Search Results (99)

Superhydrophobic coatings possess distinct wettability characteristics and hold significant potential in metal corrosion protection and underwater drag reduction. However, their practical application is often hindered by poor durability arising from the fragility of their micro/nanostructured surface roughness. In this study, a durable superhydrophobic coating featuring a hierarchical, hydrangea-like micro/nanostructure was successfully fabricated on an aluminum alloy substrate via a simple one-step cold-spraying technique. The coating consisted of hydrangea-shaped SiO₂ nanoparticles modified with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFDT) to produce multiscale roughness, while epoxy resin (EP) served as the binding matrix to enhance mechanical integrity. The hydrangea-like SiO₂ nanostructures were characterized by solid cores and wrinkled, petal-like outgrowths. This unique morphology not only increased the surface roughness but also provided more active sites for air entrapment, thereby enhancing the coating’s overall performance. The h-SiO₂@PFDT-EP composite coating exhibited excellent superhydrophobicity, with a WCA of 170.1° ± 0.8° and a SA of 2.7° ± 0.5°. Durability was evaluated through sandpaper abrasion, tape peeling, acid and alkali immersion, artificial weathering, and salt spray tests. The results demonstrated that the coating retained stable superhydrophobic performance under various environmental stresses. Compared with bare 6061 aluminum and EP coatings, its corrosion current density was reduced by four and three orders of magnitude, respectively. Furthermore, the coating achieved a maximum drag-reduction rate of 31.01% within a velocity range of 1.31–7.86 m/s. The coating also displayed excellent self-cleaning properties. Owing to its outstanding durability, corrosion resistance, and drag-reducing capability, this one-step fabricated superhydrophobic coating showed great promise for applications in marine engineering and defense. Full article

A superhydrophobic surface with hierarchical micro/nano-array structures was successfully fabricated on 6061 aluminum alloy through a combination of femtosecond laser etching and anodic oxidation. Femtosecond laser etching formed a regularly arranged microscale “pit-protrusion” array on the aluminum alloy surface. After modification with a fluorosilane ethanol solution, the surface exhibited superhydrophobicity with a contact angle of 154°. Subsequently, the anodic oxidation process formed an anodic oxide film dominated by an array of aluminum oxide (Al₂O₃) nanopores at the submicron scale. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses revealed that the nanopore structures uniformly and continuously covered the laser-ablated layer. This hierarchical structure significantly increased the surface water contact angle to 162°. Wettability analysis showed that the prepared composite coating formed an air layer accounting for 91% of the surface area. Compared with the sample only treated by femtosecond laser etching, the presence of the Al₂O₃ nanopore structure significantly enhanced the mechanical durability, superhydrophobic durability, and corrosion resistance of the superhydrophobic surface. The proposed multi-step fabrication strategy offers an innovative method for creating multifunctional, durable superhydrophobic coatings and has important implications for their large-scale industrial use. Full article

The spreading and rebound of impacting droplets on superhydrophobic interfaces is a complex phenomenon governed by the interconnected contributions of surface, fluid and environmental factors. In this work, we employed a collection of 1498 water–glycerin droplet impact experiments on monolayer-functionalized laser-structured aluminum samples to train, validate and optimize a machine learning regression model. To elucidate the role of each influential parameter, we analyzed the model-predicted individual parameter contributions on key descriptors of the phenomenon, such as contact time, maximum spreading coefficient and rebound efficiency. Our results confirm the dominant contribution of droplet impact velocity while highlighting that the droplet spreading phase appears to be independent of surface microtopography, i.e., the depth and width of laser-made features. Interestingly, once the rebound transitions to the retraction stage, the importance of the unwetted area fraction is heightened, manifesting in higher rebound efficiency on samples with smaller distances between laser-fabricated microchannels. Finally, we exploited the trained models to develop empirical correlations for predicting the maximum spreading coefficient and rebound efficiency, both of which strongly outperform the currently published models. This work can aid future studies that aim to bridge the gap between the observed macroscale surface-droplet interactions and the microscale properties of the interface or the thermophysical properties of the fluid. Full article

Dew collection is one of the most efficient water harvesting methods. In this work, we experimentally investigated the effects of modified nanostructured surfaces on water harvesting performance. Aluminum surfaces exhibiting hydrophobic, superhydrophobic, hydrophilic, and biphilic properties were utilized in this study. The superhydrophobic surface was fabricated using a fluorinated modified silica nanoparticles coating, while nanolaser processing and the surface abrasion with sandpapers were employed to create two distinct hydrophilic structures. In addition, various biphilic surface patterns, incorporating both superhydrophobic and hydrophilic characteristics, were also fabricated. The nanolaser-treated surface demonstrated the highest water harvesting performance, achieving a water collection of 386.7 mL/m². This performance represented a 42% increase compared to unpolished sample and a 282% increase relative to the superhydrophobic sample. Furthermore, the results indicated that the optimal biphilic surface pattern occurred at a 1:4 superhydrophobic-to-hydrophilic area ratio. The experimental outcomes were further interpreted through the mechanisms underlying water harvesting. Additionally, the experimental results were explained with the water harvesting mechanism. Full article

Laser surface texturing (LST) is a versatile method for enhancing material surface properties, offering high precision and flexibility for surface modification. This review comprehensively examines the application of laser texturing technology for surface protection and functional regulation of aluminum alloys, focusing on wettability, anti-icing, corrosion resistance, and wear resistance. It highlights recent progress in laser surface patterning techniques, describing the principles and attributes of methods such as direct laser writing, laser interference patterning, and laser shock treatment. The influence of laser intensity, scanning velocity, and texture spacing on surface topography is discussed thoroughly. Mechanisms of wettability control via laser surface texturing are summarized, emphasizing the key factors required to achieve superhydrophobic or hydrophilic properties through texture design. Advancements in enhancing anti-icing, anti-frost, anti-fouling, and anti-corrosion properties through multi-scale textures and their synergistic effects with functional coatings are analyzed. Additionally, the enhancement of wear resistance and friction performance under both dry and lubricated conditions is reviewed, with a focus on how the geometry and arrangement of textures affect the coefficient of friction and wear rate. Finally, the paper addresses challenges and future directions, including process optimization, scalability, and the integration of LST with advanced coatings to maximize its potential in aluminum alloy applications. Full article

In this study, an acid–base proton transfer method was used to fabricate functional coatings on Mg surfaces with the cooperative effect of durable superhydrophobic and exceptional self-cleaning properties, providing high-efficiency corrosion protection. In this context, aluminum chloride served as a precursor for the direct growth of aluminum hydroxide on the Mg surface. Without the addition of any solvent, the densely arranged absolute palmitic acid was strongly bonded to the grown aluminum hydroxide on the Mg substrate, which acted as an effective anti-water barrier that can impede the penetration of water, as well as the oxygen and chloridion involved. Full article

In this work, the simple fabrication of a new superhydrophobic magnetic sponge based on CNTs, NiFe₂O₄ nanoparticles, and PDMS was investigated. CNTs were synthesized by chemical vapor deposition (CVD) on a nickel ferrite catalyst supported on aluminum oxide (NiFe₂O₄/Al₂O₃). The synthesis of nickel ferrite (NiFe) was accomplished using the sol–gel method, yielding magnetic nanoparticles (43 Am²kg⁻¹, coercivity of 93 Oe, 21–29 nm). A new superhydrophobic magnetic PU/CNT/NiFe₂O₄/PDMS sponge was fabricated using a polyurethane (PU) sponge, CNTs, NiFe₂O₄ nanoparticles, and polydimethylsiloxane (PDMS) through the immersion coating method. The new PU/CNT/NiFe₂O₄/PDMS sponge exhibits excellent superhydrophobic/oleophilic/mechanical properties and water repellency (water absorption rate of 0.4%) while having good absorption of oil, olive oil, and organic liquids of different densities (absorption capacity of 21.38 to 44.83 g/g), excellent separation efficiency (up to 99.81%), the ability to be reused for removing oil and organic solvents for more than 10 cycles, and easy control and separation from water using a magnet. The new PU/CNT/NiFe₂O₄/PDMS sponge is a promising candidate as a reusable sorbent for collecting oil and organic pollutants and can also be used as a hydrophobic filter due to its excellent mechanical properties. Full article

In order to further improve the corrosion resistance of 7075-T6 aluminum alloy after shot peening, corrosion-resistant superhydrophobic coatings (EP-HDTMS@SiO₂) containing epoxy resin (EP), cetyltrimethoxysilane (HDTMS), and nano-silica (SiO₂) were prepared by a simple spraying method on the surface of shot-peened AA 7075-T6 aluminum alloy. The effects of different EP/SiO₂ mass ratios on the micro-morphology, surface wettability, and corrosion resistance of the superhydrophobic composite coatings were analyzed. Due to the combination of microstructure and the modification of low surface energy organics, the contact angle of EP-HDTMS@SiO₂ coatings reached the superhydrophobic level (152.6°). The electrochemical tests showed that the corrosion current densities (I_corr) of the EP-HDTMS@SiO₂ composite coatings were both significantly lower than those of the EP-HDTMS coatings and matrix aluminum alloys. The addition of SiO₂ nanoparticles could improve the hydrophobicity and corrosion resistance of epoxy-based composite coatings. Due to the increase in surface roughness and epoxy resin, the shot-peened AA 7075-T6 alloy coating had high adhesion after the peel test. The prepared coatings also showed excellent corrosion resistance in the neutral salt spray test. This study provides a simple method for preparing stable superhydrophobic coatings on metal surfaces, which is expected to expand the application of 7075 aluminum alloy in harsh environments. Full article

Laser shock ablation is incorporated into laser shock imprinting for the fabrication of papillary composite microstructures on aluminum surfaces. The primary papillary structures are fabricated using laser shock imprinting. Subsequently, secondary structures were fabricated on the surface of these primary structures using laser shock ablation, forming composite papillary microstructures. The influence of various laser shock ablation process parameters on the formation effect of these papillary composite microstructure surfaces was investigated. The results indicate that both laser shock energy and shock frequency affect the integrity of the secondary microstructure coverage on the material surface, the height of the composite microstructure, and the surface morphology. Through comparative optimization, the optimal process parameters were determined to be 675 mJ of energy and one shock ablation. Additionally, the differences in the flow behavior of metallic materials between the center and the periphery of the beam spot, caused by the shock wave, were analyzed. The wettability of the composite microstructure aluminum surface was also explored. The variation mechanism of wettability was explained by detecting changes in the contact angle on the aluminum surface at different time intervals and analyzing changes in surface chemical composition before and after aging. Specifically, after laser shock ablation, the aluminum surface contains a large number of polar groups, making it hydrophilic. During aging treatment, these polar groups continuously adsorb non-polar alkyl organic compounds, eventually leading to hydrophobicity, with a stabilized average surface contact angle of 143°. Fluorination treatment can further achieve superhydrophobicity, with a contact angle of 151° achieved shortly after processing the composite microstructure aluminum surface. Full article

This study investigates the characterization and performance of self-cleaning TiO₂ surfaces synthesized through a one-step preparation process, followed by enhancement via plasma treatment. The process involved coating aluminum foil with an acrylic paint mixture containing nanoparticles of different mass compositions and subsequent plasma treatment using a continuous plasma arc. Scanning electron microscopy revealed the morphology of the treated surfaces, showing an increase in surface area of plasma-treated materials. Energy-dispersive X-ray spectroscopy revealed changes in oxygen and titanium in acrylic paint/TiO₂ surfaces as the TiO₂ content increased, indicating successful TiO₂ incorporation. Raman spectroscopy showed that the bulk structure of self-cleaning acrylic paints is mainly preserved after plasma treatment. Alternating current impedance spectroscopy assessed that plasma treatment reduced agglomeration and increased active sites, especially for the acrylic paint/TiO₂ surfaces with 0.5 mg/cm³ TiO₂. The contact angle measurements indicated that plasma treatment enhanced the superhydrophobic characteristics and potential self-cleaning abilities of produced acrylic paint/TiO₂ surfaces. The efficacy of these plasma-treated surfaces in self-cleaning was evaluated by testing their performance against puddle sediment and automotive oil samples. The study demonstrated that plasma treatment positively impacted the self-cleaning ability of the acrylic paint/TiO₂ surfaces, particularly those with 0.5 mg/cm³ TiO₂. This enhancement was attributed to the formation of functional groups, improved water repellency, and possible increases in surface area, which collectively contribute to the sustainable self-cleaning properties of the treated surfaces. Full article

Superhydrophobic coatings have great potential to mitigate ice accumulation and ice adhesion issues due to their outstanding water-repellent and self-cleaning characteristics. In the present study, polyurethane elastomer (PUE) is considered a superhydrophobic coating material for anti-icing applications. The life cycle assessment (LCA) of bare aluminum and PUE-coated systems is performed using the Centrum voor Milieukunde Leiden methodology. The cradle-to-gate LCA scope is implemented to evaluate and compare the total environmental impact. This study revealed that the PUE-coated system exhibited a significant reduction in total environmental impact compared to bare aluminum. The levelized cost of coating analysis demonstrates that the PUE coating system is more economical than bare aluminum surfaces. There is scope to reduce the environmental impact associated with PUE-coated systems using bio-based and less toxic chemicals/solvents. Full article

Mitigating the adverse effects of corrosion failure and low-temperature icing on aluminum (Al) alloy materials poses significant research challenges. The facile fabrication of bioinspired superhydrophobic materials offers a promising solution to the issues of corrosion and icing. In this study, we utilized laboratory-collected candle soot (CS), hydrophobic fumed SiO₂, and epoxy resin (EP) to create a HF-SiO₂@CS@EP superhydrophobic coating on Al alloy surfaces using a spray-coating technique. Various characterization techniques, including contact angle meter, high-speed camera, FE-SEM, EDS, FTIR, and XPS, were employed to investigate surface wettability, morphologies, and chemical compositions. Moreover, a 3.5 wt.% NaCl solution was used as a corrosive medium to evaluate the corrosion resistance of the uncoated and coated samples. The results show that the capacitive arc radius, charge transfer resistance, and low-frequency modulus of the coated Al alloy significantly increased, while the corrosion potential (E_corr) shifted positively and the corrosion current (I_corr) decreased by two orders of magnitude, indicating improved corrosion resistance. Additionally, an investigation of ice formation on the coated Al alloy at −10 °C revealed that the freezing time was 4.75 times longer and the ice adhesion strength was one-fifth of the uncoated Al alloy substrate, demonstrating superior delayed icing and reduced ice adhesion strength performance. Full article

Freshwater shortage is a growing problem. Inspired by the Sarracenia trichome fog-trapping and ultrafast water-transport structure, a series of hierarchical textured surfaces with high-low ribs with different wettabilities was prepared based on laser processing combined with dip modification. Through fog-collection performance tests, it was found that the samples with superhydrophobicity and low adhesion had the best fog-collection effect. In addition, it was observed that the fog-collection process of different microstructured samples was significantly different, and it was analysed that the fog-collection process was composed of two aspects: directional condensation and directional transport of droplets, which were affected by the low ribs number and rib height ratio. A design parameter was given to create the Sarracenia trichome-like structure to achieve a fast water transport mode. This study provides a good reference for the development and preparation of fog-collection surfaces. Full article

The effect of extreme water repellency, called the lotus effect, is caused by the formation of a Cassie–Baxter state in which only a small portion of the wetting liquid droplet is in contact with the surface. The rest of the bottom of the droplet is in contact with air pockets. Instrumental methods are often used to determine the textural features that cause this effect—scanning electron and atomic force microscopies, profilometry, etc. However, this result provides only an accurate texture model, not the actual information about the part of the surface that is wetted by the liquid. Here, we show a practical method for estimating the surface fraction of texture that has contact with liquid in a Cassie–Baxter wetting state. The method is performed using a set of ethanol–water mixtures to determine the contact angle of the textured and chemically equivalent flat surfaces of AlSI 304 steel, 7500 aluminum, and siloxane elastomer. We showed that the system of Cassie–Baxter equations can be solved graphically by the wetting diagrams introduced in this paper, returning a value for the texture surface fraction in contact with a liquid. We anticipate that the demonstrated method will be useful for a direct evaluation of the ability of textures to repel liquids, particularly superhydrophobic and superoleophobic materials, slippery liquid-infused porous surfaces, etc. Full article

Anodized aluminum oxide (AAO) molds were used for the production of large-area and inexpensive superhydrophobic polymer films. A controlled anodization methodology was developed for the fabrication of hierarchical micro–nanoporous (HMN) AAO imprint molds (HMN-AAO), where phosphoric acid was used as both an electrolyte and a widening agent. Heat generated upon repetitive high-voltage (195 V) anodization steps is effectively dissipated by establishing a cooling channel. On the HMN-AAO, within the hemispherical micropores, arrays of hexagonal nanopores are formed. The diameter and depth of the micro- and nanopores are 18/8 and 0.3/1.25 µm, respectively. The gradual removal of micropatterns during etching in both the vertical and horizontal directions is crucial for fabricating HMN-AAO with a high aspect ratio. HMN-AAO rendered polycarbonate (PC) and polymethyl methacrylate (PMMA) films with respective water contact angles (WCAs) of 153° and 151°, respectively. The increase in the WCA is 80% for PC (85°) and 89% for PMMA (80°). On the PC and PMMA films, mechanically robust arrays of nanopillars are observed within the hemispherical micropillars. The micro–nanopillars on these polymer films are mechanically robust and durable. Regular nanoporous AAO molds resulted in only a hydrophobic polymer film (WCA = 113–118°). Collectively, the phosphoric acid-based controlled anodization strategy can be effectively utilized for the manufacturing of HMN-AAO molds and roll-to-roll production of durable superhydrophobic surfaces. Full article