Self-healing Anticorrosion Research Articles

Synthesis of Polyurethane/Poly(urea-formaldehyde) Double-shelled Microcapsules for Self-healing Anticorrosion Coatings

One-component, catalyst-free self-healing coatings with double-shelled polymer microcapsules have drawn considerable attention due to wide applications. In this work, the synthesis parameters of double-shelled polymer microcapsules and the mechanism of the self-healing process were systematically investigated. Apart from the chemical structure of the microcapsule shell, the shell thickness, the microcapsule size, and the core fraction could affect the self-healing anticorrosion properties. The synthesis parameters were further optimized in terms of the agitation rate, pH, weight ratio of core to shell, and temperature. Under these conditions, the microcapsule shell consisting of a rough surface formed by poly(urea-formaldehyde) and a smooth inner wall by polyurethane was prepared. The size of the microcapsules and core fraction were calculated to be approximately 30 μm and 75%, respectively. The self-healing anticorrosion coating incorporating as-synthesized microcapsules exhibited corrosion resistance in artificially scratched areas, which was further characterized by electrochemical impedance spectroscopy.

Hydrophobic self-healing polymer coatings from carboxylic acid- and fluorine-containing polymer nanocontainers

The development of multifunctional nanocontainers for self-healing coatings is of great interest for environmental and healthcare applications. In this study, we developed a synthetic strategy for a hydrophobic and self-healing anticorrosion coating from carboxylic acid- and fluorine-containing nanocontainers. Initially, well-defined poly (acrylic acid-co-trifluoroethyl methacrylate) microspheres were synthesized with different crosslinking agents by precipitation polymerization. The carboxylic acid groups allow for pH-responsive function to control the release of the encapsulated healing inhibitor to the cracks of polymer coatings on metal surfaces. The fluorinated groups of the polymer nanocontainers can endow the coatings with hydrophobicity. The as-synthesized multifunctional nanocontainers were further doped into the polymer coatings to generate self-healing coatings. The self-healing polymer coatings exhibited good crack inhibition since the inhibitor benzotriazole in pH-responsive nanocontainers can autonomously form new nanobarriers on metal surfaces around cracks after corrosion occurs. Furthermore, due to the micro/nanostructures of hydrophobic microspheres in the polymer coatings, the self-healing coating also exhibited good water resistance. The hydrophobic self-healing polymer coatings from the as-synthesized carboxylic acid- and fluorine-containing nanocontainers for anticorrosion were analyzed by electrochemical impedance spectroscopy (EIS).

Triple-Stimuli-Responsive Smart Nanocontainers Enhanced Self-Healing Anticorrosion Coatings for Protection of Aluminum Alloy.

Novel acid/alkali/corrosion potential triple-stimuli-responsive smart nanocontainers (TSR-SNs) were successfully assembled to regulate the release of an encapsulated corrosion inhibitor, benzotriazole (BTA), by installing specially structured bistable pseudorotaxanes as supramolecular nanovalves onto orifices of mesoporous silica nanoparticles. In normal conditions, BTA molecules were sealed in the mesopores. Upon any stimulus of acid, alkali, or corrosion potential, BTA molecules were quickly released because of the open states of the supramolecular nanovalves. TSR-SNs as smart nanocontainers were added into the SiO2-ZrO2 sol-gel coating to fabricate a stimuli-feedback, corrosion-compensating self-healing anticorrosion coating (SF-SHAC). Compared with the conventional pH-responsive smart nanocontainers synthesized for the SHAC, TSR-SNs not only respond to the pH changes occurring on corrosive microregions but also, and more importantly, feel the corrosion potential of aluminum alloys and give quick feedback. This design avoids wasting smart nanocontainers because of the local-dependent, gradient pH stimulus intensities and obviously enhances the response sensitivity of the SF-SHAC. Electrochemical impedance spectroscopy and salt spray tests prove the excellent physical barrier of the SF-SHAC. Through scanning vibrating electrode technique measurements, the SF-SHAC doped with TSR-SNs demonstrates inhibiting rates for corrosive microcathodic/anodic current densities that are faster than other control SHACs. The new incorporated corrosion potential-responsive function ensures the efficient working efficiency of TSR-SNs and makes full use of the preloaded corrosion inhibitors as repair factors.

Novel dual-functional coating with underwater self-healing and anti-protein-fouling properties by combining two kinds of microcapsules and a zwitterionic copolymer

Antibiofouling and repairing of the micro-cracked coating on the surface of the facilities in underwater environment are two great challenges in marine industries. This paper prepared a dual-functional coating with underwater self-healing and anti-protein-fouling properties by combining two kinds of microcapsules and a zwitterionic copolymer. First, epoxy resin microcapsules and underwater epoxy hardener microcapsules were prepared. Epoxy resin microcapsules with a poly(urea-formaldehyde) shell and the entrapped mixture of epoxy resin and n-butyl glycidyl ether showed homogeneous spherical morphology with encapsulation ratio of 90.42%. Underwater epoxy hardener microcapsules with a polymethyl methacrylate shell and the entrapped underwater epoxy hardener showed cellular spherical morphology with encapsulation ratio of 78.67%. Both of the microcapsules exhibited pretty thermal stability and acid, alkali and salt resistance. Then, two types of microcapsules were mixed with amine cured epoxy coating system to cast film on steel piece, and subsequently a zwitterionic polymer, ploy(sulfobetaine methacrylate-co-glycidyl methacrylate)(PSG) solution was casted on the surface of the un-cured epoxy coating. Therefore, a dual-functional coating with underwater self-healing and antibiofouling functions was obtained. The self-healing anticorrosion function attributed to the dual microcapsules and the anti-protein-fouling performance provided by PSG layer had been certificated. The facile combination of underwater self-healing and anti-protein-fouling functions may provide a new protection strategy for marine and other underwater facilities.

PH-responsive self-healing anticorrosion coatings based on benzotriazole-containing zeolitic imidazole framework

Utilization of self-healing nanocontainers with corrosion inhibitors is an efficient strategy for protecting metals from corrosion. However, self-healing coatings require the rapid release of these corrosion inhibitors to achieve an on-demand barrier on metal surface while avoiding unwanted leakage before the protective coatings are damaged. Herein, well-defined ZIF-7@BTA nanoparticles with approximately 30 wt% benzotriazole inhibitors are prepared via a ligand exchange approach. The as-synthesized ZIF-7@BTA nanoparticles can rapidly release the BTA inhibitor onto scratched areas on metal surfaces, providing 99.4% inhibition efficiency under acidic conditions. Moreover, only limited inhibitor of BTA molecules was leached out (less than 4%) in a neutral environment. Furthermore, the ZIF-7@BTA nanoparticles were further distributed in the polymer matrix to prepare the self-healing anticorrosion coatings for corrosion resistance enhancement in an acidic environment. Electrochemical impedance spectroscopy (EIS) analysis was utilized to characterize the corrosion resistance.

Efficient Graphene/Cyclodextrin-Based Nanocontainer: Synthesis and Host-Guest Inclusion for Self-Healing Anticorrosion Application.

Cyclodextrin, with a hydrophobic inner cavity and a hydrophilic exterior, is often used to encapsulate a widest range of guest molecules based on host-guest inclusion interactions. Graphene, an emerging nanobuilding material, exhibits great potential for numerous applications because of its superior characteristics. Herein, we synthesized a novel graphene/β-cyclodextrin-based supramolecular nanocontainer with excellent inhibitor encapsulating capacity and high impermeable properties. The benzotriazole (BTA)-loaded nanocontainers were then used to endow coating system with excellent passive and active anticorrosion performance. Local electrochemical impedance spectroscopy (LEIS) was performed to characterize the self-healing behavior of composite coatings. Results indicated that the protective capability of the scratched coatings can be recovered through BTA release from containers. Furthermore, the long-term corrosion resistance of container-based coating was largely improved as observed from EIS. The effective healing process involves two conditions: (1) the release of BTA from containers and formation of adsorption layers on exposed metal surfaces and (2) the impermeable graphene nanosheets greatly impeded the electrolyte penetration and corrosion extension around the scratch. This novel graphene/β-cyclodextrin-based nanocontainer endows polymer coating with efficient self-healing functionality and durable anticorrosion property.

PH-Responsive zeolitic imidazole framework nanoparticles with high active inhibitor content for self-healing anticorrosion coatings

Zeolitic imidazole framework (ZIF) is an emerging class of functional materials with promising nanostructures and applications in biomedicine and materials science. Herein we present a dynamic protective coating system with self-healing anticorrosion function, based on pH-responsive ZIF nanoparticles. Due to the advantage of high content of corrosion inhibitor in the ZIF-7 nanoparticles and its nature of pH-sensitivity, the ZIF-7 nanoparticles could quickly respond to the surrounding acid environment and release the linker as healing agent, led to a new barrier on scratched metal surfaces. The embedding and homogeneous distribution of the ZIF-7 nanoparticles in polymer coating system improved the corrosion resistance of carbon steel in 0.1 M hydrochloric acid solution in comparison to the control samples, as determined by electrochemical impedance spectroscopy (EIS). The self-healing anticorrosion property of dynamic polymer system was characterized during a simulated corrosion process by scanning electrochemical microscopy (SECM). The concentration of the embedded ZIF-7 nanoparticles was varied (0.5 − 7 wt %) to ascertain the optimum conditions for anticorrosion performance. The important effect of particle size and shape of ZIF-7 nanoparticles is discussed as well. The ZIF-7 based on dynamic protective polymer systems can interact with and adapt to the surrounding acid environment, leading to a new healed barrier on metal surfaces with anticorrosion functions.

High-efficiency self-repairing anticorrosion coatings with controlled assembly microcapsules

Based on the principle of emulsion technology and self-assembly of materials, aromatic isocyanate derivatives easily reacted with polyols to form polyurethanes, and nonaromatic isocyanate derivatives were responsible for generating the capsule core of the self-healing microcapsules. In this paper, epoxy resin-based self-healing smart anticorrosion coatings with different types of microcapsules were prepared. The cores were IPDI/TMP–IPDI/DiPE–IPDI. The optimal conditions for the preparation of self-repairing microcapsules to achieve controlled assembly of a microcapsule material structure were determined. We set up a test model, incorporating thermal analysis, depression repair level calculation, salt spray corrosion tests, adhesion tests, and other indicators of application performance. The corrosion resistance was in the order: DiPE–IPDI > TMP–IPDI > IPDI > pure epoxy. The experimental results showed a self-healing efficiency of more than 80% for cores of DiPE–IPDI. Taking into account the overall properties, the best-quality coatings contained approximately 5% microcapsules of DiPE–IPDI.

Chemically and thermally stable isocyanate microcapsules having good self-healing and self-lubricating performances

A new approach was developed to load 4,4′-bis-methylene cyclohexane diisocyanate in microcapsules, with outstanding stability in thermal and chemical environments, and excellent efficiency for both self-healing and self-lubricating uses. Well-dispersed microcapsules with diameter of 80 ± 22 µm and shell thickness of 3.8 ± 0.2 µm were produced with a core fraction of 74 ± 1.3 wt% as determined by titration. In thermal environments, the microcapsules started to lose 5% mass at 230 °C, which was higher than the boiling point of pure HMDI and thermal decomposition temperature of shell material. In chemical environments (hexane, xylene, ethyl acetate and water), the impermeable microcapsules reserved more than 90% of original core material after 20 days immersion. More interestingly, final microcapsules survived successfully in acetone losing only 25% of core material after 24 h. Parameters including microcapsules size, concentrations, immersion durations and solvent polarity were investigated systematically to obtain the stability of microcapsules in organic solvents. The smart coatings (10 wt% microcapsules) showed outstanding self-healing anticorrosion efficiency in sodium chloride solutions, and their friction coefficient decreased by 80% than control samples.

An Active Corrosion Inhibition Coating of Two Pack Epoxy Polyamide System using Halloysite Nanocontainer

This work deals with encapsulation of corrosion inhibitor in inorganic nanocontainer and the investigation of the corrosion inhibition rate from the nanocontainer. Halloysite nanotubes were used as inorganic nanocontainer for encapsulating the active corrosion inhibitor. These cylindrical shaped halloysite nanotubes are a natural aluminosilicate, which possesses similar chemical composition as that of pure kaolin clay. The structural morphology and functional organic attachments to the halloysite nanocontainers were determined by using TEM and FTIR analysis. It is found that, halloysite nanocontainers are having external and internal lumen is in nanosize (diameter) and length up to several micrometers. A maximum benzotriazole loading up to 10% (by weight) was achieved in inorganic nanotube of 50 nm external diameters and lumen of 15 nm. The release of corrosion inhibitor was carried out for 18 h at different pH ranging from 3 to 10. The weight percent of the benzotriazole encapsulated halloysite nanocontainer was varied from 2 to 10 and then dispersed in 2K clear coat epoxy-polyamide. The self-healing anticorrosion performance of these nanocomposites coating was tested with help of electrochemical impendence spectroscopy (EIS) and Tafel plot. From Tafel plots it is found that the Icorr value decreases to 1.018E–7A/cm2 from 0.018 A/cm2, when coating was applied with 2 wt % nanocontainer.

Novel self-healing anticorrosion coating based on L-valine and MBT-loaded halloysite nanotubes

This work creatively utilized the pH-dependent electrostatic interactions between L-valine (L-Val) and halloysite nanotubes (HNTs) to fabricate pH-responsive anticorrosion materials and compared with 2-mercaptobenzothiazole (MBT)-loaded HNTs, which were assembled via layer-by-layer (LbL) self-assembly. These two methods can achieve controlled release of inhibitors and self-healing performance. However, the loading capacity of L-Val-loaded HNTs is higher than that of MBT’s. There are 12 and 7 wt%, respectively. The pH-responsive release property was systematically evaluated by ultraviolet–visible (UV/Vis) spectrophotometry measurement. It demonstrates that 98% of adsorbed L-Val molecules released from HNTs within 300 min at pH 10 while the loaded MBT needs 120 h to achieve the equal ratio. Moreover, the difference of the release rate has a significant impact on the artificial crossed scratch experiment and shows a great performance gap in photographs. By comparing electrochemical impedance spectroscopy (EIS) data of three epoxy coatings, it can be seen that the epoxy coating, which was mixed with L-Val-loaded HNTs, shows a better anticorrosion ability than the epoxy coating contains MBT-loaded HNTs after immersion in 3.5 wt% sodium chloride solution for 96 h. Crucially, the pH-responsive anticorrosion material we fabricated can offer a rapid self-healing performance when the coating damaged by mechanical scratch via visual test and atomic absorption spectroscopy.

Self-healing active anticorrosion coatings with polyaniline/cerium nitrate hollow microspheres

Polyaniline (PANI) hollow microspheres have been synthesized by self-assembly method and doped with Poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and Ce ions. PANI/Ce(NO3)3 hollow microspheres of large specific area (10.9m2/g) and ultrahigh electrical conductivity (46.8S/cm) were applied as additives and dispersed in epoxy coating. EIS and Tafel polarization tests indicated that PANI/Ce(NO3)3 coating exhibiting excellent anticorrosion performance. Raman spectra revealed that compact and thin Fe3O4 layer has been formed on steel surface to block aggressive electrolytes. In addition, Ce ions promoted the formation of passivation layer and assured protection against corrosion without toxic inhibitor.

Furan-functionalized aniline trimer based self-healing polymers exhibiting high efficiency of anticorrosion

An aniline trimer derivative possessing multiple furan groups (TFAT) is prepared and used as a building unit for preparation of self-healing anticorrosion coatings. The aniline trimer unit brings electrochemical activity to TFAT, and the tertiary amine and glycidylether groups provide TFAT excellent adhesive ability. Both features contribute to the high performance of anticorrosion property of crosslinked TFAT coatings on cold-rolled steel (CRS). An ultralow corrosion rate of 0.12 μm y−1 and a high impedance at low frequency (Z0) of 9.2 × 105 Ω cm−2 have been recorded with the coatings, both demonstrate hundreds times enhancements of the anticorrosion properties compared to the CRS samples coated with crosslinked aniline trimer (corrosion rate: 71 μm y−1; Z0: 1240 Ω cm−2). Moreover, as possessing furan groups, TFAT is a suitable agent to react with multifunctional maleimide compounds for formation of thermally-reversible crosslinked networks through Diels-Alder reaction. Consequently, TFAT-based self-healing anticorrosion coatings are obtained. In a cycle test, the TFAT-based reversible crosslinked coating demonstrates a high self-healing efficiency of anticorrosion with a recovery of protection efficiency from 79.8% to 99.2%, corresponding to a 99.3% of protection efficiency based recovery. A new material showing high anticorrosion and self-healing efficiency for self-healing anticorrosion coatings has been demonstrated.

Green synthesis of nanocapsules for self-healing anticorrosion coating using ultrasound-assisted approach

AbstractThe present work deals with the production of nanocapsules containing a natural corrosion inhibition component.Azadirachta indica wasencapsulated in urea-formaldehyde polymeric shell using ultrasound-assisted and conventional approaches of in situ polymerization. Subsequently nanocapsules were incorporated into clear epoxy polyamide to develop the green self-healing corrosion inhibition coating. The actual performance of the coating was evaluated based on the studies involving the repair of the crack of high solid surface coating. Corrosion inhibition of the healed area has been evaluated using the electrochemical impedance spectroscopy and immersion test based on the use of standard epoxy coating. The obtained results confirmed better corrosion protection in terms of the electrochemical impendence spectroscopy data and Tafel plot. It was found that current density decreases from 0.0011 A/cm2(for standard epoxy coating) to 5.22 E−7A/cm2as 4 wt% nanocapsules incorporated in coating.

Self-healing Anticorrosion Coatings for Gas Pipelines and Storage Tanks

In the present study, chitosan based self-healing anticorrosion coatings were prepared by layer by layer (lbl) addition of chitosan (Ch) and polyvinyl butyral (PVB) on mild carbon steel substrate. Chitosan coatings exhibited enhanced coating stability and corrosion resistance in aggressive environments by the application of a PVB top layer. Chitosan layer in the lbl coatings have been modified by using glutaraldehyde (Glu) and silica (<TEX>$SiO_2$</TEX>). Performance of different coatings was tested using electrochemical impedance spectroscopy and immersion test. The best anticorrosion performance was observed in case of 10 % Ch_<TEX>$SiO_2$</TEX>_PVB coatings, which withstand immersion test over 25 days in 0.5 M salt solution without visible corrosion. 10 % Ch_<TEX>$SiO_2$</TEX> coatings without the PVB top layer didn't last more than 3days. Application of PVB top layer sealed the defects in the chitosan pre-layer and improved its hydrophobic nature as well. Raman spectra and SEM of steel surfaces after corrosion study and removal of PVB_Ch/Glu_PVB coatings showed a passive layer of iron oxide, attributing to the self-healing nature of these coatings. Conducting particle like graphene reinforcement of chitosan in the lbl coatings enhanced corrosion resistance of chitosan coatings.

Anticorrosion behavior of cyclodextrins/inhibitor nanocapsule-based self-healing coatings

The self-healing anticorrosion property of coating containing cyclodextrins/inhibitor nanocontainers was investigated by SEM, TEM, salt spray, and EIS measurements. The influences of cyclodextrin type (α-CD, β-CD and γ-CD) and nanocapsules diameter on the anticorrosive performance of the scratched samples were studied under salt spray conditions, which revealed that the coatings containing γ-CD/inhibitor nanocontainers with larger nanocapsules at room temperature demonstrated the best anticorrosion behavior. Inclusion complex formation of MBI or MBT with CDs led to encapsulated corrosion inhibitors which became active in corrosive electrolytes, and could slowly diffuse out of the host material to ensure continuous delivery of the inhibitors to corrosion sites and long-term corrosion protection. Additionally, the kinetics of the self-healing process characterized by EIS measurement was parametrically analyzed in an equivalent circuit when the coating was exposed to salt solution.

Self-healing anticorrosion coating containing 2-mercaptobenzothiazole and 2-mercaptobenzimidazole nanocapsules

γ-cyclodextrin (γ-CD) inclusion complex containing 2-mercaptobenzothiazole (MBT) or 2-mercaptobenzimidazole (MBI) as guest was prepared by precipitation method at two conditions (at room temperature and under sonic energy). Supramolecular nanocontainers were characterized by 1H-NMR, XRD, SEM, DSC and FTIR, which proves the formation of the inclusion complex where the benzyl part of MBT or MBI has been encapsulated by the hydrophobic cavity of γ-CD. Differences between 1H-NMR, FTIR and XRD spectra of physical mixtures and inclusion complex indicated formation of MBT/γ-CD and MBI/γ-CD supramolecular nanocontainers in solid phase.

A reactive blend of electroactive polymers exhibiting synergistic effects on self-healing and anticorrosion properties

The first example of electrically-induced self-healing anticorrosion materials shows synergistic effects on anticorrosion efficiency and self-healing property.

Layer-by-Layer Assembly of a Self-Healing Anticorrosion Coating on Magnesium Alloys.

Fabrication of self-healing anticorrosion coatings has attracted attention as it has the ability to extend the service life and prevent the substrate from corrosive attack. However, a coating system with a rapid self-healing ability and an improved corrosion resistance is rarely reported. In this work, we developed a self-healing anticorrosion coating on a magnesium alloy (AZ31). The coating comprises a cerium-based conversion layer, a graphene oxide layer, and a branched poly(ethylene imine) (PEI)/poly(acrylic acid) (PAA) multilayer. We incorporated the graphene oxide as corrosion inhibitors and used the PEI/PAA multilayers to provide the self-healing ability to the coating systems. X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the composition of the multilayers, and scanning electron microscopy (SEM) was used to analyze the surface morphology. The electrochemical impedance spectroscopy (EIS) results illustrate the improved corrosion resistance of the coating. The proposed coating also has a rapid self-healing ability in the presence of water.

Advanced micro/nanocapsules for self-healing smart anticorrosion coatings

Smart self-healing micro/nanocontainers that heal cracks in the coating by releasing active compounds in response to external stimuli were reviewed.