Self-healing epoxy coatings loaded with inhibitor-containing polyelectrolyte nanocapsules

The self-healing polymer coatings containing organic corrosion inhibitors are intensively investigated as an alternative for highly toxic Cr(VI)-based systems. Protective self-healing coatings are realized by embedding “smart” containers, able to release a corrosion inhibitor under some specific conditions occurring when the corrosion process starts (e.g. on pH change) or upon a mechanical damage. In this study a system with the corrosion inhibitors (2-methylbenzothiazole (BT) and 2-mercaptobenzothiazole (MBT)) encapsulated inside the polyelectrolyte nanocapsules embedded in the water-based epoxy coatings is tested for its self-healing performance. The nanocontainers were prepared by the electrostatic adsorption of polyelectrolytes directly on the oil phase drops containing the inhibiting agent. The results for BT emulsion droplets and the mixture of BT and MBT encapsulated by docusate sodium salt/poly(diallyldimethylammonium chloride) (AOT/PDADMAC) and docusate sodium salt/poly(diallyldimethylammonium chloride)/poly(styrene sulfonate) (AOT/PDADMAC/PSS) surface complexes are presented.The X-ray Photoelectron Spectroscopy (XPS) was used to confirm the release of the inhibitor from the scratched coating. The influence of the nanocapsules on the barrier properties and self-healing performance of the epoxy coatings were tested by electrochemical impedance spectroscopy (EIS) in NaCl solution, the salt spray test (SST) according to ISO9227 and filiform corrosion test (FFT) according to EN ISO 3665. Potential blistering was rated according to EN ISO 4628-2.     

Epoxy coating with self-healing capability based on a 2-mercaptobenzothiazole-loaded CeO2 nanocontainer

In this study, we demonstrated a facile approach for the synthesis of nanocontainers using the encapsulation of a 2-mercaptobenzothiazole (MBT) inhibitor; these nanocontainers were capable of responsively releasing a corrosion inhibitor and of self-healing performances. The anticorrosive performance of the CeO₂ nanocontainers was investigated with electrochemical impedance spectroscopy (EIS) measurement in a saline electrolyte via the incorporation of different weight percentages (0.5, 1, and 2 wt %) of synthesized nanocontainer in epoxy (EP) resin. The EIS results show that the loading of 1 wt % CeO₂ nanocontainer containing MBT inhibitor in the epoxy (EP) coating [EP/NC MBT–CeO₂ (1%)] provided the highest R_coat, the lowest constant phase element of coating, and the optimum release of MBT at different operating pHs. The highest coating resistance R_coat values of this coating (7.81 × 10⁷ Ω cm²) were about 12 and 8573 times greater than those considered for EP–CeO₂ and EP coatings, respectively. Different releases of the MBT inhibitor were detected at various pHs. We found that the coating operating in acidic media exhibited a better self-healing performance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47297.     

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.     

Anticorrosive behavior study by localized electrochemical techniques of sol–gel coatings loaded with smart nanocontainers

In the present work, sodium phosphomolybdate, an environmentally friendly corrosion inhibitor with good anticorrosive behavior when applied on steel substrates, has been loaded and encapsulated in mesoporous silica nanoparticles without and with a hollow core in order to produce different smart nanocontainers. These nanocontainers have been designed to allow controlled release of the inhibitor in response to an external stimulus, thereby achieving more efficient and more economical use of the active substance. Corrosion activity leads to local changes in pH, and this work considers such changes as a signal of great interest. The nanocontainers respond to a pH of 10 or higher by increasing the release rate of the encapsulated active material. The smart nanocontainers have been incorporated into hybrid organic–inorganic sol–gel coatings and applied on carbon steel substrates. Mechanical defects have been made in the organic coating, reaching through to the metallic substrate, in order to study anticorrosive behavior in the affected area. A characterization study has been carried out at the defects and in their surroundings by means of two different localized electrochemical techniques: Scanning Kelvin Probe and Localized Electrochemical Impedance Spectroscopy. The results have shown significant improvement in the anticorrosive behavior of sol–gel coatings when formulated with smart nanocontainers loaded with sodium phosphomolybdate compared to a reference sol–gel coating.     

Improvement of anti-corrosive properties of epoxy-coated AA 2024-T3 with TiO2 nanocontainers loaded with 8-hydroxyquinoline

Epoxy coatings containing TiO₂ nanocontainers were applied on aluminium alloy (AA) 2024-T3 for corrosion protection. The nanocontainers were loaded with the corrosion inhibitor 8-hydroxyquinoline (8-HQ). Epoxy coatings were deposited via the dip-coating process. The morphology of the coatings was examined by scanning electron microscopy (SEM). The composition of the films was determined by energy dispersive X-ray analysis (EDX). Electrochemical impedance spectroscopy (EIS) was employed for the characterization of the corrosion resistance of these coatings. The total impedance values were measured as a function of time exposure in corrosive environment. We observed a continuous increase of the total impedance value with the time of exposure suggesting a possible self-healing effect due to the release of the inhibitors from the nanocontainers. Furthermore, addition of loaded nanocontainers into the coatings leads to the enhancement of the barrier properties of the coatings. Conclusively, we observed an improvement of the performance of the coatings due to the loaded nanocontainers.     

Protective behaviors of 2-mercaptobenzothiazole intercalated Zn–Al-layered double hydroxide coating

A nanocontainer with 2-mercaptobenzothiazole (MBT)-intercalated Zn–Al-layered double hydroxides (LDHs) was synthesized through co-precipitation. The structures of the LDH and the nanocontainer were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analysis. The nanocontainer was added into 3.5 wt% NaCl solutions with different pH values to study its effect on the protection of Q345 steel. The corrosion rate of Q345 steel in 3.5 wt% NaCl solution with a pH value of 3 was lower than those in neutral and alkali solutions. Moreover, the addition of nanocontainers into the epoxy resin coating improved the performance of the coating and facilitated self-healing by releasing MBT inhibitors into the scratched area.     

Hollow mesoporous silica nanoparticles loaded with phosphomolybdate as smart anticorrosive pigment

Recent developments in surface science and technology open up new opportunities for the development of smart pigments through the integration of nanoscale containers loaded with active components into coatings. Regarding the external factor to trigger the inhibitor release, a change in pH is a very interesting stimulus since corrosion activity leads to local changes in pH. Although several types of nanocontainers and encapsulation approaches have been proposed and studied to meet this goal, mesoporous silica nanoparticles (MSNs) are especially interesting as they retain their solid properties as long as pH of the surrounding medium does not exceed ~11. On the other hand, the use of hollow mesoporous silica nanoparticles (HMSNs) with a large cavity inside each original mesoporous silica nanoparticle has recently gained increasing interest due to the higher loading capacity. In the present work, an environmentally friendly corrosion inhibitor with good anticorrosive behavior when applied on steel substrates, sodium phosphomolybdate, has been successfully loaded and encapsulated on HMSNs. The pH-dependent release of the corrosion inhibitor from the loaded/encapsulated HMSNs has been confirmed. In addition, an improved anticorrosive behavior of the coatings formulated with loaded/encapsulated HMSNs has been observed by Scanning Kelvin Probe (SKP).     

Corrosion inhibition of steel using mesoporous silica nanocontainers incorporated in the polypyrrole

Mesoporous silica nanocontainer powders were applied as corrosion inhibitor hosts. These powders were dispersed in the polypyrrole matrix by electropolymerization technique. The protection properties of these composite coatings with and without inhibitor were studied in 2 g dm⁻³ chloride ion solutions at constant pH. Open circuit potential (OCP), inductive coupled plasma (ICP), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared spectroscopy (FTIR) results showed that the substrates were protected due to the release of corrosion inhibitor from mesoporous silica in the chloride media compared to the coatings without corrosion inhibitor. The released corrosion inhibitor reacted with substrate and made a protective phase during corrosion. This phase can heal the corroded area as a self-healing compound.     

Corrosion inhibition of magnesium using biocompatible Alkyd coatings incorporated by mesoporous silica nanocontainers

In the present study, mesoporous silica nanocontainer powders with and without inhibitor (fluoride) were dispersed in the Alkyd coatings to improve corrosion resistance of Mg metal. Then, the corrosion behavior of these coatings was studied in comparison with Mg in 2 g dm⁻³ NaCl solution. Electrochemical tests showed that these coatings could protect the surface from chloride attack. Moreover, release of fluoride from mesoporous silica nanocontainers leads to the formation of MgF₂ as an inhibitive compound at the interface.     

Smart self-healing anti-corrosion vanadia coating for magnesium alloys

Eco-friendly vanadia based chemical conversion coating was applied for improving the corrosion resistance of a newly developed magnesium AZ31 HP-O alloy. The effect of vanadia solution concentrations (10, 30 and 50 g/l) and pH (neutral pH 7 and pH 9) on the corrosion protection performance of a magnesium substrate were investigated. EIS and linear polarization techniques were used to evaluate the electrochemical behavior in 3.5% NaCl. The results showed a marked increase in the localized corrosion resistance after applying vanadia surface treatment of 50 g/l due to self-healing effect. The optimum conditions to obtain protective coatings for AZ31 HP-O with a self-healing ability were determined. Changes in surface morphology, composition and microstructure of the conversion coatings were followed by SEM-EDS and macroscopic imaging techniques.     

Self-healing waterborne polyurethane coating by pH-dependent triggered-release mechanism

In this study, effect of high-loaded silica capsules with corrosion inhibitor on thermal degradation and self-healing properties of waterborne polyurethane (WPU) was investigated. Silica capsules were synthesized using an oil in water (O/W) microemulsion and WPU was prepared via the prepolymer method. Assembled capsules demonstrated pH dependent release of their core. Incorporating silica capsule as an inorganic component resulted to improve thermal and barrier properties of WPU coatings. WPU coating with 1% silica capsules demonstrated better barrier quality in corrosive media and adding more than that resulted a rapid deterioration in barrier properties. Furthermore, such coatings possess an excellent adhesive strength with steel substrate. Electrochemical impedance spectroscopy was used in corrosion monitoring and healing procedure. Moreover, capsule morphology and thermal degradation of the WPU coating has been investigated separately by scanning electron microscopy and thermal gravimetric analysis. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47082.     

基于纳米容器BTA@MSNs-PAA的智能防腐涂层的制备及性能

碳钢被广泛应用于工农业生产中,智能涂层的研究和应用为碳钢的腐蚀防护提供了新的途径。本文以正硅酸乙酯（TEOS）为原料,通过加入扩孔剂1,3,5-三甲苯（TMB）合成了大孔径的介孔SiO₂纳米容器（MSNs）,采用聚丙烯酸（PAA）对MSNs进行化学修饰制备了一种装载缓蚀剂苯并三氮唑（BTA）的pH敏感性智能纳米容器BTA@MSNs-PAA。通过扫描电子显微镜（SEM）、动态光散射粒径分析（DLS）、X射线衍射分析（XRD）、傅里叶红外光谱（FTIR）、热重/差热分析（TGA/DTA）和紫外可见光谱（UV-vis）对BTA@MSNs-PAA的结构和性能进行了表征。通过将BTA@MSNs-PAA掺杂到环氧树脂涂层中,在碳钢表面制备了一种智能防腐涂层,采用电化学阻抗谱（EIS）和盐雾加速腐蚀试验对智能涂层的防腐性能进行了评价。结果表明,BTA@MSNs-PAA近似呈球形且表面光滑,平均粒径为320nm。BTA@MSNs-PAA可通过PAA与BTA之间的静电相互作用装载BTA分子,其装载量可达16.49%,BTA@MSNs-PAA可响应酸性刺激而加速释放BTA分子。基于BTA@MSNs-PAA的智能防腐涂层对碳钢表现出显著的腐蚀防护性能,这可能是因为当碳钢基体发生腐蚀时,其腐蚀点位下降的pH触发纳米容器快速释放BTA分子,从而有效抑制了基体的进一步腐蚀。     

Corrosion study of hybrid sol–gel coatings containing boehmite nanoparticles loaded with cerium nitrate corrosion inhibitor

To improve the corrosion protection of sol–gel derived hybrid silica/epoxy coatings containing boehmite nanoparticles, inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles. The morphology and chemical structure of the deposited films were studied by Scanning Electron Microscopy (SEM) and Fourier Transformed Infra-red Spectroscopy (FT-IR). The anticorrosion and self-healing properties of the coatings were evaluated by Electrochemical Impedance Spectroscopy (EIS). The high corrosion resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at the defects within the coating, hindering the corrosion reactions at defective sites.     

Corrosion study of hybrid sol–gel coatings containing boehmite nanoparticles loaded with cerium nitrate corrosion inhibitor

To improve the corrosion protection of sol–gel derived hybrid silica/epoxy coatings containing boehmite nanoparticles, inorganic corrosion inhibitor was introduced into the coating via encapsulation in the nanoparticles. The morphology and chemical structure of the deposited films were studied by Scanning Electron Microscopy (SEM) and Fourier Transformed Infra-red Spectroscopy (FT-IR). The anticorrosion and self-healing properties of the coatings were evaluated by Electrochemical Impedance Spectroscopy (EIS). The high corrosion resistance performance of such coatings is due to the presence of encapsulated cerium nitrate corrosion inhibitor that can be released at the defects within the coating, hindering the corrosion reactions at defective sites.     

Impact of inhibitor loaded mesoporous silica nanoparticles on waterborne coating performance in various corrosive environments

This article is a contribution to the development of the smart, self-healing solutions in the context of corrosion protection of metallic materials based on nanotechnology. Mesoporous silica nanoparticles were successfully synthesized and loaded with two different corrosion inhibitors, 1-hydroxybenzotriazole and 8-hydroxyquinoline. Loaded particles were embedded in different concentrations in waterborne epoxy coating, and as such applied to low carbon steel substrates. A continuous immersion test in 3.5% NaCl solution, humidity chamber exposure, and salt spray exposure were performed. Successful synthesis of silica nanoparticles has been demonstrated using scanning electron microscopy and energy-dispersive X-ray spectroscopy characterization techniques. Fourier transform infrared spectroscopy was used to confirm the loading of inhibitors, while the quantity of loaded inhibitors was determined by thermogravimetric method. Anticorrosive performance of intact composite coatings was determined using electrochemical impedance spectroscopy and open-circuit potential measurements. Adhesive properties were determined using the pull-off test (ISO 4624). Significant improvement in corrosion protection performance has been demonstrated for coatings containing inhibitor-loaded nanoparticles.     

A review on self-healing coatings based on micro/nanocapsules

Polymer coating systems are classically applied on a metal surface to provide a dense barrier against the corrosive species. Coatings are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Major advances for automatic repairing of defects have been made in the present decade within the field of self-healing polymeric materials. One of the most significant types of smart coatings is self-healing coating, which has the ability to release encapsulated active agents in a controlled way. They can be employed to develop a new family of smart multifunctional coatings. Incorporating micro/nanocapsules in coating matrix provides release of repairing agent rapidly after triggering due to crack propagation in coatings and gifts the self-healing to the coatings. This review covers the effective parameters in synthesis of micro/nanocapsules, several approaches to fabricate self-healing coatings based on these capsules and disadvantages of embedding them in coatings matrix. Current comprehensive review also provides all the knowledge of self-healing coatings based on micro/nanocapsules to whom that are concerned with coatings and corrosion prevention.     

自修复微胶囊及其防护涂层应用研究进展

随着自修复技术的不断发展,微胶囊在防护涂层等领域日益表现出突出的应用优势。文中综述了单壁、双壁自修复微胶囊的配方设计与结构性能以及微胶囊的模拟仿真研究现状,综述了以异氰酸酯、环氧树脂、缓蚀-腐蚀抑制剂、植物油为修复剂的自修复微胶囊在防护涂层中的应用研究进展,总结了现有微胶囊自修复材料存在的问题,提出了将自修复微胶囊与分子动力学模拟相结合的研究方法,希望通过该方法建立微胶囊宏微观结构与性能的关联性规律,实现对微胶囊自修复机理的深入探索与研究。     

Synergistic effect of silane modified nanocomposites for active corrosion protection

This work presents an effective anticorrosion behavior of a hydrophobic surface on stainless steel 304. The protective coating has been designed by dispersing nanocomposites (cloisite 15A, multiwalled carbon nanotubes and cerium chloride) which act as a corrosion inhibitor. The sol was prepared by using 3-glycidoxypropyltrimethoxysilane (GPTMS), octyltriethoxysilane (OTES) and zirconium (IV) butoxide as precursors. The corrosion resistance of coated stainless steel got improved when nanocomposites were homogeneously embedded in silica sol. The influence of nano-particles on the barrier coatings impedes corrosion. The coatings were analyzed by X-ray diffraction (XRD) to ensure the intercalation and distribution of nanocomposites in layered silicates. Fourier transform infrared spectroscopy (FTIR) was employed to characterize the nanocomposites modified silica sol. Scanning electron microscopy (SEM) was used to examine the morphology of the modified silane coating. The contact angle measurements ensured the hydrophobic behavior of the coatings. The corrosion behavior was investigated using Electrochemical Impedance Spectroscopy (EIS). This study has led to a better understanding of active anticorrosive coatings with embedded nanocomposites and the factors influencing the anticorrosion performance.     

Lithium salts as leachable corrosion inhibitors and potential replacement for hexavalent chromium in organic coatings for the protection of aluminum alloys

Lithium salts are being investigated as leachable corrosion inhibitor and potential replacement for hexavalent chromium in organic coatings. Model coatings loaded with lithium carbonate or lithium oxalate demonstrated active corrosion inhibition and the formation of a protective layer in a damaged area during neutral salt spray exposure. The present paper provides an abridged overview of the initial studies into this novel inhibitor technology for the active corrosion protection of aluminum alloys. Coating defects were investigated by microscopic techniques before and after exposure to corrosive conditions. Scanning electron microscopy analysis of cross-sections of the coating defect area demonstrated that the protective layer comprises a typical three-layered structure, which included a dense layer near the alloy surface, a porous middle layer, and a flake-shaped out layer. Potentiodynamic polarization measurements obtained with a microcapillary cell positioned in the coating defect area and electrochemical impedance spectroscopy confirmed the corrosion protective properties of these protective layers. The long-term corrosion inhibition of the lithium-based coating technology was tested in industrial coating systems.     

Self-healing of TiSiN/Ag coatings induced by Ag

Ceramic coatings often suffer from the formation and expansion of microcracks, which leads to a failure of the protective function. In this work, we observed self-healing of the microcracks in the TiSiN/Ag multilayer coating upon heating. This behavior can be attributed to diffusion of the Ag atoms to the cracks in the multilayer coating, while similar cracks in the TiSiN monolayer coating remain unchanged after the same treatment. Furthermore, the TiSiN/Ag coating with healed cracks possesses similar electrochemical corrosion and biofouling properties to the as-deposited one, suggesting that TiSiN/Ag is a promising system in marine engineering applications. The mechanism of self-healing was explained by kinetic simulations based on ab initio molecular dynamics and the diffusion activation energies of Ag in irregular ceramic structures have been calculated. The here adopted theoretical method also provides a new pathway for exploring new coating systems with a potential self-healing function.