For superhydrophobic surfaces immersed in water, a thin layer of air could be entrapped in the solid/liquid interface. This air may hinder the diffusion of dissolved corrosive species (such as Cl- ions in water) to the metallic substrate and, consequently, protect the metal from corrosion. However, in the dynamic water, the relative motion between the solid and the liquid would labilize the entrapped air and, consequently, decrease the corrosion resistance. In this work, to clarify the role of water flow velocity in such corrosion behavior, a superhydrophobic surface on aluminum substrates coded as Al-HCl-H2O-BT-SA was prepared by sequential treatment with HCl, boiling water, bis-(γ-triethoxysilylpropyl)-tetrasulfide (KH-Si69, BT) and stearic acid (SA). The contrast samples coded as Al-HCl-BT-SA, Al-HCl-H2O-SA, and Al-HCl-SA were also prepared similarly by omitting the treatment in boiling-water, the BT passivation, and the treatment in boiling-water/passivation by BT, respectively. These samples were then immersed into an aqueous solution of NaCl with different flow velocity (0, 0.5, 1.0, 1.5, and 2.0 m s-1), and its dynamic corrosion behavior was investigated. The results showed that, as the flow velocity increased, the corrosion resistance of the Al-HCl-H2O-BT-SA sample indeed deteriorated. However, compared with the contrast samples of Al-HCl-BT-SA, Al-HCl-H2O-SA, and Al-HCl-SA, the deterioration in corrosion resistance for the Al-HCl-H2O-BT-SA sample was much lower, implying that the dynamic corrosion resistance of the superhydrophobic surfaces was closely related with the micro-structures and the organic passivated layers. The present study therefore provided a fundamental understanding for the applications of superhydrophobic samples to prevent the corrosion, especially, for various vessels in dynamic water.
It is generally recognized that superhydrophobic surfaces in water may be used for corrosion resistance due to the entrapped air in the solid/liquid interface and could find potential applications in the protection of ship hull. For a superhydrophobic surface, as its immersion depth into water increases, the resultant hydrostatic pressure is also increased, and the entrapped air can be squeezed out much more easily. It is therefore predicted that high hydrostatic pressure would cause an unexpected decrease in corrosion resistance for the vessels in deep water (e.g., submarines) because of the unstable entrapped air. In this work, in order to clarify the role of hydrostatic pressure in the corrosion behavior of superhydrophobic surfaces, two typical superhydrophobic surfaces (SHSs) were prepared on bare and oxidized aluminum substrates, respectively, and then were immersed into the NaCl aqueous solutions with different depths of ∼0 cm (hydrostatic pressure ∼0 kPa), 10 cm (1 kPa), and 150 cm (15 kPa). It was found out for the SHSs on the oxidized Al, as the hydrostatic pressure increased, the corrosion behavior became severe. However, for the SHSs on the bare Al, their corrosion behavior was complex due to hydrostatic pressure. It was found that the corrosion resistance under 1 kPa was the highest. Further mechanism analysis revealed that this alleviated corrosion behavior under 1 kPa resulted from suppressing the oxygen diffusion through the liquid and reducing the subsequent corrosion rate as compared with 0 kPa, whereas the relatively low hydrostatic pressure (HP) could stabilize the entrapped air and hence enhance the corrosion resistance, compared with 15 kPa. The present study therefore provided a fundamental understanding for the applications of SHSs to prevent the corrosion, especially for various vessels in deep water.
In recent years, inspired by “biomimicry”, superhydrophobic surfaces have gained significant attention. Superhydrophobic surfaces demonstrate notable advantages in addressing interfacial issues, and superhydrophobic coatings exhibit excellent waterproofness, anti-fouling, self-cleaning, anti-corrosion, and additional capabilities, making them promising next-generation waterproof materials. However, the complex preparation process, coupled with poor wear resistance and environmental durability, severely limits their practical applications. Therefore, this article started from simplifying the preparation process and improving the durability of the coatings. Epoxy resin (E51) was used as the film-forming material, and carbon nanotubes (CNTs) and dual-sized SiC particles (nano-SiC and micro-SiC) were used as the fillers. Room temperature vulcanized silicone rubber (RTV) was used as a binder interacting with epoxy resin to promote the interface interaction between the fillers and the polymers. This process resulted in the successful preparation of superhydrophobic coatings with outstanding comprehensive performance. When the ratio of μ-SiC to n-SiC was 1:1, the prepared coating exhibited the best superhydrophobic properties with a water contact angle (WCA) of 167.4° and a sliding angle (SA) of 4.6°. Even after undergoing severe mechanical tests, such as sandpaper abrasion for 1000 cycles, sand impact for 100 cycles, cross-cut test, and tape-peeling for 70 cycles, the coatings still maintained their non-wetting Cassie-Baxter state. Furthermore, even after immersion in strong acid, strong alkali and 3.5 wt% NaCl solutions for 6 days, keeping at 500 ℃ for 2 hours, and exposure to ultraviolet for 6 days, the coatings still exhibited excellent superhydrophobicity. This suggested that the prepared coating had excellent chemical stability and high-temperature resistance. In addition, the superhydrophobic coating exhibited exceptional capabilities in self-cleaning, anti-corrosion, anti-icing, and de-icing properties. Furthermore, this coating, applicable to diverse substrates including board, steel, paper, and glass, demonstrated an impressive water contact angle (WCA) and sliding angle (SA). The spraying method offers the benefits of simplicity and cost-effectiveness. This is poised to significantly broaden its practical applications in various fields, including construction, transportation, and the chemical industry.
Solar energy-based renewable energy conversion and storage technologies offer a great promise of combating energy shortage and transitioning to a sustainable society. Efficient collection and transformation play decisive roles in optimizing the harvest of solar energy. Photothermal conversion has emerged as the most efficient solar energy conversion technology, particularly, photothermal coatings could convert light into heat and has triggered a surge of interest in ice removal related applications. Here, we present a comprehensive review of popular documented photothermal conversion materials and the mechanisms of photothermal conversion technologies. Additionally, we pay attention to efficient light-trapping structures for outperformed solar-driven photothermal materials. After that, we investigate the mechanisms of the deicing process. Finally, we discuss the progress of photothermal deicing systems and summarize future challenges in improving their performance. This review serves as a reasonable reference for the classification of photothermal materials and the construction of light-trapping structures, providing valuable insight into the design of photothermal materials for anti-icing applications.
Abstract Superhydrophobic surfaces with an excellent anti-icing performance were prepared on an aluminum substrate using a simple one-step spin coating method. The wettability, morphology, and surface compositions of the prepared surfaces were characterized using the measuring instrument for contact angle and sliding angle, scanning electron microscopy, and Fourier transform infrared spectroscopy, respectively. The contact angle of the as-prepared superhydrophobic surfaces was as high as 165 ± 1.5°, and the sliding angle was less than 5° for a 4 μL pure water droplet, indicating excellent superhydrophobicity and low adhesion. The effects of addition of ZnO powders in different amounts on the morphology and wettability were further analyzed. Moreover, the anti-icing performance of the superhydrophobic surfaces was investigated using a simple lab-made icing monitoring apparatus, and the results are discussed using the one dimensional heat transfer and classical nucleation theory. It was found that the theoretical icing time of the superhydrophobic sample was about five times longer than that of the reference sample whereas for the untreated aluminum, the contact angle was 72 ± 1.5°, which was nearly consistent with the experimental results. The present study demonstrates that the prepared superhydrophobic surface can delay the icing time and decrease the icing temperature, and could be found potential applications in various industries.
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