Self-healing Coatings Research Articles

Fabrication of amphiphilic self-healing coatings with high mechanical properties and their antifouling performance

A self-healing antifouling coating with excellent mechanical strength was prepared via a simple “one-step” method. A series of well-designed amphiphilic block copolymer polydimethylsiloxane-poly(2-(dimethylamino) ethyl methacrylate) (PDMS-PDMAEMA) synthesized by atom transfer radical polymerization was introduced to the self-healing polydimethylsiloxane-based polyurethane (PDMS-PU) system, which was further zwitterionized during solidification. The slight swelling resulting from zwitterionic segments promoted the contact fusion rate of the mechanically damaged parts, which improved the underwater self-healing ability of the resulting coating. The PDMS segments in both amphiphilic polymer and PU were entangled with each other to form a semi-interpenetrating network while the zwitterionic segments migrated externally when being immersed underwater, thus a micro-phase separation structure was obtained for antifouling coating. Qualitative and quantitative tests have also proved that the coating can significantly resist the adhesion of proteins (156 μg/cm2 vs 14 μg/cm2) and marine microorganisms (425 × 103 n/cm2 vs 12 × 103 n/cm2). In addition, the organically modified montmorillonite (MMT) effectively improved the coating's mechanical properties via coordination bonding, as the resulting coating's fracture strength was increased by 50 % compared with the initial PU coating. In this study, an inherent problem in underwater self-healing antifouling coatings is solved perfectly, that is to achieve self-healing properties without loss of mechanical properties, which provides inspiration for the research and development of novel self-healing antifouling coatings.

Porous 2D Ti3C2 MXene nanosheets sandwiched between imine-based covalent organic frameworks (COFs) for excellent corrosion protective coatings

MXene nanosheets have recently been the research hotspot for corrosion applications thanks to their 2D sheet-like structure and unique built-in physicochemical properties. However, they are prone to restacking and oxidation, narrowing down their final application. On the other hand, even highly exfoliated MXene does not possess a large surface area, which is desirable for self-healing and protective coatings. Thus, this study proposes a tailored hybrid skeleton by the in-situ growing of a highly porous covalent organic framework (COF) on the MXene nanosheets to avoid oxidation and restacking and, at the same time, enhance the MXene surface area. Such an advanced structural design is crucial for corrosion protective coatings since a sheet-like structure improves the barrier properties, while a large porous surface area is desirable for hosting corrosion inhibitors to provide self-healing features. As proof of concept, an imine-based COF was grown on the MXene nanosheet via an in-situ method, resulting in a 128 m2.g−1 surface area. Subsequently, loading zinc and glutamate molecules as inorganic and organic inhibitors into porous MXene nanosheets resulted in 88 % corrosion mitigation in the long term (96 h), which is promising among counterparts. Moreover, introducing this novel nanoplatform into an epoxy coating provided self-healing properties with more than 200 % active corrosion prevention improvement compared to the unfilled coating. Additionally, the proposed epoxy nanocomposite showed 10.64 Ω.cm2 for Log|Z|10 mHz term after 11 weeks in a 3.5 wt% saline solution, representing no electrolyte diffusion over a long period. In brief, this work proposes not only a novel structural design for superior anti-corrosion coatings but also a concept that has the potential to be applicable in various MXene-related areas.

Preparation of self-healing epoxy resin coatings based on dynamic disulfide bonds

Defects and mechanical damage that lead to peeling, corrosion and other potential hazards during practical applications are inevitable in epoxy coatings due to the high cross-link density of the epoxy network. Herein, the authors synthesized a self-healing polythiourethane (SPTU) material containing dynamic disulfide bonds for the design and preparation of an SPTU–epoxy coating. Fourier transform infrared spectroscopy, proton (1H) nuclear magnetic resonance spectroscopy and scanning electron microscopy showed that 2-hydroxyethyl disulfide was successfully introduced into the polythiourethane system. Due to the fracture and reattachment of double sulfur bonds, the 3% SPTU–epoxy coating exhibited good self-healing properties in scratch treatment, the scratch being repaired completely after 2 h at 85°C. Meanwhile, 75.7% of the tensile performance of the completely fractured 3% SPTU–epoxy sample was retained after self-healing. The Tafel polarization curve and electrochemical impedance spectroscopy results showed that the 3% SPTU–epoxy coating had excellent corrosion resistance and still provided considerable corrosion resistance after 19 days of immersion corrosion tests. The self-healing coating exhibited good self-healing ability under heating conditions, which is attributed to the bond breaking and reconnection of dynamic bonds provided by the self-healing component. The self-healing properties and corrosion resistance of the prepared coating effectively improve the service life of the epoxy coating and provide some guidance for corrosion protection of epoxy coatings.

Two combination strategies of coordinated silicon elastomer and modified nano-silica to fabricate self-healing hybrid coating@fabrics with high oil-water separation capabilities

With an increase in marine oil pollution, efficient remediation strategies are required to completely remove the oily wastewater. The construction of self-healing coatings with high separation efficiency has become a hot research topic. In this study, the hybrid coatings of nano-silica synergized with self-healing silicon elastomer were prepared on polyethylene terephthalate (PET) fabrics by two combination strategies. Different combination strategies conferred various bonding states between the nanoparticles and the elastomer, affecting the hydrophobicity and stability of the materials. Self-healing silicon elastomer was prepared based on polydimethylsiloxane (PDMS) crosslinked by iron-based coordination. The prepared hybrid fabrics exhibited high hydrophobicity with a water contact angle (WCA) of 145˚, and could maintain the hydrophobic properties after 20 cycles of mechanical abrasion. It realized 97% separation efficiency of multiple types of oil-water solution, even severe mechanical abrasion occurred, which still basically returned to the initial level after self-healing.

Self-healing and corrosion-sensing coatings based on pH-sensitive MOF-capped microcontainers for intelligent corrosion control

Organic coatings are one of the most used and versatile technologies to mitigate corrosion of metals. However, organic coatings are susceptible to defects and damages that may not be easily detected. If not repaired timely, these defects may develop into major coating failures due to corrosion occurring in the damaged region, thereby limiting the lifetime of the to be protected structure. Thus, the development of smart coatings that can accurately identify corrosion location and reliably recover the damage autonomously is of particular interest. Herein, we reported a robust, corrosion-sensing and self-healing coating which incorporated pH-sensitive ZIF-8-capped CaCO3 microcontainers containing the healing agent tung oil (TO) and the corrosion indicator/inhibitor 1,10-phenanthrolin-5-amine (APhen). The spontaneous leakage of incorporated TO and APhen was restrained, and the release initiated when local pH variation occurred. The corrosion protection performance of the coatings implanted with different contents of smart microcontainers were evaluated. The intact epoxy coating containing 7.5 wt% of the microcontainers exhibited the best protection performance with low water absorption (0.65 wt%), low O2 permeability (0.21 × 10–15 cm3 cm cm−2 s−1 Pa−1), and a high storage modulus (3.0 GPa). Electrochemical impedance spectroscopy (EIS) measurements in 3.5 wt% NaCl solution demonstrated superior durability of the composite coating after self-healing. The immersion test and neutral salt spray test confirmed the coating can accurately report corrosion sites via coloration.

Research Progress of Self-Healing Thermal Barrier Coatings: A Review

Reliability and durability are two important performance indicators for thermal barrier coatings (TBCs). The reliability of TBCs usually includes high adhesive strength, low thermal conductivity and high thermal shock resistance. The high reliability of TBCs ensures basic usage requirements. Durability demands TBCs have a long service lifetime before their eventual failure. The lifetimes of TBCs under actual service conditions are strongly dependent on crack initiation and propagation. Controlling and delaying the dynamic process of crack initiation and propagation is a direct approach to prolonging the service lifetime of TBCs. Self-healing TBCs usually have the specific function of inhibiting crack propagation, and thus promote the self-healing process of TBCs. The research progress of self-healing TBCs was reviewed. Firstly, the concept of self-healing or self-healing materials is clarified. Secondly, the research progress about some self-healing ceramic materials as well as self-healing TBCs is reviewed. Based on the review, the micro-structure design, propagation patterns of the crack and self-healing mechanism are discussed systematically. Additionally, the future development trend of the self-healing TBCs is also overviewed in this paper.

Self-healing Coating by Using Pore of Porous Film Formed on Al Alloy Anodized and Effect of Pore-Widening Treatment on Corrosion Protection

Self-healing Coating by Using Pore of Porous Film Formed on Al Alloy Anodized and Effect of Pore-Widening Treatment on Corrosion Protection

Self-Healing Organic-Inorganic Coatings

Nowadays, steel and light alloys, such as aluminum, magnesium, and titanium, represent most of the primary components of metallic structures in many applications [...]

Multifunctional antifogging, self-cleaning, antibacterial, and self-healing coatings based on polyelectrolyte complexes

In this study, a multifunctional coating with antifogging, self-cleaning, antibacterial, and self-healing capabilities is developed based on polyelectrolyte complexes of polyethylenimine (PEI), phytic acid (PA), and Cu2+ (denoted as PEI-PA-Cu). The multifunctional PEI-PA-Cu coating with high transparency can be prepared by spraying, brushing, or other one-step deposition onto various substrates (e.g., polymeric substrates and glass slides). Such a coating shows an excellent antifogging effect in both high temperature (85 ℃) and cold environments (−20 ℃) and maintains stable antifogging performance after placing in ∼65 ℃ vapor for 9 h. In addition, the coating is superhydrophilic and allows for easy spreading of water to isolate the oily contaminants, realizing self-cleaning. Meanwhile, the coating possesses superior antibacterial capability against Escherichia coli and Staphylococcus aureus thanks to PEI with amino groups and Cu2+. Importantly, the PEI-PA-Cu coating can heal damages rapidly and repeatedly due to the presence of hydrogen bonds and electrostatic interactions, effectively prolonging the service life. This study provides a facile route to construct multifunctional superhydrophilic coatings with promising prospects in the field of personal protective, medical, and optical devices.

Benzotriazole corrosion inhibitor loaded nanocontainer based on g-C3N4 and hollow polyaniline spheres towards enhancing anticorrosion performance of waterborne epoxy coatings

Multi-dimensional composite nanocontainers provided an opportunity to prolong the service life of waterborne self-healing coatings through combining intelligent protection with physical barrier. Herein, we constructed a benzotriazole (BTA) corrosion inhibitor loaded nanocontainer with barrier/controlled release/corrosion inhibition properties by assembling graphitic (g)-C3N4 lamella, hollow polyaniline capsule and outer polydopamine wall. Hollow polyaniline and g-C3N4 lamella with adsorption properties provide effective space and sites for loading BTA corrosion inhibitor. Outer polydopamine wall can not only realize the controlled release of corrosion inhibitor, but also ensure the good compatibility between the composite container and the water-based epoxy resin. In addition, polydopamine (PDA) and polyaniline (PANI) as a container frame can also serve as active inhibitors after the release of corrosion inhibitor to enhance the self-healing protection effect of waterborne coatings. In comparative evaluation, the composite coatings containing BTA-loaded nanocontainers (0.5 wt.%) exhibit obviously physical barrier effect after soaking in 3.5 wt.% NaCl solution for 40 days, and maintains good protective performance after immersion for 80 days. Meanwhile, the artificial scratch experiment verified the effective self-repair protection of the composite container to the coating under the condition of damage. To be sure, it will provide an effective improvement idea for the long-term application of waterborne epoxy coating in marine environment.

Synthesis of pH sensitive microcapsules containing ZAPP, SAPP, and 8-HQ, and evaluation of their anti-corrosion performance, and mechanical enhancement of epoxy coating

Self-healing coatings containing microcapsules have a remarkable ability to preserve metal surfaces for a long time, which is why these smart coatings have received a lot of attention. In this study, pH-sensitive poly melamine-formaldehyde microcapsules were synthesized by in-situ polymerization and loaded into the epoxy coating. 8-HQ, ZAPP, and SAPP were used as inhibitors in the core of microcapsules (named MF8HQ, MFZAPP, and MFSAPP, respectively). The microcapsules were synthesized at different stirring times and rates to obtain the optimum state (800 rpm and 2.5 h), then characterized by SEM, TEM, and FT-IR tests. Also, the mechanical properties of coatings with different weight percentages of loaded microcapsules were investigated using tensile measurement, DMTA, and Pull-off tests. The results revealed that the presence of 5 wt% of microcapsules in coatings is along with more appropriate Tg, modulus, and adhesion strength compared to more or fewer amounts. Also, EIS and salt spray tests were used to evaluate the anti-corrosion properties of the coating. The results suggested that epoxy coating containing MF8HQ showed the best anti-corrosion performance after 35 days of immersion in 3.5 wt% of NaCl solution (delamination index = 45.7 %), followed by MFZAPP (delamination index = 69.5 %) and MFSAPP performance (delamination index = 84.2 %) which were better than neat epoxy, respectively. Finally, the Quantum analysis was used to ensure the 8-HQ inhibitory performance and analyze the mechanism of inhibiting action at the interface.

Corrosion inhibition performance of polyolefin smart self-healing composite coatings modified with ZnO@β-Cyclodextrin hybrid particles

Corrosion is a global problem that results in substantial economic loss and is life-threatening as well. Currently, the utilization of self-healing coatings involving smart carriers encapsulated with the appropriate self-healing agents is a topic of great interest. Following this strategy, our work reports the synergistic corrosion inhibition performance of polyolefin-based smart coatings containing modified hybrid-based particles. The hybrid particles (ZnO@β-CD) comprising zinc oxide (ZnO) and β-Cyclodextrin (β-CD) were synthesized and modified with 2-mercaptobenzothiazole (2-MBT). The synthesized unmodified and modified hybrid particles were characterized by numerous techniques. TGA analysis confirmed that 2MBT was effectively loaded into ZnO@β-CD with almost 43% loading. UV-vis spectroscopic analysis results suggested that the self-release behavior of 2MBT is more pronounced in the acidic environment compared to the basic and neutral environment due to the dissociation of ZnO in the acidic environment. In the next stage, the synthesized unmodified (ZnO@β-CD) and modified (ZnO@β-CD-2MBT) hybrid particles were reinforced into a polyolefin matrix, followed by its application on steel substrate via dip-coating technique to formulate smart composite coatings. The Electrochemical impedance spectroscopy (EIS) results conducted on the developed smart composite coatings demonstrated that polyolefin coatings reinforced with modified hybrid particles (ZnO@β-CD-2MBT) displayed improved corrosion inhibition performance (98 GΩ cm2) as compared to the composite coatings (87 GΩ cm2) containing unmodified particles ((ZnO@β-CD) in 0.56 M NaCl solution after 20 days of immersion. This decent improvement in corrosion resistance behavior is attributed to the synergistic corrosion inhibition effect experienced due to the combined corrosion inhibition effect of ZnO and 2MBT.

Investigating local corrosion processes of magnesium alloys with scanning probe electrochemical techniques: A review

The study of corrosion of magnesium and its alloys has emerged a hot topic in the applications of lightweight structural materials. The inherently high electrochemical activity of bare magnesium surfaces still lacks a convincing mechanism to describe the observed experimental characteristics, and it has prompted the development of various types of protective coatings with the aim of slowing metal dissolution. In recent years, new instruments and techniques have been developed to study with spatial resolution the local corrosion processes that occur in metallic materials in general, and for magnesium and its alloys in particular, both for bare surfaces and coated. Scanning microelectrochemical techniques, such as local electrochemical impedance spectroscopy (LEIS), scanning electrochemical microscopy (SECM), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET) and scanning Kelvin probe (SKP) can provide information about the local electrochemical activity of metallic surfaces. In the present work, the applications of these techniques in corrosion studies of magnesium and its alloys are reviewed. Assessment of corrosion mechanisms, barrier properties of conventional coatings and active corrosion behavior of self-healing coatings are examined. Limitations and future developments in this area are discussed.

Formation of self-healing PEO coatings on AM50 Mg by in-situ incorporation of zeolite micro-container

Ce3+ ions containing zeolite microparticles were in-situ incorporated into plasma electrolytic oxidation (PEO) coating to provide self-healing property for AM50 Mg alloy. It was found that the Ce3+ ions can be released from the inertly incorporated zeolite microparticles via ion-exchange as well as from dissolved coating material which contains high concentration of reactively incorporated zeolites when corrosion occurs, leading to improved corrosion resistance of the oxide layer in 0.5 wt% NaCl solution. The newly formed cerium hydroxides/oxides when corrosion occurs can stabilize and enhance the barrier property of the passive film at metal/coating interface.

Self-healing nanocomposite coatings containing organic-inorganic inhibitors functionalized dendritic silica nanocontainers for synergistic corrosion protection of carbon steel

Corrosion inhibitors are crucial for self-healing of the coatings. However, the corrosion inhibition effect of single inhibitor is still limited. In this work, the self-healing nanocomposite coatings (HZK/EP) were prepared based on the synergistic effect of L-histidine (L-His) and Zn2+ ions. Dendritic silica (KCC-1) is used as nanocontainers to realize effective loading and release of inhibitors, thereby greatly improving anticorrosion ability of EP compared with the direct addition of inhibitors. Electrochemical impedance spectroscopy (EIS) results show that HZK/EP has a high |Z|0.01 Hz value of 3.32 × 1010 Ω·cm2 after 40 days of immersion in 3.5 wt% NaCl solution. His-Zn/KCC-1 endows epoxy coating with the excellent self-healing performance, which can be attributed to the fact that the lone pair electrons of N or O atoms of L-His can coordinate with the empty orbital of Zn2+ ions to form a complex.

Metal-Free, Low-Surface Energy, and Self-Healing Polyurethane Coating with an Excellent Antifouling Property

Metal-Free, Low-Surface Energy, and Self-Healing Polyurethane Coating with an Excellent Antifouling Property

Fabrication of mechanically robust urushiol-based polymer coatings with excellent self-healing property and hydrophobicity

It is of great significance yet challenging to develop functional polymer coatings possessing highly efficient self-healing performances and robust mechanical properties simultaneously. To this end, a novel strategy was proposed for the fabrication of self-healing urushiol-based coatings based on Diels-Alder (DA) bond. Natural urushiol was firstly modified by using epichlorohydrin and furfuryl alcohol, and then crosslinked by N,N′-(4,4′-methylenediphenyl) dimaleimide (BMI) via DA bond to obtain the thermally reversible and self-healing bio-based coating. The synthesized products were characterized, and their thermostabilities, physico-mechanical properties, thermal reversible and self-healing performances were investigated in detail. The results showed that the ratio of urushiol furan derivative to bismaleimide had a significant effect on the studied properties of the self-healing coatings. The self-healing efficiency, hardness, contact angle of the as-prepared coating after formulation optimization can reach 83.22 %, 5H and 109.6°, respectively. This work suggested that natural urushiol was a kind of potential excellent raw material for preparing self-healing coating, and also provided a simple and efficient way to fabricate bio-based self-healing coatings with robust hardness and good hydrophobic characteristic.

Self-Healing Coating with a Controllable Release of Corrosion Inhibitors by Using Multifunctional Zinc Oxide Quantum Dots as Valves.

As an intelligent response system, self-healing anticorrosion materials containing nanocontainers have aroused increasing demands. It is highly expected that the nanocontainers can rapidly respond on corrosion signals to efficiently release corrosion inhibitors, meanwhile to avoid an undesirable leakage before the local corrosion happening. Herein, zinc oxide quantum dot (ZnO-QD)-sealed hollow mesoporous TiO2 nanocontainers loading with 14.2% benzotriazole (BTA) inhibitor have been successfully prepared [hollow mesoporous titanium dioxide nanospheres (HMTNs)-BTA@ZnO-QDs]. ZnO-QDs play the multifunctional roles on anticorrosion of the self-healing coating. The corrosion tests of coatings on the carbon steel well demonstrate that ZnO-QDs can not only act as a valve to seal and release BTA on the time but also act as a precursor to produce the protective film of Zn(OH)2 by the reaction of Zn2+ ions with OH- around the cathode region to inhibit the corrosion of carbon steel. After being soaked in 3.5% NaCl solution for 30 days, the |Z|0.01Hz value of the coating with HMTNs-BTA@ZnO-QDs still maintains at 2.87 × 107 Ω cm2. Once the defects are formed in the coating, the acid-responsive ZnO-QD valves are rapidly decomposed to release BTA inhibitor; meanwhile, the resulted Zn(OH)2 layer prevent the carbon steel substrate from corrosion in the cathode area. Therefore, it could be promising that the present design of the nanocontainers matching with the multifunctional ZnO-QDs can offer a valuable strategy to construct the self-healing and anticorrosion coatings with a multiresponse to the corrosion environment.

Binary Sacrificial Coatings for Internal Corrosion Protection of Natural Gas Transmission Pipelines

One of the top reasons for the leaks in natural gas transmission pipelines is related to the internal corrosion of steel pipelines, mainly due to the presence of incidental H2O and CO2 in the line. Adding a protective coating or liner to the inner pipe surface reduces internal corrosion; however, conventional coatings (e.g., paint, epoxy, polyethylene, etc.) are insufficient to provide long-term corrosion resistance due to the permeation of the corrosive species such as H2O, CO2, Cl-. This research aimed to investigate the corrosion behavior of binary sacrificial coating for the protection of pipeline steel in a CO2-saturated aqueous electrolyte under natural gas pipeline conditions.Two types of the cold spray binary metallic coatings (ZnCr, ZnNb) were studied using electrochemical techniques: potentiodynamic polarization (PDP), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). The evaluation of the corrosion resistance of cold spray binary metallic coatings (ZnCr, ZnNb) was carried out in an environment containing 3 barg CO2 pressure, simulating the partial pressures that are found in gas transmission over a solution of 3.5 wt.% NaCl heated to 40 ºC. Post-corrosion surface characterization was performed using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS).The EDS mapping analysis and XRD results revealed the presence of ZnCO3 layer. EDS analysis showed that no Cr was detected on the surface of ZnCr coating after 24 hours of exposure. This may be due to a thick layer of ZnCO3 formed on top of the ZnCr coating. The obtained data showed that cold spray binary metallic coatings (ZnCr, ZnNb) can be used as sacrificial anodic materials to protect the interior of the steel pipeline against CO2 corrosion in a natural gas transmission environment. Furthermore, self-healing properties of the binary metallic coatings were demonstrated as protective corrosion products formed on the damaged regions of the coating.Keywords : CO2 corrosion, natural gas pipelines, cold spray coatings, zinc alloy, sacrificial coatings, self-healing coatings, electrochemical reaction autoclave

Dual pH-Sensitive Smart Coatings for Corrosion Inhibition of AA2024-T3

Aluminum alloys (AAs) have been broadly used in numerous applications due to their exceptional mechanical properties. Although AAs also exhibit outstanding resistance to general corrosion, they suffer from localized corrosion, such as pitting and crevice corrosion, and can therefore lead to unforeseen catastrophic failure. pH-sensitive smart coatings have been considered to be a promising strategy of combating the localized corrosion of AAs due to the unique self-healing capabilities. These smart coatings can sense the local pH decreases and increases induced by the anodic and cathodic reactions of AAs, respectively, thereby releasing corrosion mediating agents to the actively corroding sites on demand. However, the majority of smart coatings developed to date can only sense either acidic or alkaline condition, but not both. In this study, smart coatings that can respond to both acidic and alkaline environments are developed. These dual-pH sensitive smart coatings are based on weak polyelectrolyte coacervates consisting of polyacrylic acid and polyethylenimine or chitosan. When corrosion inhibitors such as SrCrO4 or Ce(NO3)3 are dispersed in these coatings and subsequently immersed in aqueous solutions with different pH values, the release rates of corrosion inhibitors are much higher in the acidic and alkaline environments than that of the neutral environment. Deposition of these inhibitor-loaded smart coatings on AA2024-T3 substrates leads to a significant improvement of the corrosion resistance. Furthermore, corrosion inhibitors are also encapsulated into the core-shell particles and nanofibers through the co-axial electrospray and electrospinning techniques, respectively. The shells of the particles and nanofibers are made from the polyelectrolyte coacervates, so they are dual-pH sensitive. These particles and nanofibers are sandwiched in an organic coating matrix and applied on the AA2024-T3 substrates, forming self-healing smart coatings with substantially improved corrosion resistance as evidenced by the electrochemical impedance spectroscopy analysis. In particular, the nanofibers embedded smart coatings can repeatedly heal the intentionally scribed area of the coated AA2024-T3 owing to the transport of corrosion inhibitors from remote areas through the nanochannels created in core-shell nanofibers.