Design of mechanical robust superhydrophobic Cu coatings with excellent corrosion resistance and self-cleaning performance inspired by lotus leaf

Anisotropic Superhydrophobic Properties Replicated from Leek Leaves

A bio-inspired approach to fabricate robust superhydrophobic (SHB) surfaces with anisotropic properties replicated from a leek leaf is presented. The polydimethylsiloxane (PDMS) replica surfaces exhibit anisotropic wetting, anti-icing, and light scattering properties due to microgrooves replicated from leek leaves. Superhydrophobicity is achieved by a novel modified candle soot (CS) coating that mimics leek's epicuticular wax. The resulting surfaces show a contact angle (CA) difference of ≈30° in the directions perpendicular and parallel to the grooves, which is similar to the anisotropic properties of the original leek leaf. The coated replica is durable, withstanding cyclic bending tests (up to 10 000 cycles) and mechanical sand abrasion (up to 60 g of sand). The coated replica shows low ice adhesion (10 kPa) after the first cycle; and then, increases to ≈70 kPa after ten icing-shearing cycles; while, anisotropy in ice adhesion becomes more evident with more cycles. In addition, the candle soot-coated positive replica (CS-coated PR) demonstrates a transmittance of ≈73% and a haze of ≈65% at the wavelength of 550 nm. The results show that the properties depend on the replicated surface features of the leek leaf, which means that the leek leaf appears to be a highly useful template for bioinspired surfaces.

Ultrathin Water-Responsive Zwitterionic Hydrogel Brush Coatings for Long-Term Corrosion Protection

Preventing metal corrosion has usually been associated with water-repellent coatings that inhibit the penetration of aggressive chloride ions. Contrary to this conventional wisdom, we engineered ultrathin superhydrophilic zwitterionic hydrogel brushes rooted in a nanoporous anodic aluminum oxide (AAO) substrate that effectively hampered the adsorption of hydrated chloride ions (Cl-·H2O) on the Al alloy surface. The hydrogel brush coating enhanced corrosion resistance by 3 orders of magnitude, with corrosion current density declining from 1.518 to 1.567 × 10-3 μA cm-2. Despite suffering from long-term salt-spaying tests, zwitterionic hydrogel brush coating retained 2 orders of magnitude of corrosion resistance. Direct Raman spectroscopic evidence manifested that interfacial water comprised both highly ordered hydrogen-bonded water and disordered water containing hydrated Cl- ions. Under the hydration effect of zwitterionic hydrogel brushes, an interfacial disordered water structure dynamically transformed into a hydrogen-bonded water film. We correlated the structure and quantities of interfacial water with the corrosion current density and chloride adsorption. Hydrogen-bonded water improved by zwitterionic hydrogel brushes weakened the affinity and adsorption of hydrated Cl- ion water on the oxide film, resulting in excellent corrosion protection. Therefore, employing localized hydration tuning strategies, these findings are anticipated to generally empower ordered interfacial water to enhance metal corrosion resistance through precise interfacial engineering.

Preparation of a Stable Superhydrophobic Mortar Surface Using a One-Step Method

Research efforts have intensified on developing superhydrophobic surfaces on concrete structures to limit the damage caused by the natural porosity and hydrophilicity of cementitious materials. However, the feasibility idea is impeded by the complex preparation process and weak adhesion/stability performance. Therefore, superhydrophobic coatings were rapidly prepared on mortar surfaces by a straightforward and effective one-step method using zinc oxide (ZnO) modified with stearic acid and epoxy resin. The microstructure, physical/chemical properties, hydrophobic properties, and stability of the coatings were systematically investigated. The experimental results showed that the water contact angle of the samples reached a maximum value of 164.2° and a sliding angle of 4.6° when the stearic acid content was 0.5 g. The water absorption of the coated superhydrophobic mortar was reduced by approximately 61% compared to that of ordinary mortar, and neither particulate pollutants nor liquid pollutants could contaminate the superhydrophobic mortar. The coating maintained a superhydrophobic state and exhibited good physical durability after sandpaper abrasion, tape peeling, and high-temperature resistance tests. The water cluster diffusion coefficient on surface of the ordinary coating was 0.1645 × 10-4 and 0.0328 × 10-4 cm2/s on surface of the modified coating after molecular dynamics simulation.

Up to Date Review of Nature-Inspired Superhydrophobic Textiles: Fabrication and Applications

In recent years, with the rapid development of the economy and great progress in science and technology, people have become increasingly concerned about their quality of life and physical health. In order to pursue a higher life, various functional and biomimetic textiles have emerged one after another and have been sought after by people. There are many animal and plant surfaces with special wettability in nature, and their unique "micro-nano structures" and low surface energy have attracted extensive attention from researchers. Researchers have prepared various textiles with superhydrophobic features by mimicking these unique structures. This review introduces the typical organisms with superhydrophobicity in nature, using lotus, water strider, and cicada as examples, and describes their morphological features and excellent superhydrophobicity. The theoretical model, commonly used raw materials, and modification technology of superhydrophobic surfaces are analyzed. In addition, the application areas and the current study status of superhydrophobic surfaces for textiles are also summarized. Finally, the development prospects for superhydrophobic textiles based on bionic technology are discussed.

A Simple and Convenient Method for Preparing Fluorine-Free Durable Superhydrophobic Coatings Suitable for Multiple Substrates

Superhydrophobic coatings have attracted a lot of attention due to their excellent self-cleaning and anti-fouling capabilities. However, the preparation processes for several superhydrophobic coatings are intricate and expensive, which restricts their usefulness. In this work, we present a straightforward technique for creating durable superhydrophobic coatings that can be applied to a variety of substrates. The addition of C9 petroleum resin to a styrene-butadiene-styrene (SBS) solution lengthens the SBS backbone and undergoes a cross-linking reaction to form a dense spatial cross-linked structure, improving the storage stability, viscosity, and aging resistance of the SBS. The combined solution functions as a more stable and effective adhesive. Using a two-step spraying technique, the hydrophobic silica (SiO₂) nanoparticles solution was applied to the surface to create durable nano-superhydrophobic coatings. Additionally, the coatings have excellent mechanical, chemical, and self-cleaning stability. Furthermore, the coatings have wide application prospects in the fields of water-oil separation and corrosion prevention.

Recent Advances on the Abrasion Resistance Enhancements and Applications of Superhydrophobic Materials

Researches on superhydrophobicity have been overwhelming and have shown great advantages in various fields. However, the abrasion resistance of superhydrophobic structures was usually poor, and they were easily damaged by external force or harsh environment, which greatly limited the applications of superhydrophobic surfaces. Much attention has been paid to improving the abrasion resistance of superhydrophobic materials by researchers. In this review, aimed at the advances on improving the abrasion resistance of superhydrophobic surfaces, it was summarized and compared three enhancement strategies including the reasonably design of micro-nano structures, the adoption of adhesives, and the preparation of self-healing surface. Finally, the applications of typical superhydrophobic materials with abrasion resistance were reviewed in various fields. In order to broaden the application fields of superhydrophobic materials, the abarasion resistance should be further improved. Therefore, we proposed the ideas for the future development of superhydrophobic materials with higher abrasion resistance. We hope that this review will provide a new approach to the preparation and development of stable superhydrophobic surfaces with higher abrasion resistance.

Wettability, Self-Cleaning Property, and Mechanical Durability of A390 Aluminum Alloy with the Major Effect of Si Phases

Si phases with specific shapes, including primary and eutectic Si phases, were etched on the surface of A390 Al alloy by chemical etching. Meanwhile, their effects on the wettability, self-cleaning properties, and mechanical durability of etched A390 aluminum alloy surfaces were investigated. The results showed that the surface etched for 5 min and modified by 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS-17) demonstrated a contact angle of 153.2 ± 1.4° and a sliding angle of 11.2 ± 1.6°. The theoretical contact angle calculated by constructing a wetting model of Si phases approximates the actual contact angle. Further experiments indicated that the etched surface acquired excellent self-cleaning properties. In addition, the exposed Si phases formed a strong support skeleton, which greatly improved the wear resistance of the hydrophobic surface.

Fundamentals and utilization of solid/ liquid phase boundary interactions on functional surfaces

The affinity of macroscopic solid surfaces or dispersed nano- and bioparticles towards liquids plays a key role in many areas from fluid transport to interactions of the cells with phase boundaries. Forces between solid interfaces in water become especially important when the surface texture or particles are in the colloidal size range. Although, solid-liquid interactions are still prioritized subjects of materials science and therefore are extensively studied, the related literature still lacks in conclusive approaches, which involve as much information on fundamental aspects as on recent experimental findings related to influencing the wetting and other wetting-related properties and applications of different surfaces. The aim of this review is to fill this gap by shedding light on the mechanism-of-action and design principles of different, state-of-the-art functional macroscopic surfaces, ranging from self-cleaning, photoreactive or antimicrobial coatings to emulsion separation membranes, as these surfaces are gaining distinguished attention during the ongoing global environmental and epidemic crises. As there are increasing numbers of examples for stimulus-responsive surfaces and their interactions with liquids in the literature, as well, this overview also covers different external stimulus-responsive systems, regarding their mechanistic principles and application possibilities.