with hierarchical nano-submicron-scaled structures. The multipurpose coated surfaces have outstanding durability and mechanical stability. They also resist well high-temperature-high-pressure conditions, which will provide various practical applications in different fields, including the condensate banking removal in gas reservoirs or the separation of oil/water mixtures.

The Effect of Eco-Friendly Inhibitors on the Corrosion Properties of Concrete Reinforcement in Harsh Environments

In the present research, the synergistic effect of Arabic and guar gum inhibitors on the corrosion efficiency of concrete reinforcement was investigated. Thus, eight types of Arabic and guar gum combinations with 100, 250, 500, 750, and 1000 ppm were added to the steel reinforcement for 1, 7, 28, 48, and 72 days. The corrosion behavior of the samples was investigated by the electrochemical impedance (EIS) test. Water transmissibility, electrical resistivity, and compressive strength of concrete were also studied. The results showed that adding inhibitors generally increased the compressive strength of concrete. It was also found that water transmissibility was reduced by the addition of inhibitors. The electrical resistivity of the samples increased slightly with increasing time up to 72 days. EIS and Tafel results have demonstrated that Arabic and guar gums are effective inhibitors for reinforced concrete structures. Furthermore, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) utilized to analyze the samples indicated that inhibitor grain size was enhanced by enhancing the concentration of the inhibitor combination, showing that the guar and Arabic inhibitor combinations were properly absorbed on the reinforcement surface. Results showed that a sample with 250 ppm Arabic gum and 250 ppm guar gum having a properly distributed inhibitor combination on the reinforcement surface creates a desirable cathode current.

Role of Substrate Type in the Process of Polyelectrolyte Multilayer Formation

Polyelectrolyte multilayers are coatings formed by the alternate deposition of polycations and polyanions on a charged surface. In this study we examined how the type of substrate affects a multilayer prepared from poly(allylamine hydrochloride) and poly(acrylic acid). Silicon and titanium wafers were used as substrates. Their properties were systematically studied using ellipsometry, tensiometry, atomic force microscopy and streaming potential measurements. Multilayers were built up at pH = 7 with tetramethylammonium chloride as the background salt. The growth of films was monitored by ellipsometry, while the morphology and surface roughness were determined by atomic force microscopy. It was found that the thickness of multilayers containing 10 layers on silicon is 10 nm, whereas the thickness of the same film on titanium is three times higher. It was shown that multilayers formed on silicon display a grain-like structure, which was not the case for a film formed on titanium. Such morphological properties are also reflected in the surface roughness. Finally, it was shown that, in addition to the electrostatic interactions, the hydrophobicity of the substrate also plays an important role in the polyelectrolyte multilayer formation process and influences its thickness and properties.

Effect of Psyllium Husk Addition on the Structural and Physical Properties of Biodegradable Thermoplastic Starch Film

The research subject was the analysis of the microstructure, barrier properties, and mechanical resistance of the psyllium husk (PH)-modified thermoplastic starch films. The tensile tests under various static loading conditions were not performed by researchers for this type of material before and are essential for a more precise assessment of the material’s behavior under the conditions of its subsequent use. The film samples were manufactured by the casting method. PH addition improved starch gelatinization and caused a decrease in failure strain by 86% and an increase in failure stress by 48% compared to pure films. Fourier transform infrared spectroscopy results showed the formation of additional hydrogen bonds between polysaccharides in starch and PH. An increase in the number of hydrophilic groups in the modified films resulted in a faster contact angle decrease (27.4% compared to 12.8% for pure ones within the first 5 s); however, it increased the energy of water binding and surface complexity. The modified films showed the opacity at 600 nm, 43% higher than in the pure starch film, and lower transmittance, suggesting effectively improving barrier properties to UV light, a potent lipid-oxidizing agent in food systems.