Bioinspired one step hydrothermal fabricated superhydrophobic aluminum alloy with favorable corrosion resistance

Leaf on a Film: Mesoporous Silica-Based Epoxy Composites with Superhydrophobic Biomimetic Surface Structure as Anti-Corrosion and Anti-Biofilm Coatings

In this study, a series of amine-modified mesoporous silica (AMS)-based epoxy composites with superhydrophobic biomimetic structure surface of Xanthosoma sagittifolium leaves (XSLs) were prepared and applied as anti-corrosion and anti-biofilm coatings. Initially, the AMS was synthesized by the base-catalyzed sol-gel reaction of tetraethoxysilane (TEOS) and triethoxysilane (APTES) through a non-surfactant templating route. Subsequently, a series of AMS-based epoxy composites were prepared by performing the ring-opening polymerization of DGEBA with T-403 in the presence of AMS spheres, followed by characterization through FTIR, TEM, and CA. Furthermore, a nano-casting technique with polydimethylsiloxane (PDMS) as the soft template was utilized to transfer the surface pattern of natural XSLs to AMS-based epoxy composites, leading to the formation of AMS-based epoxy composites with biomimetic structure. From a hydrophilic CA of 69°, the surface of non-biomimetic epoxy significantly increased to 152° upon introducing XSL surface structure to the AMS-based epoxy composites. Based on the standard electrochemical anti-corrosion and anti-biofilm measurements, the superhydrophobic BEAMS3 composite was found to exhibit a remarkable anti-corrosion efficiency of ~99% and antimicrobial efficacy of 82% as compared to that of hydrophilic epoxy coatings.

Advances in superhydrophobic material research: from preparation to electrified railway protection

Freezing is a serious problem that affects the power, transport, and transmission industries and is a major concern for the national economy and safety. Currently, several engineering de-icing methods, such as thermal, mechanical, and chemical de-icing, have shown problems related to energy consumption, efficiency, and the environment. Superhydrophobic materials have high droplet contact and roll angles, which can reduce the droplet residence and ice adhesion on their surfaces and have unique advantages in the self-cleaning and anti-icing fields. This paper introduces the development of infiltration theory and superhydrophobic materials and their principles of anti-icing and de-icing. Herein, the preparation and coating methods of superhydrophobic materials in applications are summarised, the performance and lifetime issues of superhydrophobic materials in applications are clarified, and the research progress on superhydrophobic materials in different fields is reviewed. Prospects for the application of superhydrophobic materials in electrified railways are also presented. A feasibility study was conducted to solve some of the existing problems of electrified railways, providing a theoretical basis for the development of electrified railways.

Durability and corrosion behaviors of superhydrophobic amorphous coatings: a contrastive investigation

Superhydrophobic surfaces can be derived from roughening hydrophobic materials. However, the superhydrophobic surfaces with various micro/nano morphologies present variations of chemical and mechanical durability, which limits their practical applications. Very little actually is known about comparing durability and corrosion resistance of concave and convex superhydrophobic surface structures systematically. In this paper, two kinds of superhydrophobic AlNiTi amorphous coatings with concave and convex surfaces were obtained by chemical etching and hydrothermal methods, respectively. Benefiting from nanoscale sheet structure, the convex superhydrophobic coating displays higher water-repellence (contact angle = 157.6°), better self-cleaning performance and corrosion resistance. The corrosion current density of the convex superhydrophobic surface is approximately one order of magnitude smaller than the concave superhydrophobic surface. Besides, the long-term chemical stability and mechanical durability of both superhydrophobic surfaces were also investigated. The formation and damage mechanisms of these two kinds of superhydrophobic surfaces were proposed. It is hoped that these investigations could provide clear guidance for the real-world applications of superhydrophobic amorphous coatings.

Heat Stability and Icing Delay on Superhydrophobic Coatings in Facile One Step

Superhydrophobic coatings are limited to poor durability and a tedious preparation process. In this work, an efficient, eco-friendly, and cost-effective sol-gel method is developed for preparing superhydrophobic surfaces using an all-in-one suspension composed of methyltrimethoxysilane (MTMS), nano silicon dioxide (SiO₂) particles, and micron zinc oxide (ZnO) particles. Superhydrophobic coatings with a contact angle (CA) up to 153.9° and a sliding angle (SA) of about 3.0° are prepared on Q235 steel substrates using MTMS 5 mL, 0.8 g of nano SiO₂, and 0.2 g of micron ZnO. The morphology of the superhydrophobic coating is characterized by scanning electron microscopy (SEM), and the surface is covered with a micro- and nano-scaled hierarchical rough structure. A series of tests are conducted, including long-term stability tests and thermostability tests. The CAs are all above 150°, and the SAs are below 6.3°, indicating the excellent static stability of the prepared superhydrophobic coatings. Moreover, the CA of the superhydrophobic coating remains above 152° after 120 h of UV exposure, and the time for a water droplet to freeze on the surface of the superhydrophobic coating is 18 times of the bare Q235 steel, indicating that the superhydrophobic coating exhibits good resistance to UV radiation and icing-delay properties.

Fabrication and Characterization of Superhydrophobic Al-Based Surface Used for Finned-Tube Heat Exchangers

Enhancing the heat transfer performance of heat exchangers is one of the main methods to reduce energy consumption and carbon emissions in heating, ventilation, air-conditioning and refrigeration (HVAC&R) systems. Wettability modified surfaces developed gradually may help. This study aims to improve the performance of heat exchangers from the perspective of component materials. The facile and cost-effective fabrication method of superhydrophobic Al-based finned-tube heat exchangers with acid etching and stearic acid self-assembly was proposed and optimized in this study, so that the modified Al fins could achieve stronger wettability and durability. The effect of process parameters on the wettability of the Al fins was by response surface methodology (RSM) and variance analysis. Then, the modified fins were characterized by field-emission scanning electron microscopy (FE-SEM), 3D topography profiler, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), respectively. The durability of the superhydrophobic fins was investigated by air exposure, corrosion resistance, and mechanical robustness experiments. The RSM and variance analysis demonstrated that a water contact angle (WCA) of 166.9° can be obtained with the etching time in 2 mol/L HCl solution of 10.5 min, the self-assembly time in the stearic acid ethanol solution of 48 h, and drying under 73.0 °C. The surface morphology showed suitable micro-nano structures with a mean roughness (Ra) of 467.58 nm and a maximum peak-to-valley vertical distance (Rt) of 4.095 μm. The chemical component demonstrated the self-assembly of an alkyl chain. The WCAs declined slightly in durability experiments, which showed the feasibility of the superhydrophobic heat exchangers under actual conditions.

Superhydrophobic Self-Assembled Silane Monolayers on Hierarchical 6082 Aluminum Alloy for Anti-Corrosion Applications

In this work, a two-stage methodology to design super-hydrophobic surfaces was proposed. The first step consists of creating a rough nano/micro-structure and the second step consists of reducing the surface energy using octadecyltrimethoxysilane. The surface roughening was realized by three different short-term pretreatments: (i) Boiling water, (ii) HNO3/HCl etching, or (iii) HF/HCl etching. Then, the surface energy was reduced by dip-coating in diluted solution of octadecyltrimethoxysilane to allow the formation of self-assembled silane monolayers on a 6082-T6 aluminum alloy surface. Super-hydrophobic aluminum surfaces were investigated by SEM-EDS, FTIR, profilometry, and contact and sliding angles measurements. The resulting surface morphologies by the three approaches were structured by a dual hierarchical nano/micro-roughness. The surface wettability varied with the applied roughening pretreatment. In particular, an extremely high water contact angle (around 180°) and low sliding angle (0°) were evidenced for the HF/HCl-etched silanized surface. The results of electrochemical tests demonstrate a remarkable enhancement of the aluminum alloy corrosion resistance through the proposed superhydrophobic surface modifications. Thus, the obtained results evidenced that the anti-wetting behavior of the aluminum surface can be optimized by coupling an appropriate roughening pretreatment with a self-assembled silane monolayer deposition (to reduce surface energy) for anticorrosion application.