Self-healing Anticorrosion Research Articles

Dynamic Polymer/Metal-Organic Framework Hybrid Microcapsules for Self-Healing Anticorrosion Coatings.

An ideal microcapsule effectively preserves an active substance and can rapidly release it to elicit a self-healing anticorrosion effect. However, the development of highly efficient microcapsules remains a challenge. In this study, polymer/metal-organic framework hybrid microcapsules with dynamic properties were constructed as self-healing anticorrosion coatings. The shell of the microcapsule consisted of flexible polydopamine and a hard crystalline zeolitic imidazolate framework-8 (ZIF-8) layer. The corrosion inhibitor 8-hydroxyquinoline (8-HQ) was trapped in the microcapsules and remained unreleased because the ZIF-8 layer acted as a molecular sieve. When the coating was surrounded by an acidic environment, the ZIF-8 nanocrystals in the shell dissociated, followed by the release of 8-HQ. A dense protective layer was formed on the steel surface to suppress extensive corrosion propagation. The |Z|0.01Hz value of the self-healing coating increased from 1.9 × 104 Ω cm2 to 2.2 × 106 Ω cm2 within 48 h and remained at this level until 120 h post application. This value is 3 orders of magnitude higher than that of a pure epoxy coating under the same conditions. Compared with conventional coatings, the novel dynamic microcapsules enable the application of self-healing coatings that can withstand harsh acidic environments without human intervention.

Unveiling the potential of dual-extrinsic/intrinsic self-healing lignin-based coatings for anticorrosion applications

The development of self-healing ecofriendly coatings for anticorrosion applications provides stronger protection than passive coatings and mitigates the environmental pollution resulting from petroleum-derived coatings. Due to its intrinsic anticorrosion characteristics, lignin is a viable precursor for the formulation of self-healing anticorrosion coatings. However, the structural rigidity of lignin and the lack of self-healing functionalities in pristine lignin-based coatings hinder the comprehensive application of lignin in this field. Accordingly, we introduced Diels-Alder (DA)-based self-healing functions in the lignin-based coatings and meanwhile, the coatings were chemically conjugated with corrosion inhibitors to further improve the anticorrosion performance. A thin layer (16 μm) of the coating increased the Ecorr from −481 mV (for bare steel) to +91 mV and reduced the corrosion rate (CR) >4000 times. The dual self-healing properties of the coating are attributed to the synergistic action of the DA adduct and the conjugated corrosion inhibitor. Practically, in response to the emergence of microcracks in the coating structure, trace amounts of the corrosion inhibitor are released into the microcracks to form a protective layer on the unveiled metal surface. Simultaneously, DA adducts undergo reversible reactions at specific temperatures (80–120 °C) promoting complete restoration of the microcrack.

Synthesis and application of Aromatic Schiff base waterborne polyurethane as visible-light triggered self-healing polymer and anticorrosion coating using h-BN/GO/NiO nano-composite

Herein, a self-healing waterborne polyurethane (WPU) based on a novel visible light-stimulated healing agent from the aromatic Schiff base family (SBWPU) was synthesized. Moreover, this polymer exhibited remarkable mechanical properties, making it an ideal matrix for the preparation of a new nano-composite coating using hexagonal-boron nitride/graphene oxide/nickel oxide (h-BN/GO/NiO) nano-composite for anti-corrosion applications. SBWPU containing 15 wt % of synthesized healing agent (SBWPU-15) demonstrated favorable healing properties (80.03 %) under a visible light lamp after 24 h (at ambient temperature). SBWPU containing 20 % of the healing agent (SBWPU-20) showed high mechanical properties (20.80 MPa) and an increase in its hydrophobic properties. Additionally, its water absorption rate decreased, making it an attractive option as a polymer matrix for anti-corrosion coating applications. The nano-composite coatings (CSBWPU) were formulated by introducing varying amounts of h-BN/GO/NiO into the SBWPU-20. The coatings displayed an increase in contact angle and a decrease in water absorption rate. The electrochemical impedance spectroscopy (EIS) results revealed that the 0.75-CSBWPU, containing 0.75 % nano-composite, had the highest corrosion resistance (1.58 × 1010 Ω cm2) after 90 days of immersion in seawater. This work offers a potentially helpful concept for developing an eco-friendly, secure, uncomplicated accessibility self-healing polymeric system with controllable mechanical features, which are also favorable for designing novel corrosion protection composite coatings.

Dual Anticorrosive and Self-healing Coating Based on Multiresponsive Polyaniline Porous Microspheres.

In this work, a smart self-healing coating with long-term anticorrosion ability was developed based on multiresponsive polyaniline (PANI) porous microspheres. The polyaniline porous microspheres loaded with corrosion inhibitor (benzotriazole, BTA) was prepared by the emulsion template method and photopolymerization. The BTA loaded in the polyaniline microspheres acted as a corrosion inhibitor, while the polyaniline in the shell performed the multiple functions of corrosion inhibition, pH-responsive and photoresponsive release, and photothermal conversion. Owing to the inherent corrosion-inhibiting nature of BTA and PANI, the BTA-loaded polyaniline microsphere could endow coating with dual anticorrosive properties. The coating with polyaniline microspheres did not show any corrosion product after 700 h of salt spray testing, while obvious pitting corrosion could be observed for the blank coating after 100 h of the salt spray test. Thanks to the photothermal properties of PANI, the composite coating exhibited self-healing behavior under NIR light irradiation. The coating with 10 wt % polyaniline microspheres could achieve rapid closure and recover its barrier properties within 5 s of NIR irradiation. And the release of BTA could form a passivation film on scratches to further repair coating defects. The on-command responsive release, high healing efficiency, and excellent anticorrosion properties of this dual self-healing anticorrosion coating provide perspectives on extending the service life of metals.

Janus GO/BTA/PMMA Microcapsules for Biobased Self-Healing Anticorrosion Coatings with Ultrahigh Performance.

The giant reduction of the barrier properties due to self-healing microcapsules and the lack of real-time protection during the healing remained the main challenges in self-healing anticorrosion coatings. Herein, a facile strategy using Janus graphene oxide (GO) as a dense and flexible shell has been proposed to synergistically solve these challenges. Benzotriazole (BTA) was used to synthesize Janus GO at the oil-water interface, and Janus GO/BTA/poly(methyl methacrylate) microcapsules were prepared. Energy-dispersive X-ray spectroscopy, Fourier infrared spectroscopy, Raman spectroscopy, and ultraviolet spectrophotometer analysis confirmed the formation of a Janus GO structure with one surface hydrophilic and the other hydrophobic. The surface morphology of J-GO-capsules with a high GO coverage rate was observed by scanning electron microscopy. The high biobased content coating containing J-GO-capsules showed a low-frequency impedance value above 1010 as assessed by electrochemical impedance spectroscopy after being immersed in 3.5 wt % NaCl solution for 60 days. In addition, the low-frequency impedance values of the coating were maintained after being scratched due to the self-healing properties of the J-GO-capsules as well as the real-time protective effect of the BTA. Biobased coatings with the best overall properties among all of the self-healing anticorrosion coatings were prepared.

Phytic acid-doped polypyrrole/graphene oxide nanofillers for the preparation of self-healing anticorrosion coatings with the synergistic physical barrier, passivation and chelating effect

The corrosion protection of organic coatings for metal substrates is generally limited because of the unavoidable coating micropores and cracks, even the coating anticorrosion function will lose when it is damaged. Although the addition of nanofillers into the organic coating matrix can effectively address the above issues, it is challenging to facilely and wholesale construct surface-modified nanofillers with synergistic anticorrosion ability of physical barrier, passivation and chelating effect. In this study, we develop a simple one-pot approach for preparing polypyrrole (PPy) modified graphene oxide (GO) nanofillers with the doping of phytic acid (Ph) (namely GO-PPy@Ph nanoparticles) and then incorporating them into epoxy resin (EP) coating system to form the anticorrosion nanocomposite coatings. The research results display that the GO-PPy@Ph nanoparticles can uniformly disperse in the EP coatings to improve their anti-penetrant ability against corrosive media. And the introduction of GO-PPy@Ph nanoparticles effectively enhances the coating adhesion strength and mechanical performance. Moreover, the anticorrosion tests show that the impedance modulus at 0.01 Hz of GO-PPy@Ph coating after 60-day immersion in 3.5 wt% NaCl solution remains at about 1010 Ω cm2. The dramatical anticorrosive performance of the GO-PPy@Ph coating with self-healing performance is attributed to the synergistic protection of impermeable GO-PPy@Ph nanosheets, passivation function of PPy and metal chelation effect of Ph. This study provides an effective and universal avenue to construct multifunctional nanofillers with the synergistic anticorrosion of high physical barrier, passivation and metal chelating effects for developing anticorrosive nanocomposite coatings with high performances, which have highly attractive potential in the commercialization applications of metal corrosion protection.

Preparation of Graphene Oxide/Polymer Hybrid Microcapsules via Photopolymerization for Double Self-Healing Anticorrosion Coatings.

In this work, graphene oxide (GO)/polymer hybrid microcapsule-loaded self-healing agents were prepared via the combination of the emulsion template method and photopolymerization technology. The incorporation of GO in the microcapsule shell not only improved the impermeability, mechanical property, and solvent resistance property of the microcapsules significantly but also endowed the microcapsules with photothermal conversion property. By incorporating GO/polymer hybrid microcapsules in water-borne epoxy resin, a novel kind of anticorrosion coating with a double self-healing property was successfully fabricated. When the coating was scratched, the linseed oil (LO) encapsulated in the microcapsules could fill the crack, and the photothermal conversion property of GO could promote the molecular chain movement of the damaged area under near-infrared (NIR) irradiation to realize the close of the crack. Based on the filling of LO and photothermal conversion-induced scratch narrowing, the "filling" and "close" double self-healing effect can be realized under temporal NIR irradiation, which could lead to the complete recovery of the scratched coating. The |Z|f=0.1Hz value of the damaged coating with GO/polymer microcapsules after double healing was comparable to that of the intact coating, which was about 4 orders of magnitude higher than that of the scratched blank coating and single self-healing coating. As to the neutral salt spray test, the scratched blank coating failed in protection after 100 h, while the healed composite coating did not show any corrosion after 300 h.

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.

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.

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.

Biohybrid microcapsules based on electrosprayed CS-immobilized nanoZrV for self-healing epoxy coating development.

In this work, zirconium vanadate nanoparticles were immobilized into chitosan using a facile electrospraying technique to produce CS-ZrV hybrid microcapsules for the development of a self-healing coating. Upon assessment, hybrid microcapsules possessed desirable properties with a mean particle size of 319 μm, maintaining good thermal stability of ∼55% at 700 °C, and were subsequently incorporated into an epoxy resin to develop a biocompatible self-healing coating, CZVEx, for carbon steel corrosion protection. Scratched samples of self-healing and control coatings were analyzed in a corrosion medium of 3.5 wt% aqueous NaCl. SEM images of the scratched coating sample, after days of immersion, revealed healing of defects through the appearance of an epoxide gel-like substance due to the release of polymeric vanadate that reacted with corrosion agents, resulting in polymerization of vanadium hydrates and subsequent self-healing, validated by the proposed mechanism of self-healing. Electrochemical impedance spectroscopy analysis further confirmed CZVEx coating possessed excellent self-healing capabilities through a significant impedance rise from 4.48 × 105 to 5.52 × 105 (ohm cm2) between the 7th and 14th day of immersion. Furthermore, comparative polarization assessment of coating samples with/without defects indicated the accuracy of EIS for self-healing analysis, and showed the sample with no defect was only 2.6 times more corrosion resistant than the scratched coating, as against bare steel substrate that was 22 times less resistant, revealing superior self-healing anticorrosion properties of the coating.

Design Polyaniline/α-Zirconium Phosphate Composites for Achieving Self-Healing Anti-Corrosion of Carbon Steel.

The rupture of a micro/nano container can trigger the release of repair agents and provides the coating with a self-healing and anti-corrosion effect. However, the defect and inhomogeneity of the coating, produced by the rupture of the micro/nano container, may weaken its anti-corrosion performance. This study reports a rare protection mechanism, which optimizes the space occupying of zirconium phosphate, and the de-doping peculiarity of polyaniline without the rupture of the micro/nano container. Polyaniline/α-zirconium phosphate composites were constructed through in situ oxidation polymerization. Repair agents were added in the form of doped acids. According to the different repair agents in polyaniline/α-zirconium phosphate composites (citric ion, tartaric ion and phytic ion), the performance and protection mechanism of the composites were researched. Polyaniline/α-zirconium phosphate coating (with phytic ion) shows an excellent self-healing anti-corrosive effect, due to the large spatial structure and abundant chelating groups of the precipitation inhibitor. Considering the anti-corrosive application, the developed polyaniline/α-zirconium phosphate composite has a far-reaching influence on marine development.

Blue-ringed Octopus inspired slippery coating with physico-chemical synergistic antifouling properties

Bionic superhydrophobic and slippery liquid-infused porous surfaces (SLIPS) have attracted great interest due to their antifouling properties, while the poor stability, complex preparation of porous structures and rapid loss of lubricants, as well as only possessing physical antifouling capability, have hindered their further application. Herein, inspired by the Blue-ringed Octopus’ defensive equipment of slippery skin and toxin secretion when faced with predators, an antifouling slippery coating containing repellent is easily prepared. The repellent capsaicin physically connected to the slippery networks can be activated to accelerate release in response to the changes in pH caused by bacterial secretions, and the adhesion resistance of the coating is improved by 99 % compared to aluminum plates, both conclusions confirmed by experimental and computational data. The anti-adhesive properties of the slippery surface, combined with the repellent properties of capsaicin provides the coating with excellent synergistic physico-chemical antifouling performance. This is demonstrated by the fact that the surface of the coating remains clear after contamination with proteins, bacteria and diatoms, as well as after 65 days of marine field testing. Additionally, the slippery surface has self-healing and outstanding anticorrosion ability. Therefore, the eco-friendly coating has promising application prospects in marine field for antifouling purposes.

Preparation and properties of MAO self-healing anticorrosion film on 5B70 Al alloy

Micro-arc oxidation (MAO) was a new surface treatment technology for Al alloys. However, the MAO ceramic film could not provide long-term protective performance owing to its inherent porous structure. In this work, a new type of CeO2-sealed GO/Al2O3 composite film on 5B70 Al alloy with excellent corrosion resistance was prepared by integrating MAO and the hole sealing technique. The experimental results indicated that the loose and porous MAO ceramic film could serve as a ‘shield’ and a ‘reservoir’, respectively, to obtain improved impedance and sufficient corrosion inhibitor loading. Compared to the original MAO ceramic film or GO/Al2O3 composite film, The GO/Al2O3 composite film after sealing treatment for 60 min had lower porosity and better corrosion resistance. In addition, CeO2-sealed GO/Al2O3 composite film exhibited a positive self-healing effect in 3.5 wt% NaCl solution.

In-situ self-crosslinking strategy for autonomous self-healing materials

Autonomous self-healing anticorrosion protective coatings from intrinsic polymers is a great challenge. In this work, in-situ self-crosslinking strategy was demonstrated for constructing self-healing anticorrosion polymers. The as-synthesized polymers had tunable catechol content and mechanical properties. The specimens could be repaired in an Fe3+ solution owing to the formation of dynamic catechol-Fe3+ coordination crosslinking sites. Moreover, when scratched, the prepared polymers exhibited a self-healing anticorrosion performance, as evidenced by salt immersion and electrochemical impedance spectroscopy. An in-situ self-crosslinking mechanism was proposed, which was derived from the dynamic coordination of catechol groups in the polymer chains and Fe3+ produced from the metal substrate. This intrinsic self-healing anticorrosion polymer are highly potential for anticorrosion applications in harsh environments.

A self-healing epoxy composite coating based on pH-responsive PCN-222 smart containers for long-term anticorrosion of aluminum alloy

A novel pH-responsive smart container system has been developed using the metal-organic framework PCN-222 for the purpose of self-healing anticorrosion coating on Al alloy. The inhibitors 8-hydroxyquinoline (8-HQ) incorporate with PCN-222 by binding tightly to Zr6 clusters and porphyrin of PCN-222 via hydrogen bonding and π-π stacking, ensuring high loading and pH-triggered release activity. Additionally, PCN-222 interacts covalently with epoxy resin, prompting the dispersion of 8-HQ@PCN-222 and crosslinking of the epoxy coating. The resulting 8HQ@PCN-222 composite provides good compatibility with epoxy resin and impressive self-healing performance, all of which contribute to the long-lasting anticorrosion ability of the composite coating.

Development of self-healing sol-gel anticorrosion coating with pH-responsive 1H-benzotriazole-inbuilt zeolitic imidazolate framework decorated with silica shell

Zeolitic imidazolate framework-8 (ZIF-8)-based pH-responsive nanocontainers present a new pathway to endowing sol-gel anticorrosion coatings with self-healing ability. The organic nature of the ZIF-8-based nanocontainers, however, makes them less compatible with the inorganic sol-gel coating matrix, thus ineffective in protection against corrosion. In this paper, a novel pH-responsive corrosion inhibitor release system (BTA-ZIF-8@SiO2) based on ZIF-8 for self-healing sol-gel anticorrosion coating was reported. A facile one-step self-assembly procedure was used to create the 1H-benzotriazole (BTA)-encapsulated ZIF-8 core, on which a layer of silica was subsequently coated using a standard sol-gel method. The silica shell can provide better compatibility of the nanocontainers with the sol-gel matrix, thus improving the overall corrosion protection. Characterizations of the BTA-ZIF-8@SiO2 nanocontainers via X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer−Emmett−Teller, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy confirmed the successful synthesis of ZIF-8-based nanocontainers with high loading content of BTA and mesoporous SiO2 shell. Inhibitor release studies revealed the pH-responsive smart release of inbuilt BTA at both acidic and alkaline media. The anticorrosion performance of sol-gel coating incorporating the nanocontainers was investigated by electrochemical impedance spectroscopy, scanning Kelvin probe, and salt spray test, and the results indicated that BTA-ZIF-8@SiO2 could effectively enhance the corrosion protection properties of the coating and exhibit excellent self-healing performance, in which the |Z|0.01Hz was >2 orders of magnitude higher and coating resistance and oxide layer resistance were >3 orders of magnitude higher than these of pure sol-gel coating after 28 d of immersion. This could be attributed to the synergistic effect of enhanced passive protection, improved nanocontainer compatibility with the sol-gel matrix, and corrosion inhibitor film formed on metal surface.

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 waterborne epoxy composite coatings with modified graphene oxide nanosheet supported zinc ion and its self-healing anticorrosion properties

In this study, a waterborne epoxy coating with the dual functions of self-healing and anti-corrosion was obtained through nanocomposites of (GO@(PDA + KH-550)-Zn). GO@(PDA + KH-550-Zn) was prepared by grafting dopamine (DA) with a silane coupling agent (KH-550) onto a graphene oxide (GO) backbone, and by then loading zinc ions to obtain modified GO nanocomposites. The GO modified through the formation of GO@(PDA + KH-550)-Zn was uniformly dispersed in the water-based epoxy coating. The results of anti-corrosion tests showed that the GO@(PDA + KH-550)-Zn/WEP composite coating recorded its highest impedance value of 2.14 × 109 Ω·cm2 after 26 days, where this was three orders of magnitude higher than that of a blank water-based epoxy coating (WEP). It still had a high impedance value of 8.71 × 108 Ω·cm2 after 32 days, with a rate of corrosion of 0.007 mm/year. The self-healing performance of the GO@(PDA + KH-550)-Zn/WEP composite coating containing scratches was verified by electrochemical impedance spectroscopy (EIS) tests. Scanning electron microscope (SEM) images showed that intermediate scratches on the GO@(PDA + KH-550)-Zn composite coating had been repaired, probably due to the release of a corrosion inhibitor (Zn) due to the peeling of the PDA from the surface of the GO. When the electrolyte penetrated into the coating, the release of zinc ions led to the formation of oxide films on the cracks, and the PDA was able to anchor ferrous or trivalent iron cations (Fe2+/Fe3+) to promote the adhesion and bonding of the composite coating by exerting a unique self-healing function.

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.