Self-Healable Superomniphobic Surfaces for Corrosion Protection

Self-Healing Superwetting Surfaces, Their Fabrications, and Properties

The research on superwetting surfaces with a self-healing function against various damages has progressed rapidly in the recent decade. They are expected to be an effective approach to increasing the durability and application robustness of superwetting materials. Various methods and material systems have been developed to prepare self-healing superwetting surfaces, some of which mimic natural superwetting surfaces. However, they still face challenges, such as being workable only for specific damages, external stimulation to trigger the healing process, and poor self-healing ability in the water, marine, or biological systems. There is a lack of fundamental understanding as well. This article comprehensively reviews self-healing superwetting surfaces, including their fabrication strategies, essential rules for materials design, and self-healing properties. Self-healing triggered by different external stimuli is summarized. The potential applications of self-healing superwetting surfaces are highlighted. This article consists of four main sections: (1) the functional surfaces with various superwetting properties, (2) natural self-healing superwetting surfaces (i.e., plants, insects, and creatures) and their healing mechanism, (3) recent research development in various self-healing superwetting surfaces, their preparation, wetting properties in the air or liquid media, and healing mechanism, and (4) the prospects including existing challenges, our views and potential solutions to the challenges, and future research directions.

Near-Infrared Responsive Smart Superhydrophobic Coating with Self-Healing and Robustness Enhanced by Disulfide-Bonded Polyurethane

Synergistic self-healing materials and inorganic particles to create self-healing superhydrophobic surfaces for improving their robustness is a common technique, but the suitability between the two is rarely mentioned. In this work, we developed a multifunctional superhydrophobic coating with room-temperature stability, mechanical stability, self-healing, and NIR stimuli response, in which self-healing polyurethane (PU) serves as the interface reinforcement layer and poly(dopamine) (PDA)-coated flower-like ZnO composite particles serve as the hydrophobic layer. A series of temperature-dependent self-healing PU materials were designed and synthesized by regulating the ratio of hard and soft chain segments in PU, and the relationship between the healing temperature of PU and the hydrophobic stability of the composite coatings was investigated. Based on dynamic hydrogen and disulfide bonds, PUs displayed excellent self-healing performance. Thanks to the self-healing and interfacial strengthening effect of PU and the photothermal properties of PDA, the composite coating exhibits not only excellent mechanical stability but also rapid self-healing ability in response to NIR stimuli. Furthermore, the smart coating demonstrated superior self-cleaning and corrosion resistance. This work provides a reference for developing strong and stable water-repellent reversible superhydrophobic coatings with great potential and promising future.

Nanofiber Composite Coating with Self-Healing and Active Anticorrosive Performances

Synergetic self-healing anticorrosion behaviors, by forming a self-assembly protective layer and repairing coating passive barrier, exhibit great potential in handling the notorious metal corrosion phenomenon. Herein, we developed a nanofiber-supported anticorrosion coating with synergistic protection effects of both self-healing and active corrosion inhibition, via a facile electrospinning combined coating technique. Polycaprolactone (PCL) nanofiber integrated with 2-mecapobenzothiazole-loaded halloysite nanotubes (HNTs-MBT) is directly deposited on the surface of metal substrate, forming an interconnected fiber network framework. The encapsulated corrosion inhibitor MBT can be released by a pH-triggered manner to realize instant corrosion protections. Additionally, coating defects could be repeatedly repaired by continuous polymer fiber upon heat treatment and the anticorrosion efficiency effectively remained, even after three cycles of damage-healing. Moreover, the repaired coating also exhibited durable anticorrosion performance, mainly attributed to the synergetic effects of both thermal-triggered bulk healing and active corrosion inhibition. This type of dual-functional coating provides efficient anticorrosive performances and may show great promise in long-term corrosion protection.

Design of Icephobic Surfaces by Lowering Ice Adhesion Strength: A Mini Review

Ice accretion can lead to severe consequences in daily life and sometimes catastrophic events. To mitigate the hazard of icing, passive icephobic surfaces have drawn widespread attentions because of their abilities in repelling incoming water droplets, suppressing ice nucleation and/or lowering ice adhesion strength. As time elapses and temperature lowers sufficiently, ice accretion becomes inevitable, and a realistic roadmap to surface icephobicity for various outdoor anti-icing applications is to live with ice but with the lowest ice adhesion strength. In this review, surfaces with icephobicity are critically categorized into smooth surfaces, textured surfaces, slippery surfaces and sub-surface textured surfaces, and discussed in terms of theoretical limit, current status and perspectives. Particular attention is paid to multiple passive anti-icing strategies combined approaches as proposed on the basis of icephobic surfaces. Correlating the current strategies with one another will promote understanding of the key parameters in lowering ice adhesion strength. Finally, we provide remarks on the rational design of state-of-the-art icephobic surfaces with low ice adhesion strength.

Water-Responsive Self-Repairing Superomniphobic Surfaces via Regeneration of Hierarchical Topography

Superomniphobic surfaces that can self-repair physical damage are desirable for sustainable performance over time in many practical applications that include self-cleaning, corrosion resistance, and protective gears. However, fabricating such self-repairing superomniphobic surfaces has thus far been a challenge because it necessitates the regeneration of both low-surface-energy materials and hierarchical topography. Herein, a water-responsive self-repairing superomniphobic film is reported by utilizing cross-linked hydroxypropyl cellulose (HPC) composited with silica (SiO₂) nanoparticles (HPC-SiO₂) that is treated with a low-surface-energy perfluorosilane. The film can repair physical damage (e.g., a scratch) in approximately 10 s by regenerating its hierarchical topography and low-surface-energy material upon the application of water vapor. The repaired region shows an almost complete recovery of its inherent superomniphobic wettability and mechanical hardness. The repairing process is driven by the reversible hydrogen bond between the hydroxyl (-OH) groups which can be dissociated upon exposure to water vapor. This results in a viscous flow of the HPC-SiO₂ film into the damaged region. A mathematical model composed of viscosity and surface tension of the HPC-SiO₂ film can describe the experimentally measured viscous flow with reasonable accuracy. Finally, we demonstrate that the superomniphobic HPC-SiO₂ film can repair physical damage by a water droplet pinned on a damaged area or by sequential rolling water droplets.

Preparation of the Temperature-Responsive Superhydrophobic Paper with High Stability

In this paper, a method for preparing a high-stability superhydrophobic paper with temperature-induced wettability transition is proposed. First, a temperature-responsive superhydrophobic triblock polymer PHFMA-PTSPM-PNIPAAm was prepared by one-step polymerization of TSPM, HFMA, and NIPAAm in a mass ratio of 0.3:0.3:0.3, then a superhydrophobic paper with a good temperature response was successfully prepared by grafting amino-modified SiO₂ with the polymer to modify the surface of the paper. A further study found that when the mass ratio of amino-modified SiO₂ to polymer is 0.2, the coating has good superhydrophobicity and transparency. What is more, the prepared modified paper is in a superhydrophobic state when the temperature is higher than 32 °C, and is in a superhydrophilic state when it is lower than 32 °C, which can realize free conversion between superhydrophobic and superhydrophilic states. In addition, the superhydrophobic paper prepared by this method not only has high oil-water separation efficiency, and the superhydrophobic coating shows good stability and transparency, but also has low requirements of environmental conditions for preparation, relatively simple preparation process, and strong repeatability, and it has a very broad application prospect.

Engineered Nanoparticles with Decoupled Photocatalysis and Wettability for Membrane-Based Desalination and Separation of Oil-Saline Water Mixtures

Membrane-based separation technologies are the cornerstone of remediating unconventional water sources, including brackish and industrial or municipal wastewater, as they are relatively energy-efficient and versatile. However, membrane fouling by dissolved and suspended substances in the feed stream remains a primary challenge that currently prevents these membranes from being used in real practices. Thus, we directly address this challenge by applying a superhydrophilic and oleophobic coating to a commercial membrane surface which can be utilized to separate and desalinate an oil and saline water mixture, in addition to photocatalytically degrading the organic substances. We fabricated the photocatalytic membrane by coating a commercial membrane with an ultraviolet (UV) light-curable adhesive. Then, we sprayed it with a mixture of photocatalytic nitrogen-doped titania (N-TiO₂) and perfluoro silane-grafted silica (F-SiO₂) nanoparticles. The membrane was placed under a UV light, which resulted in a chemically heterogeneous surface with intercalating high and low surface energy regions (i.e., N-TiO₂ and F-SiO₂, respectively) that were securely bound to the commercial membrane surface. We demonstrated that the coated membrane could be utilized for continuous separation and desalination of an oil–saline water mixture and for simultaneous photocatalytic degradation of the organic substances adsorbed on the membrane surface upon visible light irradiation.

Large-scale fabrication of a durable and self-healing super-hydrophobic coating with high thermal stability and long-term corrosion resistance

Durability is a crucial feature to expand the application field of artificial superhydrophobic coatings. Herein, a kind of durable superhydrophobic coating is prepared by a simple and cheap method using a fluorine-free suspension as the raw material, which consists of epoxy modified silicone resin (MSR), functionalized SiO2, GO, and lamellar mica powder (MP). The MSR@SiO2 + GO + MP coating shows outstanding surface wettability with a water contact angle of 163.8°, a low sliding angle of 3.5° and the microdroplet adhesive force of about 12.6 ± 0.5 μN. Furthermore, it can withstand alternating high and low temperatures, intense UV radiation for 7 days, strong chemical attack, and various mechanical durability tests. In addition, the coating also exhibits a significantly repairable ability to resist O2 plasma etching, and outstanding self-cleaning both in air and oil even after mechanical damage. The mechanism for the influence of the multiple hybridizations on the long-term corrosion stability and thermal-related properties of the superhydrophobic coating is further systematically studied. The simple method and superhydrophobic coating should have good application prospects in large area protection.

Superwetting interfaces for oil/water separation

Superhydrophobic coatings have been applied in various fields. The materials used in the preparation of superhydrophobic coatings have attracted the attention of scholars. Due to the harm of fluorine-containing substances with low surface energy to the environment, fluorine-free superhydrophobic coatings have become a hotspot in the research field. Herein, a fluorine-free superhydrophobic coating with oil/water separation was made by a solution immersion way. The fluorine-free copolymer and polydimethylsiloxane (PDMS)/SiO2 nanoparticles (NPs) were mixed to prepare a composite solution, and the superhydrophobic surface was obtained on the paper by a dipping method. The scanning electron microscope, x-ray photoelectron spectrometer, 1H nuclear magnetic resonance, and Fourier transform infrared were used to study the surface characteristics and structural composition of the superhydrophobic material. The research proved that the copolymer and PDMS/SiO2 NPs were successfully coated on the paper surface, and the rough structure of the superhydrophobic surface was also attributed to the introduction of the copolymer and PDMS/SiO2 NPs. The evaluation of the coating has proved its excellent hydrophobicity, oil/water separation performance, and self-cleaning performance. The coating is a sustainable and environmentally friendly superhydrophobic material that can be used in packaging, construction, petrochemical, and other industries.

Thermally Sensitized Membranes for Crude Oil-Water Remediation under Visible Light

Effective remediation of produced water requires separating crude oil-water mixture and removing the dissolved organic pollutants. Membranes with selective wettability for water over oil enable the gravity-driven separation of an oil-water mixture by allowing water to permeate through while repelling oil. However, these membranes are often limited by their inability to remove the dissolved organic pollutants. In this work, a membrane with in-air superhydrophilic and underwater superoleophobic wettability is fabricated by thermal annealing of a stainless steel mesh. The resulting membrane possesses a hierarchical surface texture covered with a photocatalytic oxide layer composed of iron oxide and chromium oxide. The membrane exhibits chemical and mechanical robustness, which makes it suitable for remediation of crude oil and water mixture. Further, after being fouled by crude oil, the membrane can recover its inherent water-rich permeate flux upon visible light irradiation. Finally, the membrane demonstrates that it can separate surfactant-stabilized crude oil-in-water emulsion under gravity and decontaminate water-rich permeate by photocatalytic degradation of dissolved organic pollutants upon continuous irradiation of visible light.

Selective Wettability Membrane for Continuous Oil-Water Separation and In Situ Visible Light-Driven Photocatalytic Purification of Water

Membrane-based technologies are attractive for remediating oily wastewater because they are relatively energy-efficient and are applicable to a wide range of industrial effluents. For complete treatment of oily wastewater, removing dissolved contaminants from the water phase is typically followed by adsorption onto an adsorbent, which complicates the process. Here, an in-air superhydrophilic and underwater superoleophobic membrane-based continuous separation of surfactant-stabilized oil-in-water emulsions and in situ decontamination of water by visible-light-driven photocatalytic degradation of dissolved organic contaminants is reported. The membrane is fabricated by utilizing a thermally sensitized stainless steel mesh coated with visible light absorbing iron-doped titania nanoparticles. Post annealing of the membrane can enhance the adhesion of nanoparticles to the membrane surface by formation of a bridge between them. An apparatus that enables continuous separation of surfactant-stabilized oil-in-water emulsion and in situ photocatalytic degradation of dissolved organic matter in the water-rich permeate upon irradiation of visible light on the membrane surface with greater than 99% photocatalytic degradation is developed. The membrane demonstrates the recovery of its intrinsic water-rich permeate flux upon continuous irradiation of light after being contaminated with oil. Finally, continuous oil-water separation and in situ water decontamination is demonstrated by photocatalytically degrading model toxins in water-rich permeate.

Robust, transparent, superhydrophobic coatings using novel hydrophobic/hydrophilic dual-sized silica particles

HYPOTHESIS

The superhydrophobic lotus leaf has dual-scale surface structures, that is, nano-bumps on micro-mountains. Large hydrophilic particles, due to its high surface energy and weight, have high affility to substrates and tend to precipitate at the bottom of coating films. Small hydrophobic particles, due to its low surface energy and weight, tends to sit on the top of coating films and form porous structures. To mimic the lotus leaf surface, it may be possible to develop dual-sized particle films, in which small particles are decorated on large particles.

EXPERIMENTS

A one-step spin coating of a mixture of dual-sized silica particles (55/200 nm) was used. Epoxy resin was added to improve the adhesion of particle films. The single-sized and dual-sized particle films were compared. The mechanical robustness of particle films was tested by tape peeling and droplet impact.

FINDINGS

The novel combination of hydrophobic silica (55 nm) and hydrophilic silica (200 nm) is essential in creating the hierarchical structures. By combining the strong adhesion of hydrophilic silica (bottom of coating film) to polymer substrates and porous structures of hydrophobic silica (top of coating film), we first time report a one-step and versatile approach to create uniform, transparent, robust, and superhydrophobic surface.