Self-healing Anticorrosive Coatings Research Articles

Satisfactory Tensile Strength and Strain of Recyclable Polyurethane with a Trimaleimide Structure for Thermal Self-Healing and Anticorrosive Coatings.

Bismaleimide (BMI) is often used as the cross-linking reagent in Diels-Alder (D-A)-type intrinsic self-healing materials (DISMs) to promote the connectivity of damaged surfaces based on reversible D-A bond formation on the molecular scale. Until now, although DISMs have exhibited great potential in the applications of various sensors, electronic skin, and artificial muscles, it is still difficult to prepare DISMs with satisfactory self-healing abilities and high tensile strengths and strains at the same time, thus largely limiting their applications in self-healing anticorrosive coatings. Herein, symmetrical trimaleimide (TMI) was successfully synthesized, and trimaleimide-structured D-A self-healing polyurethane (TMI-DA-PU) was prepared via the reversible D-A reaction (cycloaddition of furan and maleimide). As a DISM, TMI-DA-PU exhibits apparently higher self-healing efficiency (98.7%), tensile strength (25.4 MPa), and strain (1378%) compared to bismaleimide-structured D-A self-healing polyurethane (BMI-DA-PU) (self-healing efficiency, 90.2%; tensile strength, 19.3 MPa; strain, 1174%). In addition, TMI-DA-PU shows a high recycling efficiency (>95%) after 4 cycles of recycling. A series of characterizations indicate that TMI provides more monoene rings as the self-healing sites, forms denser cross-linked structures compared to BMI, and is, thus, more appropriate to be used for DISM applications. Moreover, the barrier abilities of coatings can be semi-quantitatively expressed by the impedance value at 0.01 Hz (|Z|0.01Hz). The |Z|0.01 Hz value of the TMI-DA-PU coating is 3.93 × 109 Ω cm2 on day 0, which is significantly higher than that of the BMI-DA-PU coating (6.76 × 108 Ω cm2 on day 0), indicating that the denser rigid cross-linked structure of TMI results in the small porosity in the TMI-DA-PU coating, thus effectively improving the anticorrosion performance. The construction of DISMs with the structure of TMI demonstrates immense potential in self-healing anticorrosive coatings.

The multiple faces of graphene on anticorrosion: Advances and prospects

In recent years, graphene has remarkably enhanced the protective performance of anticorrosive organic coatings, yielding increasingly frequent exciting results and perspectives. This paper reviews the latest research advancements that we have gathered on the influences of conductivity, modification, dispersion methods and controllable orientation of graphene; the graphene-based smart anticorrosive coatings; the current understandings on the designs of the anticorrosive coating and the action mechanisms of graphene in the coating. It is concluded that there would be greater opportunities for the gravitational field-induced method to play the shielding effect of graphene; noncovalent modification methods may not ensure satisfactory attachment of the modifiers to the surface; green modification methods are expected to reduce the electrical conductivity of graphene and covalently modify graphene; the self-healing and early-warning graphene-based anticorrosive coatings are becoming a trend in the development of anti-corrosive coatings. The current-faced challenges and the future development prospects of the graphene-based anticorrosive coating were also proposed. Although graphene performs well in anticorrosive coatings, there is still considerable room to improve the performance, and a new round of industrial optimisation and upgrading in the anti-corrosion coating industry is inevitable with the rapid development of the anticorrosive graphene-based filler.

Fabrication of diisocyanate microcapsules for self-healing anti-corrosion coatings via integrating electrospraying and interfacial polymerization

Epoxy resins serve as useful material in anti-corrosion coatings. However, the development of microcracks during the processing or service life of a coating is an inevitable occurrence that markedly degrades its performance and shortens its lifespan. The incorporation of self-healing materials can prolong the coatings' lifespan and enhance the reliability of corrosion prevention processes. In this study, a microencapsulation method via integrating electrospraying and interfacial polymerization (ES-IP) was adopted to synthesize the microcapsules containing 4,4’-bis-methylene cyclohexane diisocyanate (HMDI) successfully. The self-healing capability of these microcapsules within the anti-corrosion coating was successfully validated. The prepared HMDI microcapsules (HMDI-MCs) demonstrate excellent dispersibility, tunable characteristics, and a high core material content of 93 wt%. Self-healing anti-corrosion coatings containing HMDI-MCs were prepared and underwent accelerated corrosion testing in sodium chloride (NaCl) solution. The result showed that HMDI is capable of leaking from microcapsules and undergoing solidification, thus forming a barrier to metal steel from corrosion hazards by endowing the coatings with effective self-healing abilities. This paper expands the application of the ES-IP technique in microencapsulation and suggests that HMDI-MCs have significant potential in self-healing anti-corrosion coating.

Fabrication of photothermal responsive dual-chamber microcapsules for self-healing epoxy anticorrosion coatings

It has been urgent that timely repair of microdamage generated during long-term service of metal insulation coatings. Hereby, we developed a novel self-healing dual-chamber microcapsule with particle size about 5 μm, in which furfuryl amine modified polystyrene-acrylic acid (PSAF) as shell material and photosensitizer Carbon dots (CDs) as Pickering emulsifier. The synthesized materials were characterized analytically, FTIR and DSC demonstrated the simultaneously existence of healing agent and curing agent in the resultant dual-chamber microcapsule. Experiments also showed microcapsules exhibited satisfying storage stability more than 20 d at room temperature as well as thermogenesis effect that allowing temperature of epoxy composite materials raised to 50 °C in 60s and fractures to be effectively minimized in time. The scratch tensile measurement results demonstrated that epoxy resin composites incorporated with 2 wt% microcapsules exhibited the optimal strength self-healing efficiency, modulus, toughness and anti-fatigue performance. Furthermore, surface characterization and EIS analysis also confirmed the long-lasting healing effect of EP/MC2% complex coating with outstanding corrosion resistance. Therefore, the photothermal responsive dual-chamber microcapsule designed in this work has application as self-healing material especially epoxy anti-corrosion coating.

Tough rosin-based reversibly crosslinked elastomers with anticorrosion and adhesion properties

Conventional polymer materials cannot repair hidden cracks that appear during use by themselves, which affects service life and reliability. The reversibility of dynamic covalent bonds provides an effective approach for the sustainable development of materials. In this study, we introduced rosin, a renewable resource, and dimethylglyoxime with an oxime bond into polyurethane elastomers to prepare tough, self-healing rosin-based crosslinked elastomers. Benefiting from their high crosslinking density, the prepared elastomers exhibit excellent mechanical properties (tensile strength up to 13.6 ± 0.5 MPa and toughness up to 21.3 ± 0.6 MJ m–3) and solvent resistance. Based on the dynamic reversibility of oxime–carbamate bonds, the elastomers exhibit excellent self-healing properties (97.2 ± 1.1 % self-healing efficiency for 3 h at 80 °C). Furthermore, the elastomers exhibit good adhesion and corrosion resistance. Notably, the addition of rosin improves the elastomers' hydrophobicity and heat resistance in addition to their mechanical properties. These findings suggest that the prepared self-healing rosin-based elastomers have promising applications in self-healing anticorrosive coatings and adhesives.

Dual templated-based synthesis of smart zeolites and its self-healing anticorrosion coatings

The process for the synthesis of smart zeolite is complex. The porous zeolite was synthesized by a hydrothermal route. Aluminium powder and tetraethyl orthosilicate (TEOS) are used as alumina and silica sources. The presence of tetrapropylammonium hydroxide (TPAH) and sodium dodecyl benzene sulphonic acid (SDBS) acts as a structural directing agent and soft templates. The chemical growth mechanism of porous zeolite to form needle structures with the help of templates is discussed. The porous zeolite was prepared using optimum crystallization conditions (temperature and duration) and Si/Al component ratios. Following calcination, the porous zeolite was loaded with mercaptobezothaizole (MBT) and layer by layer (LBL) covered with both cationic and anionic polyelectrolytes. This is the first time a study has been conducted that embraces the porous zeolite pre-loaded with a corrosion inhibitor (MBT). Here, the MBT is released in high pH conditions to prevent corrosion, simultaneously increasing the life of the smart zeolite coatings in a corrosive environment. The smart zeolite-based coatings prevent corrosion by the pH activity of smart zeolite above the neutral pH condition.

Infrared-responsive shape memory self-healing and fluorescent damage-indication anti-corrosion coatings for aluminum alloys

Infrared-responsive shape memory self-healing and fluorescent damage-indication anti-corrosion coatings for aluminum alloys

Damage-indicating and self-healing anticorrosion coatings based on fluorescence resonance energy transfer and photothermal shape memory mechanism

Self-healing coatings, which possess the ability to repair damage and restore corrosion resistance without significant human intervention, have become a hot topic in corrosion protection research. In this paper, (±)-10-camphorsulfonic acid-doped polyaniline is synthesized and then combined with copolyurethane (copPU) to form the photothermal shape memory composite polymer (CSPA-copPU). An aggregation-induced emission agent, named N’,2-bis[(E)-5-chloro-2-hydroxybenzylidene] hydrazine-1-carbohydrazide, is synthesized and applied to create a synergistic fluorescence system with a prepared chelation-enhanced fluorescence (CHEF) agent, named Rhodamine Benzimidazole. Under the CHEF behavior in response to Fe3+ and the fluorescence resonance energy transfer effect, the system exhibits a strong and sensitive fluorescence response to corrosion-generated Fe3+. Using electrospinning technology, CSPA-copPU@Fl fibers are prepared with CSPA-copPU as the shell and a mixture of fluorescent agents as the core solution and applied to create the composite coatings. The coatings effectively indicate damage in the form of fluorescence, providing guidance for infrared laser repair. CSPA facilitates the passivation of exposed steel. Under irradiation by an infrared laser, the surface temperature reaches the glass transition temperature of copPU and the epoxy binder. Through softening expansion and diffusion entanglement of molecular chains, scratches in the coatings are closed and repaired, and the corrosion resistance is restored to a level of intact coatings.

Preparation of fully epoxy resin microcapsules and their application in self-healing epoxy anti-corrosion coatings

Herein, an innovative self-healing epoxy coating with outstanding corrosion resistance has been developed. The self-healing capability of the coating is achieved by embedding microcapsules, comprising of solidified epoxy resin as the outer layer and liquid epoxy resin as the inner content. The chemical composition of the microcapsule wall is identical to that of the coating substrate, it is equivalent to injecting the liquid repair agent directly into the coating. Remarkably, due to the absence of any additional components in the coating system, the microcapsules seamlessly integrate with the resin matrix of the coating, showcasing exceptional compatibility.

The novel damage-reporting and self-healing coatings prepared by electrospinning technology based on AIE agents and photothermal shape memory polymer

The self-healing coatings for metals aroused researchers' interest due to their spontaneous repair of coating damage. In this study, intelligent damage-reporting and self-healing anti-corrosion coatings were developed using electrospun fiber as the core functional materials. The fibers exhibited core–shell structures, with the core materials being the solutions of the composite fluorescence probe RTPE. The shell materials consisted of the photothermal shape memory polymer, namely, phosphotungstic acid modified polyaniline-polyurethane composite polymer. Rhodamine Tetraphenylethylene (RTPE) demonstrated water-triggered aggregation-induced emission (AIE) effects and also exhibited fluorescence response to corrosive factors such as hydrogen ions and iron ions at the damaged area of the coatings. Under the trigger of the infrared laser, the modified polyaniline converted light energy into heat, causing the softening of epoxy and the shape memory effect of polyurethane. These processes facilitated the closure and repair of the damage, thus restoring their anti-corrosion functionality. Phosphotungstic acid played a role in enhancing the photothermal efficiency. The self-healing mechanism reinforced the corrosion resistance of the coatings. The self-indicating feature for damaged areas provided guidance for artificial repair in regions that did not self-heal satisfactorily. The synergistic and intelligent functionalities of the prepared coatings foreshadowed the significant potential applications in marine and aerospace corrosion protection fields.

Review on aviation intelligent self-healing anti-corrosion coating

Purpose This paper aims to focus on the research progress of intelligent self-healing anti-corrosion coatings in the aviation field in the past few years. The paper provides certain literature review supports and development direction suggestions for future research on intelligent self-healing coatings in aviation. Design/methodology/approach This mini-review uses a systematic literature review process to provide a comprehensive and up-to-date review of intelligent self-healing anti-corrosion coatings that have been researched and applied in the field of aviation in recent years. In total, 64 articles published in journals in this field in the last few years were analysed in this paper. Findings The authors conclude that the incorporation of multiple external stimulus-response mechanisms makes the coatings smarter in addition to their original self-healing corrosion protection function. In the future, further research is still needed in the research and development of new coating materials, the synergistic release of multiple self-healing mechanisms, coating preparation technology and corrosion monitoring technology. Originality/value To the best of the authors’ knowledge, this is one of the few systematic literature reviews on intelligent self-healing anti-corrosion coatings in aviation. The authors provide a comprehensive overview of the topical issues of such coatings and present their views and opinions by discussing the opportunities and challenges that self-healing coatings will face in future development.

Self-healing anticorrosive coatings inspired by the biomimetic porous organic cage nanocontainer for mussels

In harsh corrosive environments such as deep sea, it cannot meet the requirements of long-term anticorrosion by uniquely increasing the physical barrier property of a coating with lamellar Ti3C2Tx nanosheets. Thus, it is quite desirable to acquire exciting anticorrosion applications through a skillful combination of a self-healing property with the physical barrier property of lamellar nanosheets. Inspired by the adhesion mechanisms of mussels, we successfully fabricated a porous organic cage (HNQ-EN) with adhesive nature as a nanocontainer. It could easily combine with Ti3C2Tx nanosheets and advance the compatibility between Ti3C2Tx and organic resin. Meantime, the porous structure of HNQ-EN enables it to accommodate various guest molecules, such as green cerium nitrate corrosion inhibitor. The introduction of HE-Ti3C2Tx-Ce in 3.5 wt% NaCl solution made the inhibition efficiency from the initial 7.8% increase to 91.1% after immersion for 36 h. It derived from the successful release of Ce3+ from HNQ-EN and forming cerium deposited film. For the composite coating containing HE-Ti3C2Tx-Ce (EP/HE-Ti3C2Tx-Ce), the LEIS results demonstrated it showed self-healing performance provided by Ce3+. Moreover, the lowest Zf = 0.01 Hz value for EP/HE-Ti3C2Tx-Ce coating reached 4.41 × 106 Ω cm2 after immersion for 36 h, which was one magnitude larger than that of EP coating.

Intelligent self-healing anti-corrosive coatings with crosslinked conducting polypyrrole hydrogel network

The cross-linked conducting polypyrrole hydrogel (CPH) network is designed for preparing the corrosion-resistant and self-healing epoxy coatings, which are used for the long-term active corrosion control of Mg alloys substrate in 3.5 wt% NaCl solution. The encapsulated phytic acid (PA) inhibitors are uniformly distributed in the crosslinked CPH network with an encapsulation amount of 16.77%. The inductively coupled plasma–optical emission spectrometry test indicates that the releasing rate of the PA inhibitors from the crosslinked CPH network rises with the increased pH values, reflecting their pH-responsive feature. Afterward, the epoxy coatings impregnated with various contents of the CPH network are coated on the Mg alloy surface, and their corrosion resistance and self-healing performances are evaluated using electrochemical and immersion tests. Results indicate that the epoxy coatings with 5 wt% CPH displays the most durable corrosion-resistant and self-healing performances with the highest coating resistance (4.39 × 105 Ω cm2) and charge-transfer resistance (8.28 × 105 Ω cm2) values even after 28 days of immersion. The encapsulated PA inhibitors continuously release to the cracked region in response to the local pH variations and react with Mg2+ ions generated from the active corrosion site. Consequently, an Mg-PA protective layer is formed to suppress further corrosion activities. Both the enhanced inherent barrier effect of epoxy coatings, the pH-responsive release behaviors of the PA inhibitors from crosslinked CPH network and the durable anodic protection effect of CPH are beneficial for improving the anti-corrosive performance of the epoxy coatings. It is believed that this kind of crosslinked CPH network will provide a new strategy for designing highly self-healing and anti-corrosive performance of epoxy coatings for the active corrosion control of other metals.

Advances in self-healing anticorrosive coatings

Advances in self-healing anticorrosive coatings

Fabrication of graphene oxide-modified self-healing microcapsules for Cardanol-based epoxy anti-corrosion coatings

In this paper, graphene oxide (GO) modified microcapsules have been developed for use in self-healing Cardanol-based epoxy anti-corrosion coatings on steel substrates. The microcapsules had a polymethyl methacrylate (PMMA) shell, covered with aminated GO flakes and contained either of the two complementary healing agents mixed with nanosized GO flakes. One set of capsules contained epoxidized nanosized GO and Cardanol-based epoxy resin, while the other contained aminated nanosized GO and Cardanol-based amine curing agent. The microcapsules had a narrow size distribution with a peak value of 4 μm. The Cardanol-based coatings containing various fractions of up to 20 wt% microcapsules in their stoichiometric ratio showed excellent anti-corrosion and self-healing properties. FT-IR, XPS, AFM, and Raman spectroscopy were used to characterize the size and chemical composition of the GO. Optical microscopy and SEM were used for morphological characterization. Double cantilever test upon bulk samples showed an excellent load transfer across the fracture plane after only 1 day curing at room temperature. The anti-corrosion properties of the Cardanol-based coating containing the two-component microcapsules were tested using electrochemical impedance spectroscopy (EIS). It was found that, after 60-day immersion in 3.5 wt% NaCl solution, the low-frequency impedance modulus |Z|0.01Hz of the Cardanol-based coating containing GO-modified microcapsules was three orders of magnitude higher than that of the systems with capsules without GO. After scratching the coating containing 20 wt% GO-modified microcapsules and exposing it to an aqueous 3.5 wt% NaCl solution, the |Z|0.01Hz of the Cardanol-based coating returned over a period of 7 days to the original value.

Engineering Active-Site-Induced Homogeneous Growth of Polydopamine Nanocontainers on Loading-Enhanced Ultrathin Graphene for Smart Self-Healing Anticorrosion Coatings

Engineering nanocontainers with encapsulated inhibitors onto graphene has been an emerging technology for developing self-healing anticorrosion coatings. However, the loading contents of inhibitors are commonly limited by inhomogeneous nanostructures of graphene platforms. Here, we propose an activation-induced ultrathin graphene platform (UG-BP) with the homogeneous growth of polydopamine (PDA) nanocontainers encapsulated with benzotriazole (BTA). Ultrathin graphene prepared by catalytic exfoliation and etching activation provides an ideal platform with an ultrahigh specific surface area (1646.8 m2/g) and homogeneous active sites for the growth of PDA nanocontainers, which achieves a high loading content of inhibitors (40 wt %). The obtained UG-BP platform exhibits pH-sensitive corrosion inhibition effects due to its charged groups. The epoxy/UG-BP coating possesses integrated properties of enhanced mechanical properties (>94%), efficient pH-sensitive self-healing behaviors (98.5% healing efficiency over 7 days), and excellent anticorrosion performance (4.21 × 109 Ω·cm2 over 60 days), which stands out from previous related works. Moreover, the interfacial anticorrosion mechanism of UG-BP is revealed in detail, which can inhibit the oxidation of Fe2+ and promote the passivation of corrosion products by a dehydration process. This work provides a universal activation-induced strategy for developing loading-enhanced and tailor-made graphene platforms in extended smart systems and demonstrates a promising smart self-healing coating for advanced anticorrosion applications.

The preparation of linseed oil loaded graphene/polyaniline microcapsule via emulsion template method for self-healing anticorrosion coatings

A novel kind of graphene/polyaniline hybrid microcapsules loaded with self-healing agent (linseed oil, LO) were synthesized by Pickering emulsion template method in this work. In our strategy, graphene oxide (GO) was used as Pickering emulsifier to stabilize emulsion droplet containing aniline and linseed oil. After the polymerization of aniline, graphene/polyaniline microcapsules loaded with linseed oil (LO@GO/PANI) were prepared. By adjusting GO concentration and oil-water ratio, the size of the emulsion droplet and LO@GO/PANI microcapsule can be controlled at about 15–20 µm. The successful synthesis of LO@GO/PANI microcapsules was proved by SEM, FT-IR and TGA. The unique GO/PANI hybrid shell combined the outstanding barrier property of GO and anti-corrosion function of PANI. The solvent resistance results showed that the as-prepared microcapsules possessed stronger resistance to organic solvents. A smart coating with dual functions of anti-corrosion and self-healing was prepared by dispersing the as-prepared LO@GO/PANI microcapsule in waterborne epoxy resin. As the contents of microcapsules was 10 wt%, the scratch of the coating was completely healed after 12 h observed from the microscope images. The electrochemical impedance spectroscopy (EIS) and salt spray test all verified that the incorporation of microcapsules could significantly improve the anti-corrosion performance of the water-borne coatings. After 40 days' immersion, the low frequency modulus of the composite coating was almost 2 orders of magnitude higher than that of pure epoxy coating, and no obvious corrosion product was observed after 500 h salt spray test.

Photothermal-Responsive Wormlike Polydopamine-Wrapped Ethylene-Vinyl Acetate Copolymer toward Triple-Action Self-Healing Anticorrosion Coating

The design and synthesis of smart polymeric coatings with excellent self-healing and interfacial adhesion capability are highly pursued for anticorrosion applications. Herein, a unique strategy for triple-action self-healing anticorrosion coatings was applied by the cooperation of the crack closure, healing agent filling, and corrosion inhibition effects. The coating system was constructed by the combination of wormlike polydopamine wrapped ethylene vinyl acetate microspheres (PDA@EVA) and a shape memory epoxy network. Owing to the prominent photothermal characteristic of PDA, the shape memory coating exhibits rapid crack closure property with near-infrared (NIR) irradiation. Meanwhile, the local high temperature promotes the melting and flow of designed wormlike EVA to fill the defects. Morphology investigations revealed that the coating scratch can be promptly healed with 90 s of NIR irradiation. Except as a photothermal agent, PDA can also coordinate with metal substrate, further inhibiting localized corrosion and strengthening the coating/metal interfacial interaction. Electrochemical measurements proved that the local corrosion reactivity was significantly inhibited and the coating resistance also recovered. In addition, the adhesion strength of PDA@EVA embedded coating reaches 7.6 MPa after a healing process, which is about 84% of intact coating. This strategy presented here provides avenues for developing smart protective coatings with high healing efficiency and service durability.

Rapid and eco-friendly one-step synthesis of dodecylamine-encapsulated mesoporous silica nanocontainers

Incorporating nanoreservoirs loaded with corrosion inhibitors is the most attractive approach for developing extrinsic self-healing anti-corrosion coatings. This work reports a rapid and eco-friendly one-step synthesis of dodecylamine-encapsulated mesoporous silica nanocontainers. The nanocontainers were characterized by X-ray diffraction, electron microscopy and thermogravimetric analysis. The as-synthesized nanocontainers were amorphous with short-range ordered mesoporous channels. Thermogravimetric study confirmed the inhibitor loading to be ∼13.6%. The nanocontainers (1 wt%) were further dispersed in 0.1 mol/L NaCl solution, and the release behaviour was systematically studied as a function of pH (acidic, basic and neutral) by electrochemical impedance spectroscopy at different durations. The release was more pronounced at acidic pH ranges. The inhibitor-loaded nanocontainers provided significantly higher impedance values in acidic environment revealing sustained inhibitor release and enhanced corrosion protection for the carbon steel electrode. The study also reports detailed thermogravimetric results on the effect of different washing procedures in determining the inhibitor percentage loading.

Controllable group tailoring enables enhanced pH-responsive behaviors of polydopamine delivery system in smart self-healing anticorrosion coatings

Nanomaterials as delivery systems loaded with corrosion inhibitors is a promising strategy for achieving self-healing anticorrosion coatings. However, the uncontrollable passive release of inhibitors brings challenges for scalable anticorrosion applications in different environments with wide-range pH values. Here, we propose an effective strategy for regulating the pH-responsive behaviors of polydopamine (PDA) delivery system by controllable group tailoring to enhance the corrosion inhibition effects in different environments. The delivery system (BTA@PDA) consisting of PDA and benzotriazole (BTA) were prepared by a convenient one-pot method. Based on the pH-dependent changes in charge of amine groups and hydroxyl groups, BTA@PDA showed the enhanced corrosion inhibition effects in acid or alkaline environments. Electrochemical impedance spectroscopy and energy dispersive spectroscopy were performed to characterize the self-healing behavior of scratched coatings added with BTA@PDA. The scratched coatings exhibited an increased impedance modulus due to the dual corrosion inhibition effects of BTA and PDA, triggered by the corrosion-induced pH variation. Moreover, the impedance modulus of the coating maintained at 2.03 × 109 Ω cm2 after 21 days of immersion (only 1.06 × 108 Ω cm2 for an epoxy coating). This study has a great significance for the design of pH-responsive smart coatings for scalable applications in different environments.