Organic Coatings Research Articles

Fabrication and mechanism study of the nitrocellulose aqueous dispersions by solvent displacement method

AbstractThe traditional preparation methods of nitrocellulose emulsion have many problems, such as high emulsifier content, complex preparation processes, or the need for high energy‐consuming emulsification equipment. To address these issues, in this paper, the emulsifier‐free NC dispersion was successfully prepared by a simple, low‐energy solvent displacement method for the first time and the formation and stabilization mechanism of NC nanoparticles was also thoroughly investigated. The formation mechanism of the NC particles based on the “nucleation and aggregation” and the stabilization mechanism of the NC aqueous dispersions based on the electrostatic repulsion of anions were proposed and supported by experimental results. At the same time, we achieved effective control of the solid content of the NC dispersion by vacuum concentration. The obtained NC dispersion had a large range of adjustable sizes (63.82–143.43 nm), uniform size distribution (PDI < 0.2), a wide range of tunable solid content (0.5%–16%), and good stability (zeta potential < −20 mV), which has potential application in adhesives and coatings as promising candidates for traditional NC organic coatings.

Synthesis and Characterization of Schiff Base Polymers via Metal Coordination and Its Application in Infrared Stealth Coating.

In order to reduce the infrared emissivity to meet the requirements of modern warfare for infrared stealth materials, we prepared the polymers containing Schiff base moieties using polyetheramine and 2,6-pyridinedicarboxaldehyde by solution polycondensation and coordinated with Ni2+, Cu2+, and Sm3+ ions to prepare organic coatings. The structure and the thermal and mechanical properties of the coatings were studied in detail. Meanwhile, the effect of the conductivity change of coordination polymers on infrared emissivity was studied systematically. The results showed the polymer coordinated with Sm3+ ions had the lowest energy band gap, which was 2.99 eV, and the best electrical conductivity of 3.54 × 10-4 S/cm compared with Ni2+ and Cu2+ coordination polymers. The infrared emissivity was the lowest in the 2-22 μm infrared waveband range, which reached 0.58, suggesting the polymers containing Schiff base moieties and their coordination polymers may have a great potential to be applied as infrared stealth materials in military applications.

Infrared Reflection-Absorption Spectroscopy of α-Hydroxyacids at the Water-Air Interface.

Organic molecules, including α-hydroxyacids, are ubiquitous in the natural environment. Often found at water-air interfaces, organic molecules can alter the structure of the interface or participate in interfacial chemistry. Despite their prevalence in the environment, the structure and ordering of α-hydroxyacids have not been widely investigated at water-air interfaces, and the impact of the hydrophobic tail length on structure has not been explored. Here, for the first time, we use infrared reflection-absorption spectroscopy to assess the vibrational structure of α-hydroxyacids at a water surface as a function of surface partitioning and surface coverage. We study lactic acid, 2-hydroxyoctanoic acid, and 2-hydroxystearic acid, which have 1 carbon, 6 carbon, and 16 carbon tails, respectively. Vibrational features compared across the set of α-hydroxyacids studied here are used to determine the interaction of the polar headgroup with the water subphase and the ordering of the hydrophobic tail. We find that the carbonyl and α-hydroxyl groups participate in a complex hydrogen-bonding motif at the water-air interface that can be affected by the hydrophobic tail length and places the polar headgroup in or below the water-air interface. Furthermore, molecular ordering increases with the tail length or the surface coverage. The presence of the α-hydroxyl group causes the α-hydroxyacids to maintain a tilted orientation with respect to the surface normal even at high surface coverages. A combination of polar headgroup and hydrophobic tail effects dictates the overall orientation of α-hydroxyacids and can thus affect their ability to participate in chemistry and alter organic coatings on water surfaces.

Inhibition mechanism of anticorrosion pigments leached from organic coatings: Comparison between salt spray and immersion testing

In this work, cerium 4-hydroxycinnamate (Ce(4OHCin)3) and strontium zinc phosphosilicate (SZP 391) were separately incorporated as leachable anticorrosive pigments in model organic coatings for safeguarding the structural integrity of AA2198-T851 aluminium alloy under neutral salt spray (ASTM B-117) and immersion test conditions. The coated samples were artificially damaged with a scribe to reveal the underlying substrate. After 840 h of salt spray and immersion tests, the unexposed and exposed samples were characterized with scanning electron microscopy (SEM), interferometry, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). The SEM and interferometry revealed relatively rough surface morphology and porous networks due to the dissolution and release of large inhibitor clusters from the organic coatings. These networks provide pathways for transport of inhibitive species. The leached inhibitive species formed a precipitate of protective film in the scribed surfaces, whereas the XPS detected and provided information about the oxidation state of the protective species. EIS study has confirmed the inhibitive properties of the adsorbed film by significantly increasing the impedance modulus of the substrate. The protective films revealed a monolayer structure.

Thermo-chemo-mechanical influences of impingement flow on the degradation of organic coatings in the underwater zone of offshore wind turbines

Thermo-chemo-mechanical influences of impingement flow on the degradation of organic coatings in the underwater zone of offshore wind turbines

The Boundary Between Volume and Surface-Driven Magnetic Properties in Spinel Iron Oxide Nanoparticles

Despite modern preparation techniques offer the opportunity to tailor the composition, size, and shape of magnetic nanoparticles, understanding and hence controlling the magnetic properties of such entities remains a challenging task, due to the complex interplay between the volume-related properties and the phenomena occurring at the particle’s surface. The present work investigates spinel iron oxide nanoparticles as a model system to quantitatively analyze the crossover between the bulk and the surface-dominated magnetic regimes. The magnetic properties of ensembles of nanoparticles with an average size in the range of 5–13 nm are compared. The role of surface anisotropy and the effect of oleic acid, one of the most common and versatile organic coatings, are discussed. The structural and morphological properties are investigated by X-ray diffraction and transmission electron microscopy. The size dependence of the surface contribution to the effective particle anisotropy and the magnetic structure are analyzed by magnetization measurements and in-field Mössbauer spectrometry. The structural data combined with magnetometry and Mössbauer spectrometry analysis are used to shed light on this complex scenario revealing a crossover between volume and surface-driven properties in the range of 5–7 nm.Graphical

Development of a Framework for Modeling Protection Mechanisms Provided By Multi-Layered Organic Coatings Applied to Aerospace Al Alloys Via Finite Element Analysis

Aluminum alloys, such as AA2024 and AA7050, are widely used in aerospace applications due to their high strength-to-weight ratio. However, because of the heterogeneous microstructure of these alloys, they are susceptible to microgalvanic corrosion and pitting in chloride-containing environments. The corrosion susceptibility is further increased when these alloys are in contact with more noble alloys, such as in locations near fasteners, where the galvanic interaction leads to accelerated corrosion attack of the less noble Al alloy. To protect these structures against corrosion attack, organic coatings are commonly used. Typical coating systems are usually composed of three layers: a conversion coating, a primer, and a topcoat. When the topcoat is breached, the primer can provide active corrosion protection by the release of inhibitors embedded in the primer. Depending on the type of inhibitor, it can provide chemical protection by the formation of a passive film on the surface of the exposed metallic area and/or provide cathodic protection by the preferential dissolution of sacrificial anodes.The efficacy of the corrosion protection provided by the multilayered coating system to Al alloys in aircraft components exposed to atmospheric corrosion is affected by a large number of variables. The dynamic environment in which the component is exposed to (e.g., relative humidity, temperature, salt loading density), the geometry of the component, the chemistry of the primer, and the type of alloy are examples of important parameters that impact the corrosion and protection mechanisms. To unravel the impact of each one of these variables and/or the synergistic effects between them, a large volume of experimental work is needed, making the prediction of coating failure, corrosion damage, and, ultimately, component lifetime, remarkably challenging. In this context, the development of computational models that can simulate corrosion and corrosion protection mechanisms is attractive, as they can be used as tool to effectively assess the large parameter space and increase efficiency of experimental work.This work focuses on developing a framework for modeling the protection mechanisms offered by chromate-based and Mg-rich primers via finite element analysis. Chemical and electrochemical protection mechanisms were modeled taking into consideration leaching of inhibitor from the primer, mass transport and the impact of the inhibitors in the electrochemistry of the Al alloys. The impact of environmental, geometric, and coating parameters on the effectiveness of the protection mechanisms was assessed. Ultimately, the framework developed will provide a better understanding of protection mechanisms of the organic coating systems and serve as a framework to study new coating systems.

Electrochemical Assessment of Galvanized Steel Corrosion in Alkaline Sulfate Solution

Corrosion of steel prestressing strand in bonded post-tensioned bridge tendons have been associated with elevated concentrations of sulfate ions in deficient grout that can develop due to grout segregation [1]. Previous research indicated that the early presence of elevated sulfate ion concentration in the deficient grout in contact with the embedded steel can impair steel passivity. Metastable pitting was observed for steel in saturated calcium hydroxide solutions with sulfate ion concentrations greater than 1,300 ppm and pitting was observed in solutions above 20,000 ppm [2-4]. In addition to steel strand corrosion, galvanized steel ducts in direct contact with the deficient grout with elevated sulfate ion concentrations were also observed to have severe localized corrosion [1]. Galvanized steel in alkaline solutions, such as in cement pore water, have been characterized to have greater resistance to chloride-induced corrosion with chloride threshold concentrations as much as 2.5 times greater than carbon steel [5]. Information relating to sulfate concentrations is less available. Electrochemical testing including the electrochemical noise (EN) technique was conducted to identify the role of early sulfate ion presence on corrosion of galvanized steel.EN provides a test method to assess the corrosion modality without the influence of an external excitation that can affect the electrode surface and electrolyte chemistry (such as metal oxidation and oxygen reduction) [6-7]. The testing aims to identify the corrosion mitigation characteristics of the galvanized steel such as zinc activity and protective barrier surface oxide layers in presence of sulfate ions as well as combined cases with chloride ion contamination below reported threshold concentrations for galvanized steel. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential, linear polarization test, and electrochemical impedance spectroscopy). References K. Lau, and I. Lasa. "Corrosion of prestress and post-tension reinforced-concrete bridges." Corrosion of steel in concrete structures. Woodhead Publishing, 2016. 37-57. DOI: https://doi.org/10.1016/B978-1-78242-381-2.00003-1.S. Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Initiation of localized steel corrosion in alkaline sulfate solution.” Materials and Structures, 54 (2021), pp.1-17.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Identification of steel corrosion in alkaline sulfate solution by electrochemical noise.” Materials and Corrosion, 72(2021), pp.1456-1467.S. Yeomans. Galvanized steel reinforcement in concrete. Elsevier, 2004.S. Permeh, and K. Lau. "Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations." ECS Meeting s. No. 10. IOP Publishing, 2021.K. Lau, S. Permeh. “Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique.” Progress in Organic Coatings, 167(2022): 106840.

Predicting Atmospheric Corrosion of Aluminum 2024 Coupons in Coastal Environments with Data Analytics

How can we design short-term laboratory corrosion tests to adequately simulate long-term outdoor atmospheric corrosion? To achieve this objective, models need to be devised to rank and quantify critical environmental variables that influence atmospheric corrosion. This effort provides a data-driven analysis of environmental factors that can be used to quantitatively model atmospheric corrosion aluminum alloy 2024-T3 (AA2024-T3) samples placed at three unique coastal sites in the state of Florida, USA, for various time periods over an 18-month total period of exposure.Atmospheric corrosion proceeds via several processes that take place in sequence and/or in parallel across multiple classes of matter: the atmosphere, condensed aqueous solution, organic coatings, oxide scales, precipitated salts, and microstructurally heterogeneous metal alloys. Several physical and chemical phenomena contribute to the process of corrosion, including mass-transport, electrochemical effects, metal dissolution, grain-boundary transport, etc. For this reason it is difficult to directly predict, using fundamental physics or chemical principles, the corrosion rate of a metal in its environment. Likewise, it is difficult to directly extrapolate the results of short-term tests to long-term tests solely from physical principles. A modeling approach that pairs data analytics with scientific insight is required.To support this objective, data was collected for AA2024-T3 coupons based on exposure over an 18-month period at three coastal sites in Florida, USA. Methods to summarize the environmental exposure metrics for each time period were developed using standard statistical metrics (mean, standard deviation) as well as a more complete set of metrics, known as the Catch-22 algorithms, developed by The University of Oxford.The corrosion coupon data was aggregated into a data framework that included the metrics of mass loss per unit area, linear corrosion rate, and a parabolic corrosion constant, as well as generation of additional data by sample differencing that considers cumulative corrosion occurring between time periods.An automated approach was then developed that queries public and/or pay-to-access websites for environmental data to build an exposure profile for a sample placed at a known location (specified by latitude/longitude) and over a given range of dates. We evaluated 288 total variables in the exposure profile. Of these 288 variables, five key variables were determined to have a quantitative effect on the corrosion rate and mass loss per unit area, and these include mean precipitation, the range of temperatures, the minimum wind speed, the standard deviation of ozone exposure, and the maximum solar irradiance.This work serves to help with the selection of appropriate variables to be used in designs for a laboratory-simulation exposure chamber that would mimic service environment and accelerate the development of advanced materials degradation test protocols. The approach developed herein can be applied to other materials of interest, different locations, and adapted to other metrics of corrosion such as localized corrosion depth and volume, due to pitting.

Anti-Corrosive and Anti-Bacterial Polymeric Coatings Consisting of PCL and Lawsone

The clinical application of magnesium (Mg)-based alloys as biodegradable orthopedic implants is highly restricted because of their rapid corrosion rate in the physiological environment [1]. Polymeric coatings have been recognized as one of the most effective methods to tailor the corrosion rate of Mg alloys without changing their bulk properties, while providing them with other functionalities such as enhanced biocompatibility and antibacterial properties [2]. In this study, a bi-layered anti-corrosive polymeric coating based on polycaprolactone (PCL) and lawsone, a natural corrosion inhibitor extracted from the leaves of Lawsonia inermis plant, was fabricated on AZ31 Mg alloy to improve its corrosion resistance. The result of electrochemical and in vitro immersion studies clearly demonstrated the corrosion inhibitory effect of lawsone and the enhanced corrosion resistance of AZ31 alloy by almost two orders of magnitude (inhibition efficiency of 98.3%) after being coated with PCL-lawsone. Moreover, coated AZ31 substrates exhibited significantly hampered local alkalization and excessive H2 generation. Apart from the corrosion inhibition properties, incorporation of lawsone imparted a strong antibacterial activity to the coating, which is helpful in the prevention of microbial infection and early implant failure. While most of the commonly used corrosion inhibitors are known to be toxic and have limited biomedical applications, no cytotoxic effect was observed for lawsone-containing coating toward human fetal osteoblast cells (viability of > 85%). The findings of this work highlighted the great potential of lawsone as a natural corrosion inhibitor for fabrication of corrosion protective, antibacterial, and biocompatible coatings on Mg-based biodegradable implants. References Wang, Jia‐Li, et al. "Biodegradable magnesium‐based implants in orthopedics—a general review and perspectives." Advanced science 7.8 (2020): 1902443. Asadi, Hamid, et al. "A multifunctional polymeric coating incorporating lawsone with corrosion resistance and antibacterial activity for biomedical Mg alloys." Progress in Organic Coatings 153 (2021): 106157.

Kelvin Probe Techniques in Corrosion Science: An Overview of the Latest Developments

Over the last years, Kelvin probe techniques have found a more and more widespread application in corrosion science. While the pioneering applications by Stratmann et al were focused on investigating corrosion underneath ultra-thin electrolyte layers to cathodic delamination of organic coatings [1, 2], over the last 15 years the Kelvin probe method was shown to be applicable for new applications such as mapping hydrogen activities, measuring hydrogen permeation [3] and even measuring oxygen reduction at buried interfaces [4] or on surfaces just covered by a monolayer of water [5].In this contribution examples about the latest developments of its application in corrosion science will be presented, from coating delamination to hydrogen in materials.[1] M. Stratmann, H. Streckel, Corros. Sci., 30 (1990), pp. 681-696[2] M. Stratmann, H. Streckel, R. Feser, Corros. Sci., 32 (1991), pp. 467-470[3] S. Evers, M. Rohwerder, Electrochemistry Communications 24 (2012) 85[4] D. Vijayshankar, T.H. Tran, A. Bashir, S. Evers. M. Rohwerder, Electrochimica Acta 189 (2016) 111-117[5] X.K. Zhong, M. Schulz, C.H. Wu, M. Rabe, A. Erbe, M. Rohwerder, Chemelectrochem 8(4) (2021) 712-718

Effect of immersion time and pH variation on the inhibition of AA2198-T851 alloy by leaching of anticorrosion pigments from free-standing films of organic coatings

In this work, organic coating films loaded with leachable anticorrosive pigments, cerium 4-hydroxycinnamate (Ce(4OHCin)3) and strontium zinc phosphosilicate (SZP 391) were immersed in 3.5% NaCl solution at pH 3, pH 5.6, and pH 10. Extracts from each bulk solutions were taken after 24 h, 72 h, 168 h, 240 h, and 336 h to quantitatively measure the leaching of the inhibitive species as a function of time using inductively coupled plasma optical emission spectroscopy (ICP-OES). Other part of the extracts was also employed as test solution to monitor the inhibitive properties of the leached species on AA2198-T851 substrates using electrochemical impedance spectroscopy (EIS). After the immersion process, the unexposed and exposed film surfaces were characterized using optical microscopy, transmission, and scanning electron microscopy (TEM & SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The leaching test results confirmed the release of inhibitive species from the coating films into the test solutions, whose rate increased with immersion time but decrease with increasing pH of the bulk solution. Greater leaching rate was observed at the lowest pH, whose release follows non-Fickian diffusion. Furthermore, the EIS results indicated significant protection of the alloy and the efficiency increased with increasing immersion time and decreasing pH. The extract with Ce(4OHCin)3 pigment shows comparatively higher release rate and better inhibitive properties, with the best at the lowest pH 3. This is attributed to its smaller cluster size and high solubility. The optical and electron Microscopy, XRD and FT-IR of coating films have further complemented the leaching process by revealing pores left behind due to dissolution of large clusters. The pores networks provided excellent transport path for both inward migration of aggressive solution and the release of dissolved inhibitive species.

Thermal Stability of Organic Coatings for Aluminium and Its Environmental Aspects

Thermal stability of organic coatings for aluminum plays a key role not only in specific applications, but also in the recycling process of aluminum scrap. For production of secondary aluminum it is necessary to remove coatings from scrap. Rests of unremoved coatings affect the quality of final aluminum. Most of methods for coatings removing are based on thermal decomposition. This process leads to emission of various organic compounds which present potential risk for human health and also for environment. Thermal stability of all tested coatings with in-creasing temperature was study with use of thermogravimetric analysis (TGA). Significant degradation of coating started at temperature 200 °C and at temperature 450 °C was most of the tested coating degraded and remained only inorganic part of coating. Inorganic part render ap-prox. 30 % of the original coating mass. Degradation of tested coatings was also confirmed by Fourier transform infrared spectroscopy (FTIR) analysis. This work also deals with study of in-organic/organic ratio of hybrid coating on real sample of scrap for recycling. The thermolabile part of coating is degraded during heating, which lead to emission of organic compounds and products of degradation which can affect human health and also the environment.

Coupled effect of water absorption and ion transport in hydrated latex anti-corrosion coatings

Water-based anti-corrosion coatings, which are environmentally-friendly replacements for organic solvent-based coatings, do not perform well enough for use in the most challenging corrosion environments. The high water absorption capacity of water-based latex films may reduce barrier performance by contributing to corrosive reactant/product transport. We seek to understand the coupled effects of water absorption and ion transport in hydrated latex films, and to propose mechanisms explaining these effects. Water absorption and ion transport in films immersed in deionized (DI) water were monitored by mass gain and electrical conductivity measurements, respectively. Despite very similar polymer compositions between films, large differences in water absorption and ion transport rates were observed and explained by percolating networks at latex particle boundaries which facilitate transport. A semi-continuum model with three-component diffusion and convection-like elastic relaxation supported the assumptions of the physical mechanisms governing water absorption and ion transport. The evidence of the coupled processes of water absorption and ion transport in hydrated latex films revealed in this study are useful for designing water-based coatings that provide high levels of corrosion resistance.

Corrosion Properties and Bond Strength of Coated (PE/PAK; Pe/PPE; PAD) Reinforcement (B500B) with Normal Strength Concrete

The paper verifies anti-corrosion barrier protective properties of PE/PAK (polyethylene/polyacrylate), PE/PPE (polyethylene/polyproplylene) and PAD (polyamide) coatings of specific thickness on the surface of conventional ribbed bar B500B. Using pull-out test, the bond strength of such system was compared with bond strength of normal strength concrete (C30/37). Results of these tests show that key properties of coated systems are comparable to the previously tested epoxy coatings in case of their use in technical practice (protection of conventional rebar). In conclusion, their effective protective effect corresponds to minimal thickness higher than 300 μm but simultaneously lower the bond strength between the ribbed rebar and concrete. Keywords: corrosion of steel in concrete, organic coatings, bond strength, pull-out test, porosity

The design and preparation of high-performance ABS-based dielectric composites via introducing core-shell polar polymers@BaTiO3 nanoparticles

In consideration of inherent high hysteretic losses resulting in low energy efficiency for ferroelectric polymer, linear dielectric acrylonitrile butadiene styrene (ABS) with low price and good film property is adopted as optimal polymer matrix. Synchronously, representative ferroelectric barium titanate (BT) nanoparticles with high dielectric constant are selected as the nanofiller. To weaken the surface energy of BT nanoparticles and boost the interfacial interaction, polar polymer (poly[bis(4-cyanophenyl) 2-vinylterephthalate] (PBCN)) is employed as organic coatings to regulate interfacial property. Consequently, core–shell structured PBCN@BT nanoparticles were synthesized by means of reversible addition-fragmentation chain transfer polymerization combined with thiol-ene click reaction and the corresponding ABS-based nanocomposites were prepared. In consequence, discharge energy density increased from 3.2 J/cm3 for the pure ABS film to 4.5 J/cm3 for the 0.5 vol%-PBCN@BT/ABS nanocomposites. Meantime, a high energy efficiency of 76% was found. This discovery is of great significance for the development of excellent performance ABS-based dielectric composites.

Distribution parameters of a plastic–elastic transition function for normal force effects on the abrasive wear of organic coatings

Distribution parameters of a plastic–elastic transition function for normal force effects on the abrasive wear of organic coatings

Corrosion failure process of organic conductive coating on Mg-RE alloy with PEO in the simulated Xisha atmospheric solution

Organic conductive coating/plasma electrolytic oxidation (PEO) coating/Mg-RE alloy is a simple way to meet the functional requirements and service safety of electronic equipment. In this work, the Macro electrochemistry, micro electrochemistry and mechanical test were performed to study the corrosion failure process of organic conductive coatings and PEO coating on the surface of Mg-RE alloy under the harsh marine atmospheric environment. Organic conductive coatings have protective effect on Mg-RE with PEO coating (the impedance modulus remain higher than 106 at low frequencies during 21d immersion, and the characteristics of EIS remained constant). But local failure of bonding between organic conductive coating and PEO coating were occurred after being immersed in Xisha simulation solution and it weakened the long-term protection ability of organic conductive coating/PEO coating/Mg-RE alloy system, which limited long-term corrosion resistance.

Effect mechanism of the Fe3O4 nanoparticles on mechanical properties and anticorrosion performances of epoxy coatings

The hydrophobic magnetic Fe3O4 nanoparticles (OMNPs), which were synthesized via the co-precipitation method and following modification with oleic acid, appeared excellent hydrophobic and lipophilic properties after being characterized both in water and in epoxy resin. Furthermore, the mechanical and anticorrosion properties of the OMNPS modified epoxy coatings were characterized by tensile stress test, indentation hardness test, adhesion strength test, and Electrochemical Impedance Spectroscopy (EIS) technique. The results showed that both mechanical properties and the corrosion resistance of the epoxy coating could be significantly affected by the surface modification and the addition amount of OMNPs, which provided a possible approach to enhance the anticorrosion ability of epoxy organic coatings.

A double-layered self-healing coating system based on the synergistic strategy of cysteine and iron polyacrylate for corrosion protection

Nanocontainers loaded with corrosion inhibitors are usually added to organic coatings to achieve self-healing of the coating. However, the amount of nanocontainers that the coating can accommodate is limited. Excessive addition of nanocontainers will damage the integrity of the coating, while too little addition will lead to its insufficient self-healing ability. Here, we prepared a double-layered self-healing coating system (C-DMS-EP/P-DMS-EP) consisting of a bottom epoxy coating containing cysteine (CysH) loaded dendritic mesoporous silica (DMS) (C-DMS-EP) and an upper epoxy coating containing iron polyacrylate (PAAFe) loaded DMS (P-DMS-EP) based on the synergistic effect of CysH and PAAFe. It can achieve more efficient self-healing ability for Q235 steel. The experimental results exhibit that PAAFe can not only accelerate the oxidation of CysH but also capture the hydrogen ions generated during the oxidation process, thereby exhibiting excellent corrosion resistance. Electrochemical impedance spectroscopy (EIS) results show that the low frequency impedance modulus (|Z|0.01 Hz) of C-DMS-EP/P-DMS-EP is nearly-two orders of magnitude higher than that of pure epoxy coating (EP) after 40 days of immersion in 3.5 wt% NaCl solution. Moreover, the self-healing efficiency (ηs) of C-DMS-EP/P-DMS-EP with an artificial scratch (C-DMS-EP/P-DMS-EP@AS) gradually changes from negative to positive as the immersion time increases. The preparation method for this double-layered self-healing coating system proposed in this work will provide a new idea for constructing high-performance self-healing coatings.