Long-term corrosion protection for magnesium alloy by two-layer self-healing superamphiphobic coatings based on shape memory polymers and attapulgite

Triple Corrosion Protection: Dual-Layer Coating with Simultaneous Superhydrophobicity, Intelligent Self-Healing, and Shape Memory

In this paper, a self-healing superhydrophobic smart two-layer coating, ZOA/SMP-S, was developed. ZIF-8 was surface hydrophobically modified by octadecylphosphoric acid (OPA) to obtain Z-OPA and then encapsulated with a corrosion inhibitor, AMT ( 2-Amino-5-mercapto-1,3,4-thiadiazole), to obtain the superhydrophobic nanocontainers, ZOA. ZOA was embedded into the SMP (shape memory coating) to obtain the smart coating, and Z-OPA was sprayed to obtain the second superhydrophobic coating. SEM showed that the scratch coatings were rapidly reduced by scratches after a simple heat treatment. The prepared composite coatings showed excellent performance in corrosion inhibitor release, immersion, superhydrophobicity, and self-healing experiments. The contact angle of the superhydrophobic coating reached 158.2°, and the sliding angle was 2.8°. The low-frequency impedance value |Z|f=0.01 Hz of ZOA/SMP-S is as high as 1.58 × 1010 Ω·cm2 after 40 days of immersion test, which indicates that the triple protection greatly enhances the corrosion resistance of the coating.

Self-Healing Superhydrophobic Coatings with Multiphase Repellence Property

Developing versatile, scalable, and durable coatings that repel various matters in different service environments is of great importance for engineered materials applications but remains highly challenging. Here, the mesoporous silica microspheres (HMS) fabricated by the hard template method were utilized as micro-nanocontainers to encapsulate the hydrophobic agent of perfluorooctyltriethoxysilane (F13) and the corrosion inhibitor of benzotriazole (BTA), forming the functional microsphere of F-HMS(BTA). Moreover, the synthesized organosilane-modified silica sol adhesive (SMP) and F-HMS(BTA) were further employed as the binder and functional filler to construct a superhydrophobic self-healing coating of SMP@F-HMS(BTA) on various engineering metals through scalable spraying. The prepared coating exhibits good mechanical durability and strong resistance to accretion of multiphase substances including large molecule compounds, liquids, and ice crystals, demonstrating good antifouling and anti-icing properties. Moreover, the coatings possess hydrophobic and anticorrosion self-healing properties owing to the self-migration release of the functional additives in the micro-nanocontainers, showing the "active-passive" synergistic properties mechanism. At a frequency of 0.01 Hz, the charge transfer resistance Rct and the constant phase element Ccpe were measured to be 2.62 × 109 Ω cm2 and 9.63 × 10-10 F cm2, respectively. In addition, the corrosion current density was reduced by 3-5 orders of magnitude, indicating superior corrosion resistance. This work provides a feasible strategy to prepare functional protective coatings for a wide range of applications in addressing adhesion and corrosion issues.

High-performance insulating materials with high breakdown strength and low permittivity for eco-friendly electrical equipment

High-performance insulating materials are essential for developing lightweight, compact, and green offshore wind power equipment. It has been shown that nanoporous structures can limit the development of electron avalanche, leading to a significant increase in the breakdown electric strength of dielectrics. Hence, we fabricated a polysiloxane nanoporous biopolymer insulating material (PNBIM) with the nanoporous structure that presents exceptionally high electrically insulating properties. Under a CO2 atmosphere, the breakdown electric strength of the PNBIM was remarkably improved, exhibiting 761.01 % enhancement relative to that of the pure gas gap. Moreover, the PNBIM demonstrates excellent dielectric performance, with a low dielectric constant (1.63) and dielectric loss (0.014), as well as high hydrophobicity and excellent thermal stability. The investigations revealed that the nanopores inside the material can effectively suppress gas discharge and improve the breakdown electric strength. This study widens our understanding of conventional insulating materials and provides a promising approach for exploring high-performance insulating materials provide valuable insights.

Durable Superhydrophobic Coatings with Attapulgite for Inhibiting 5G Radome Rain Attenuation

5G radomes are easily wetted and stained by rainfall, which greatly reduces the quality of signal transmission. Superhydrophobic coatings are expected to solve this problem because of their unique wettability, but it is still challenging to develop robust superhydrophobic coatings via simple methods. Here, we report the design of robust superhydrophobic coatings containing oxalic acid-modified attapulgite (MDP) for inhibiting rain attenuation of 5G radomes. First, a homogeneous suspension was prepared by nonsolvent-induced phase separation of a silicone-modified polyester adhesive (SMPA) solution containing fluorinated MDP (F-MDP) nanorods. Superhydrophobic coatings can be easily prepared by spraying the suspension. The effects of phase separation and the SMPA/F-MDP ratio on the surface morphology, superhydrophobicity, and stability of the coatings were systematically investigated. The micro-/nanostructure and low surface energy endow the coatings with excellent static and dynamic superhydrophobicity. Compared with previous studies, the coatings exhibit excellent mechanical stability, flexibility, chemical stability, and pressure resistance due to the combined effects of adhesion by SMPA, self-similar micro-/nanostructures, reinforcement by the MDP nanorods, etc. Consequently, the coatings show good performance in preventing rain attenuation of 5G radomes, an emerging application of Superhydrophobic coatings. We believe that the coatings have great application potential in various fields, including 5G communication.

Superhydrophobic Polyaniline-Siloxane Coatings with Excellent Barrier and Active Corrosion Protection Properties for Mild Steel

Although superhydrophobic surfaces have attracted much attention in research, their high cost, poor durability, and challenging manufacturing processes have prevented their widespread application. Here, we describe a simple method of preparing superhydrophobic polyaniline (PANI) pigments and their application in protective coatings. Doping polyaniline pigments with low surface energy perfluorodecanoic acid (PFDA) allowed them to overcome their intrinsic high surface energy, and the resultant PANI-PFDA pigments showed superhydrophobicity. The superhydrophobic PANI-PFDA pigments with different weight percentages were incorporated into a polydimethylsiloxane (PDMS) coating to prepare the superhydrophobic coating. We endeavored to examine the role that hydrophobicity played in enhancing corrosion resistance and looked into the highest concentration of pigment that the coating could withstand. Additionally, studies were carried out on the coating's adherence to the metal and the stability of hydrophobicity at various pH levels. The results showed that PANI-PFDA pigments improved the hydrophobicity and corrosion resistance in the PDMS coating without compromising its robustness and durability. Electrochemical impedance spectroscopy studies revealed that 40 wt % PANI-PFDA content in the PDMS coating provided the best corrosion protection, and this coating could offer active corrosion protection when an artificial defect was made in the coating.

Attapulgite-Based Stable Superhydrophobic Coatings for Preventing Rain Attenuation of 5G Radomes

Superhydrophobic coatings hold immense promise for various applications. However, their practical use is currently hindered by issues such as poor stability, high costs, and complex preparation processes. Here, we present the preparation of cost-effective and stable superhydrophobic coatings through fluorination of natural attapulgite (F-ATP) nanorods and subsequent solvent-induced phase separation of a silicone-modified polyester adhesive (SMPA) with the F-ATP nanorods dispersed in it. Phase separation of the F-ATP/SMPA system forms a uniform suspension of microaggregates, which can be easily utilized for preparing superhydrophobic coatings via spray coating. The coatings have a low-surface-energy hierarchical micro/nanostructure due to phase separation of SMPA and adhesion of F-ATP to it. Moreover, the effects of the solvent composition (i.e., phase separation degree of SMPA) and the SMPA/F-ATP mass ratio on the morphology, superhydrophobicity, and stability of the coatings were investigated. After systematic optimization, the coatings exhibit excellent static and dynamic superhydrophobicity as well as high mechanical, chemical, thermal, and UV aging stability. Finally, the coatings were applied to the 5G radome surface and showed good rain attenuation prevention performance. Thus, we are confident that the superhydrophobic coatings have great application potential due to their advantages of outstanding performance, straightforward preparation procedures, cost-effectiveness, etc.

Challenges and strategies for commercialization and widespread practical applications of superhydrophobic surfaces

Superhydrophobic (SH) surfaces have progressed rapidly in fundamental research over the past 20 years, but their practical applications lag far behind. In this perspective, we first present the findings of a survey on the current state of SH surfaces including fundamental research, patenting, and commercialization. On the basis of the survey and our experience, this perspective explores the challenges and strategies for commercialization and widespread practical applications of SH surfaces. The comprehensive performances, preparation methods, and application scenarios of SH surfaces are the major constraints. These challenges should be addressed simultaneously, and the actionable strategies are provided. We then highlight the standard test methods of the comprehensive performances including mechanical stability, impalement resistance, and weather resistance. Last, the prospects of SH surfaces in the future are discussed. We anticipate that SH surfaces may be widely commercialized and used in practical applications around the year 2035 through combination of the suggested strategies and input from both academia and industry.

Application of Shape Memory and Self-Healable Polymers/Composites in the Biomedical Field: A Review

Shape memory-assisted self-healing polymers have drawn attention over the past few years owing to their interdisciplinary and wide range of applications. Self-healing and shape memory are two approaches used to improve the applicability of polymers in the biomedical field. Combining both these approaches in a polymer composite opens new possibilities for its use in biomedical applications, such as the "close then heal" concept, which uses the shape memory capabilities of polymers to bring injured sections together to promote autonomous healing. This review focuses on using shape memory-assisted self-healing approaches along with their respective affecting factors for biomedical applications such as tissue engineering, drug delivery, biomaterial-inks, and 4D printed scaffolds, soft actuators, wearable electronics, etc. In addition, quantification of self-healing and shape memory efficiency is also discussed. The challenges and prospects of these polymers for biomedical applications have been summarized.

Self-healing system of superhydrophobic surfaces inspired from and beyond nature

Superhydrophobic surfaces show wide prospects in a variety of applications requiring self-cleaning, anti-fog, anti-ice, anti-corrosion and anti-fouling properties, which have attracted the attention of many researchers. However, superhydrophobic surfaces are inevitably affected by chemical corrosion, scratches and wear in practical applications, resulting in the loss of superhydrophobicity. To solve this problem, researchers have developed superhydrophobic surfaces with self-healing properties. In this paper, the research achievements of self-healing superhydrophobic materials in recent years are summarized, and the preparation and repair principle of self-healing superhydrophobic surfaces are introduced from three aspects: surface chemical composition repair, surface roughness repair and double repair. In addition, some multifunctional self-healing superhydrophobic surfaces are introduced, such as conductive, stretchable, antibacterial, etc. Finally, in order to provide a reference for the preparation of widely used long-acting superhydrophobic materials, some existing problems and future development prospects are described in order to attract more researchers' attention and promote the development of this field.

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.

Construction of durable superhydrophobic and anti-icing coatings via incorporating boroxine cross-linked silicone elastomers with good self-healability

The fragility of the micro-nano structure makes superhydrophobic coatings highly susceptible to stress, resulting in a decrease in their superhydrophobic and anti-icing performance. In this work, we proposed a new insight to improve durability by incorporating a thin layer of self-healable elastomer with a dynamic network on the micro-nano structure. We constructed superhydrophobic coatings (EP/SiO₂/BFVSE) with a three-layered structure of the epoxy resin/silica nanoparticle/silicon elastomer. The silicon elastomer (BFVES) with a B-O dynamic cross-linked network and fluorinated moieties was synthesized by graft polymerization on vinyl silicon oil. The preparation route is facile and convenient for mass production. BFVES has rapid self-healing properties for scratches at room-temperature, underwater and at -18 °C. EP/SiO₂/BFVSE preserved apparently higher CAs after being immersed in pH = 1, pH = 13, and NaCl solutions for 96 h as compared with the EP/SiO₂ coating. In a water striking environment, the CA of EP/SiO₂/BFVSE was slightly decreased to 153°. SEM images further reveal that the recovery of superhydrophobicity and icephobicity is attributed to the self-healing behavior of the boroxine-containing silicon elastomer. The EP/SiO₂/BFVSE coating also possesses additional self-healing ability under chemical oxidation. The high durability of the self-healable superhydrophobic coating enables great application potential in aircraft, marine vessels, and outdoor facilities in harsh environments.

Long-Term Static and Dynamic Corrosion Stability of Nonwetting Surfaces

Superhydrophobic surfaces (SHSs) and lubricant-infused surfaces (LISs) are two classes of nonwetting surfaces that have drawn attention due to their advanced functional properties including corrosion inhibition. Yet there is a conspicuous lack of corrosion study of SHSs and LISs with respect to their fabrication and material parameters, especially at high temperatures and under dynamic flow conditions over long durations, which is sought to be addressed in this article. Considering copper SHSs and LISs, a full factorial combinatorial study of two facile texturing processes, electrodeposition and etching, two different functionalization agents, stearic acid and mercaptan, and two types of infused lubricants, Krytox 104 and DOWSIL 510, is presented, encompassing over 650 measurements on 90 tested surfaces. All fabricated surfaces demonstrated water repellency with a contact angle above 150° and a sliding angle below 7°. For the first time, the study examines high-temperature corrosion stability and long-term corrosion durability of the nonwetting surfaces in both static fluid and dynamic turbulent flow conditions over a period of 30 days. LISs and SHSs are shown to provide excellent corrosion inhibition over all tested corrosion conditions, with negligible presence of corrosion species on the surfaces and no deterioration of the texturing. The surfaces are also shown to rejuvenate easily to the initial wettability and corrosion resistance values. This study provides valuable insights into the selection of materials and processing parameters for the fabrication of nonwetting surfaces for the application of interest.

Enhanced Shape Memory Metal-Coordinated Poly(aryl ether ketone)s with Tunable Gradient-Deformation Behaviors as well as Self-Healing and Reprocessing Abilities

Reversible dynamic bonds are able to crack and recombine upon external stimuli, which endow polymers with exceptional self-healing, reprocessing, and reversible deformation ability. In this paper, we integrated the metal coordination bonds into shape memory poly(aryl ether ketone) (PAEK) to fabricate smart materials with multifunctionalities. Through tuning the metal ion content and species, the enhancement of shape memory behaviors was achieved, including the high recovery ratio (over 98%) and fixity ratio (over 98%), which was closely related to the synergic effect of the intrinsic motion ability of PAEK matrix and the cracking-recombination of coordination bonds. Besides, through the combination of the components with different Cu²⁺ contents, in addition to the components with Fe²⁺ coordination bonds, we fabricated the gradient shape memory structures with controllable shape memory and recovery behaviors. The manipulation of gradient coordination bonds resulted in different shape recovery speeds and directions. Furthermore, due to the dynamic cracking-recombination of coordination bonds, the metal-coordinated PAEK material exhibited the great self-healing and reprocessing performances, which were significant for largely extending its application range.

The Potential of the Superhydrophobic State to Protect Magnesium Alloy against Corrosion

We describe the technologically simple route for the fabrication of the superhydrophobic coatings on top of wrought magnesium alloy MA8 based on nanosecond laser processing followed by the chemical vapor deposition of fluorosilane. The chemical and phase composition, surface morphologies, and variation of the coating wettability during prolonged contact with 0.5 NaCl solution or with salt aerosol were characterized using X-ray diffraction, FT-IR spectroscopy, scanning electron microscopy measurements, and the wettability analysis. The as-prepared coatings demonstrate corrosion current of more than eight orders of magnitude lower, while after 30 days of sample immersion into corrosive solution, the current was four orders of magnitude lower than that obtained for a polished sample which was for only 2 h in contact with electrolyte. The mechanisms of the protective activity of fabricated coatings were discussed.

Fabrication of Dual Self-Healing Multifunctional Coating Based on Multicompartment Microcapsules

By designing and preparing multifunctional materials exhibiting self-healing ability, problems related to their durability outdoors can be solved. This study, inspired by the self-healing mechanism of natural creatures, successfully prepared a dual self-healing multifunctional coating using temperature stimuli-responsive multicompartment microcapsules. Phase change materials (PCMs) were employed to load multicompartment microcapsules that were produced through Pickering emulsion polymerization by applying hydrophobic materials encapsulated by titanium dioxide (TiO₂) nanocapsules as Pickering emulsifiers. The multifunctional coating produced using microcapsules and self-healing waterborne polyurethane (WPU) exhibited thermal insulation and antireflection properties, which was attributed to the application of PCMs and TiO₂, and it also achieved remarkable superhydrophobicity. Moreover, this coating exhibited the intrinsic and superficial dual self-healing ability, which was attributed to the release of hydrophobic materials from microcapsules and the self-healing ability of WPU. This study can be referenced to guide the fabrication of high-performance self-healing materials, and it can contribute to the long-term use of multifunctional coatings.

Superhydrophobic Coatings with Photothermal Self-Healing Chemical Composition and Microstructure for Efficient Corrosion Protection of Magnesium Alloy

Self-healing superhydrophobic coatings have a wide potential for practical applications by prolonging their lifespan, but still suffer from some shortcomings, for example, difficulty in repairing microstructure damage, limited self-healing cycles, and more importantly the inability to self-heal while in service. Herein, we present the fabrication of superhydrophobic coatings having photothermal self-healing chemical composition and microstructure for the high performance anticorrosion of Mg alloy. The coatings contain a shape-memory polymer (SMP) primer and an upper superhydrophobic coating composed of fluorinated polysiloxane-modified multiwalled carbon nanotubes (PF-POS@MWCNTs). The coatings have good superhydrophobicity, photothermal effect, and anticorrosion performance. The coatings show excellent self-healing performance in response to chemical and microstructure damage, such as rapid self-healing under 1 sun irradiation in 10 min, complete self-healing after serious damage (e.g., 10 damage and self-healing cycles and complex microstructure damage), and even self-healing under natural sunlight in 4 h. Moreover, the self-healed coatings show good corrosion protection for magnesium alloy in the neutral salt spray test. These are because of the combination of the SMP primer with good shape-memory effect and the PF-POS@MWCNTs coating with good superhydrophobicity, photothermal effect, and embedded PF-POS. The coatings are self-healable under natural sunlight while in service and thus may find applications in diverse fields.

Superhydrophobic, superamphiphobic and SLIPS materials as anti-corrosion and anti-biofouling barriers

Multifunctional interfacial materials with special wettability including superhydrophobic, superamphiphobic, and SLIPS exhibited promising potentials for corrosion and biofouling resistance.