Smart Coatings Research Articles

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

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

Fabrication of an intelligent anti-corrosion silane film using a MoO42− loaded Micro/mesoporous ZIF67-MOF/multi-walled-CNT/APTES core-shell nano-container

The design of smart coatings for corrosion protection aims has become one of the most interesting hotspots for contemporary corrosion researchers. For this purpose, scientists mostly grabbed on the utilization of carriers with control-release capability, and carbonaceous materials are the most well-known celebrities among all. In this work, the multi-walled carbon nanotube (CNT) surface was decorated with ZIF67 crystals, and then MoO42− ions (Mo) were loaded into the constructed nano-carrier. Eventually, the synthesized particles' were covered by (3-Aminopropyl) triethoxysilane (APTES) amino silane for better dispersion in the silane matrix. The silanized and un-modified nano-hybrids were precisely explored by different characteristic methods to prove their successful synthesis. Also, the inductively coupled plasma (ICP) measurements demonstrated around 49 ppm, 18 ppm, and 0.02 ppm Co ions in the acidic, neutral, and alkaline conditions, respectively. The Electrochemical Impedance Spectroscopy (EIS) and polarization records in the solution phase revealed that CNT-ZIF67-Mo nano-hybrids successfully declined the corrosion rate of metal up to 91% and 84%, respectively. Thereupon, to design a self-healable anti-corrosion system, CNT-ZIF67-Mo particles at 0.15 wt% were incorporated into the silane-based hybrid coating. The EIS explorations carried out on the scratched composites proved that the total resistance was tripled and self-healing activity with a 69% index was visualized after the inclusion of APTES/CNT-ZIF67-Mo nanoparticles. Also, the EIS investigations over the intact composites declared that the silane coating resistance was increased from 23156 Ω.cm2 to 200169 Ω.cm2 and water uptake was around 73% upon the incorporation of APTES/CNT-ZIF67-Mo nanoparticles.

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

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

Zinc oxide nanoparticles as photo-catalytic and anti-bacterial pigment for alkyd resin based coating

Recently, there has been an upsurge among people around the world in maintaining a sustainable and hygienic environment. This is due to the over-exploitation of recourses causing environmental pollution and spreading bacterial infections. In this regard, scientists are motivated to develop smart coatings where environmental pollutants and bacterial cells are degraded when in contact with their surfaces.In our previous report, ZnO nanoparticles (NPs) were prepared using the precipitation technique, showing good photocatalytic and antibacterial activity [1]. In this context, the present study details the use of ZnO NPs as pigment for the fabrication of alkyd resin-based self-cleaning coating. The coating was developed by mixing ZnO NPs and alkyd resin along with the additives using the ball milling technique. The developed coating was characterized using field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, and water contact angle measurements.To elucidate the self-cleaning and hygienic behaviour of the ZnO/alkyd resin coating, the dried coating was exposed to crystal violet (CV) solution as a model dye pollutant and bacterial strains to assess its photocatalytic and antibacterial activity. The droplets of CV solution placed over the coating almost degraded after 360 min of exposure to sunlight owing to the presence of ZnO NPs in the coating. Further, the coating exhibits reasonable antibacterial activity against E. coli and P. aeruginosa whereas it displays low antibacterial activity against S. aureus.Even though, the self-cleaning coating shows promising results, tuning the activity of the photo-catalytic pigment can improve the pollutant degradation efficiency and elevate bactericidal activity.ZnO NPs-impregnated alkyd resin coating for self-cleaning applications is novel.

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

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

Modeling surface segregation of smart PU coatings at hydrophilic and hydrophobic interfaces via coarse-grained molecular dynamics and mesoscopic simulations

Developing adaptive coatings having desired functionalities at targeted interfaces is one of the major efforts in the coatings science area. The adaptation of the surface functionality to the changing surface conditions can be maintained by introducing dangling chains with different properties to the cross-linked polymer coatings. In this work, we strive to investigate the change in interfacial morphology of PU coatings as exposed to hydrophilic (HPI) and hydrophobic (HPB) interfaces by employing molecular simulations at the coarse-grained and mesoscopic levels. The molecular structure and surface segregation dynamics are studied for PU coatings having pure HPI, mixture of HPI and HPB, and amphiphilic dangling chains. The dual-scale simulations, Dissipative Particle Dynamics (DPD) and MARTINI model, yield results about the dangling chain structures at the interface in terms of their end-to-end distances, where HPI chains adopt a more extended conformation in water in comparison to oil interfaces. The reverse is observed to be valid for the HPB chains. Regarding the dangling chain dynamics, a swift migration towards the interfaces is noticed at about 10 ns for both of the simulation methods. The structures of the dangling chains and their interaction with the interfaces are also characterized by computing the radial distribution function (RDF) profiles. Preferential interactions between the HPI/water and HPB/oil are clearly noted. The switchability of the surfaces is also studied by simulating the system in cycles, such that the interface is changed from water to oil and back to water. The migration of HPI groups in the dangling chains towards water and vice versa in each cycle is clearly shown by the simulations. In all, the inherent structure and dynamics of the dangling chains is obtained at the molecular level by the dual-scale molecular simulations. Our findings reveal a significant level of understanding about interfacial morphology of thermoset coatings modified by dangling chains, where the results can be extended to find applications in guiding the experimental studies.

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

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

Nanoporous Metal-Organic Framework Thin Films with Embedded Fulgide for Light-Modulated Guest Adsorption and Diffusion.

Smart and photoresponsive materials and thin films allow the dynamic remote control of their central properties. By incorporation of photochromic molecules in nanoporous metal-organic frameworks (MOFs), the interaction between the MOF host and the guest molecules in the pores can be modified. Here, a MOF film of type UiO-68 is presented in which the photoswitchable feature is added by embedment of photochromic fulgide molecules of type Aberchrome 670 in the pores. The photoisomerization in the pores is explored by UV-vis and infrared spectroscopy, and the transient uptake of toluene and methanol probe molecules is explored using a quartz crystal microbalance. For the first time, a fulgide-based nanoporous material is used to remote-control the adsorption and diffusion properties. We find that the toluene uptake amount can be increased by 37% and the toluene diffusion coefficient can be increased by 40% when reversibly photoswitching the embedded fulgide from its E-form to C-form. In this way, this study aims to contribute to the field of light-responsive nanoporous materials and thus expands the range of smart coatings.

Visible light-triggered smart photoreversible color switching systems based on VOx QDs for constructing smart corrosion resistant coatings on AA2024-T3

Nanoparticles rich in oxygen vacancies (such as ZnO1-x, SnO2-x, TiO2-x, CeO2-x) are major components of Photoreversible color-switching systems (PCSSs) and are utilized in many applications (ink-free paper printing, secure communication and smart fabrics). Despite this, it has been a challenge to develop smart coatings due to several factors (such as low durability and poor efficiency in charge separation). To solve these issues, we have synthesized oxygen deficient vanadium oxide (VOx) quantum dots with a size of ∼ 2 nm through solvothermal reaction by using l-ascorbic acid as a reducing agent, resulting in widened photoabsorption spectrum with a band gap of 2.15 eV. Oxygen deficient VOx, methylene blue and acrylic latex (VOx/MB/Ac2403) have been used to design PCSSs coating on AA2024-T3 metal alloy. The redox dyes can be photocatalytically reduced by visible laser light, resulting in remote printing of various designs on the smart coating in ∼ 120 s. When irradiated with blue light, the designs can be erased in ∼ 250 s caused by the VOx self-catalyzed oxidation, leading to high recyclability (more than 40 cycles), efficiency and durability. As a result, reprintable smart coatings offer a viable alternative to regular alloys in meeting the growing demands for security or camouflage.

Graphene-based anti-corrosive coating on steel for reinforced concrete infrastructure applications: Challenges and potential

• State-of-the-art review of graphene coatings for infrastructure applications. • Critical comparison of monolithic, laminate, and nanocomposite graphene coatings. • Consideration of practical factors stability, scalability, cost, sustainability. • Nanocomposites have the strongest long-term anti-corrosion. • Graphene-based coating is promising for future research in steel rebar coating field. Steel corrosion has been a major perpetual issue of concern for durability and structural integrity of steel and reinforced concrete infrastructure. Polymeric, zinc-galvanic and chromate conversion coatings are commonly applied to protect typical steel materials such as structural steel, reinforcing steel bar (rebar), mild steel and light gauge steel used in infrastructure. Yet, due to physical integrity, long-term performance and environmental concerns, their applications have been limited. In recent years, graphene has garnered considerable attention in the field of anti-corrosive coatings and substantial progress has been achieved in the development of particular graphene-based monolithic (single/few-layer graphene and graphene oxides) as well as laminate and nanocomposite coatings. Despite considerable efforts dedicated towards fundamental research, the laboratory to industry transition of graphene-based anti-corrosive coatings remains challenging. To this end, this report reviews the state-of-the-art on graphene-based coating technology with application to steel surfaces and discusses, both, experimental studies and theoretical aspects. Specifically, this review presents (i) production of different forms of graphene-based materials and the coating process; (ii) corrosion resistance and anti-corrosive coating performance of graphene-coated steel materials, (iii) key potential areas and challenges pertaining to the application of graphene-based coating to structural steel and rebar; and (iv) potential future directions towards corrosion protection and smart coatings.

Rigidity, adhesion and delamination of the coating in the “substrate - coating” system

Protective coatings are widely used in all branches of production and life. The necessary qualities of coatings are provided by developing complex thin-layer compositions. The complexity of the structure of the coating also arises during operation as a result of the influence of the environment, physical fields, human factor. Many coatings are initially formed directly on the surfaces of structures with initially complex geometry. At the same time, a number of smart coatings, along with a complex structure, change their physical and mechanical properties when triggered. When choosing a coating, adhesive and technology for its application, questions arise related to determining their necessary geometric and physical parameters, assessing their mechanical properties and service life depending on the environment and physical fields, etc. This requires a reliable research tool. In the review, based on well-known publications and patents for the invention, the following are noted: methods for studying the mechanical properties of decomposable and non-decomposable coatings; methods for determining adhesion - the adhesion strength of the coating to the substrate; methods for studying the delamination of constituent elements and delamination of the coating from the substrate. Attention is focused on effective experimental and theoretical methods for assessing the mechanical properties of the coating and adhesive on flat and non-planar surfaces, as well as on some relevant results.

Special Issue: Corrosion Effects and Smart Coatings of Corrosion Protection

Materials that are capable of adapting their properties dynamically to an external stimulus are called stimuli-responsive or “smart materials” [...]

Zeolites as Carriers of Nano-Fertilizers: From Structures and Principles to Prospects and Challenges

The world is facing immense challenges in terms of food security, due to the combined impacts of the ever-increasing population and the adversity of climate change. In an attempt to counteract these factors, smart nutrient delivery systems, including nano-fertilizers, additives, and material coatings, have been introduced to increase food productivity to meet the growing food demand. Use of nanocarriers in agro-practices for sustainable farming contributes to achieving up to 75% nutrient delivery for a prolonged period to maintain nutrient availability in soil for plants in adverse soil conditions. In this context, sieve-like zeolites and the diversity in their structural morphologies have attracted increasing interest over recent years. Engineered nano-porous zeolites, also called aluminosilicates, are defined based on the presence of micro- (<2 nm), meso- (2–50 nm), and macropores (>50 nm), which can be employed as carriers of fertilizers due to their enhanced ion-exchange properties and adsorption capabilities. In this study, we provide a detailed overview of the production and optimization of hierarchical zeolite structures within the size range from micro- to nanometers, as well as the various top-down and bottom-up approaches which have been used to synthesize zeolites with a large surface area, tunable pore size, and high thermal stability, which make them an excellent candidate to be used in agronomy. The delivery of pesticides, insecticides, and fertilizers by loading them into nano-zeolites to manage the crop production without disrupting the soil health is discussed, as well as future perspectives of zeolites in the perpetual maintenance of soil productivity.

Who wins the race near the interface? Stratification of colloids, nano-surfactants, and others

The diffusion of colloids, nanoparticles, and small molecules near the gas–liquid interface presents interesting multiphase transport phenomena and unique opportunities for understanding interactions near the surface and interface. Stratification happens when different species preside over the interfaces in the final dried coating structure. Understanding the principles of stratification can lead to emerging technologies for materials’ fabrication and has the potential to unlock innovative industrial solutions, such as smart coatings and drug formulations for controlled release. However, stratification can be perplexing and unpredictable. It may involve a complicated interplay between particles and interfaces. The surface chemistry and solution conditions are critical in determining the race of particles near the interface. Current theory and simulation cannot fully explain the observations in some experiments, especially the newly developed stratification of nano-surfactants. Here, we summarize the efforts in the experimental work, theory, and simulation of stratification, with an emphasis on bridging the knowledge gap between our understanding of surface adsorption and bulk diffusion. We will also propose new mechanisms of stratification based on recent observations of nano-surfactant stratification. More importantly, the discussions here will lay the groundwork for future studies beyond stratification and nano-surfactants. The results will lead to the fundamental understanding of nanoparticle interactions and transport near interfaces, which can profoundly impact many other research fields, including nanocomposites, self-assembly, colloidal stability, and nanomedicine.

An intelligent icephobic coating based on encapsulated phase change materials (PCM)

The phase change materials (PCMs) have attracted great interest for applications as smart icephobic coatings because of their capability to restore and release energy. PCMs release a large amount of energy as latent heat upon freezing, which is a stimuli-response behavior for anti-icing applications. Such materials embedded within coatings can be applied to exposed infrastructures to protect them against icing. Here, we encapsulated a mixture of PCMs in a urea–formaldehyde (UF) shell by in situ polymerization and then incorporated the microcapsules into a polydimethylsiloxane (PDMS) coating. Microcapsules 5–15 µm in diameter having a shell thickness of about 200 nm were fabricated. Investigating the chemical composition of the fabricated microcapsules confirmed that PCM material was successfully encapsulated within the UF shell. Moreover, the differential scanning calorimetry (DSC) analysis showed that the PCM preserved its phase-change characteristics when encapsulated and embedded within the matrix. Increasing the abundance of microcapsules within the coating lowered the ice nucleation temperature, verified by DSC, and increased the freezing-delay time because of PCM latent heat release. We utilized a custom-made apparatus, called micro-push-off set-up that allowed us to measure ice adhesion at the exact moment that the water droplet was completely frozen. Therefore, it was observed that the presence of the PCM microcapsules reduced ice adhesion strength, through either possible mechanism of the formation of quasi-liquid layer (QLL) or thermal expansion differences. Furthermore, lower ice adhesion resulted in reduced ice accumulation on the PCM-containing coatings, verified by the static accumulation test (SAT).

Regenerable bacterial killing–releasing ultrathin smart hydrogel surfaces modified with zwitterionic polymer brushes

Abstract Building long-lasting antimicrobial and clean surfaces is one of the most effective strategies to inhibit bacterial infection, but obtaining an ideal smart surface with highly efficient, controllable, and regenerative properties still encounters many challenges. Herein, we fabricate an ultrathin brush–hydrogel hybrid coating (PSBMA-P(HEAA-co-METAC)) by integrating antifouling polyzwitterionic (PSBMA) brushes and antimicrobial polycationic (P(HEAA-co-METAC)) hydrogels. The smart bacterial killing–releasing properties can be achieved independently by the opposite volume and conformation changes between the swelling (shrinking) of P(HEAA-co-METAC) hydrogel layer and the shrinking (swelling) of PSBMA brushes. The friction test reveals that both METAC and SBMA components support great lubrication. By tuning the initial organosilane (BrTMOS:KH570) ratios, the prepared PSBMA-P(HEAA-co-METAC) coating exhibits different antibacterial abilities from single “capturing–killing” to versatile “capturing–killing–releasing.” Most importantly, 99% of the bacterial-releasing rate can be easily achieved via 0.5 M NaCl treatment. This smart surface not only possesses long-lasting antibacterial performance, only ∼1.09 × 105 cell·cm−2 bacterial residue even after 72 h exposure to bacteria solutions, but also can be regenerated and triggered between water and salt solution multiple times. This work provides a new way to fabricate antibacterial smart hydrogel coatings with bacterial “killing–releasing” functions and shows great potential for biomedical applications.

Synergistic Behavior of Polyethyleneimine and Epoxy Monomers Loaded in Mesoporous Silica as a Corrosion-Resistant Self-Healing Epoxy Coating.

Corrosion is a significant problem and is, to a large extent, responsible for the degradation of metallic parts. In this direction, mesoporous silica particles (MSPs) were synthesized by a sol–gel technique and had an average pore diameter of ∼6.82 nm. The MSPs were loaded with polyethyleneimine (PEI) and epoxy monomers and, after that, carefully mixed into the epoxy matrix to formulate new modified polymeric coatings. The microstructural, compositional, structural, and thermal properties were investigated using various characterizing tools [Transmission electron microscopy, Fourier transform infrared spectroscopy, hermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy]. TGA confirms the loading of mesoporous silica with a corrosion inhibitor, and its estimated loading amount is ∼8%. The electrochemical impedance spectroscopy properties of the reference and modified coated samples confirm the promising anti-corrosive performance of the synthesized polymeric smart coatings. Localized electrochemical tests (scanning vibrating electrode technique and scanning ion-selective electrode technique) evidence the corrosion inhibition ability of the coating, and its self-healing was also observed during 24 h of immersion. The decent anti-corrosion performance of the modified coatings can be credited to the efficient synergistic effect of the PEI and epoxy monomer.

Smart Anticorrosion Coatings Based on Poly(phenylene methylene): An Assessment of the Intrinsic Self-Healing Behavior of the Copolymer.

Poly(phenylene methylene) (PPM) is a multifunctional polymer featuring hydrophobicity, high thermal stability, fluorescence and thermoplastic processability. Accordingly, smart corrosion resistant PPM-based coatings (blend and copolymer) were prepared and applied by hot pressing on aluminum alloy AA2024. The corrosion protection properties of the coatings and their dependence on coating thickness were evaluated for both strategies employed. The accelerated cyclic electrochemical technique (ACET), based on a combination of electrochemical impedance spectroscopy (EIS), cathodic polarizations and relaxation steps, was used as the main investigating technique. At the coating thickness of about 50 µm, both blend and copolymer PPM showed effective corrosion protection, as reflected by |Z|0.01Hz of about 108 Ω cm2 over all the ACET cycles. In contrast, when the coating thickness was reduced to 30 µm, PPM copolymer showed neatly better corrosion resistance than blended PPM, maintaining |Z|0.01Hz above 108 Ω cm2 with respect to values below 106 Ω cm2 of the latter. Furthermore, the analysis of many electrochemical key features, in combination with the optical investigation of the coating surface under 254 nm UV light, confirms the intrinsic self-healing ability of the coatings made by PPM copolymer, contrary to the reference specimen (i.e., blend PPM).

Investigation of intelligent protection and corrosion detection of epoxy-coated St-12 by redox-responsive microcapsules containing dual-functional 8-hydroxyquinoline

Smart coatings with self-healing capabilities have frequently been made using microcapsules. Incorporating bifunctional materials as a self-healing agent into microcapsules allows for the early detection of corrosion before substantial damage to the metal surface occurs. In this study, the oxidative polymerization of aniline in the direct miniemulsion method was used to synthesize polyaniline (PANI) microcapsules. The corrosion inhibitor 8-hydroxyquinoline (8-HQ) was used in the core of microcapsules, which can also act as a fluorescent indicator of iron ions. The synthesized microcapsules were characterized by Optical Microscopic (OM), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared (FTIR), Ultraviolet-Visible (UV–Vis), and Dynamic Light Scattering (DLS) techniques. The corrosion resistance behavior and self-healing performance of 8-hydroxyquinoline loaded polyaniline microcapsules into epoxy coating were investigated by Electrochemical Impedance Spectroscopy (EIS), and standard salt spray test. It was found that the epoxy coating containing 5 wt% of the polyaniline microcapsules with 1000 ppm of encapsulated 8-hydroxyquinoline exhibited better corrosion protection performance with an impedance value of 1.54 × 108 Ω.cm2 at low frequency (0.01 Hz) out of all the samples after 10 weeks immersion in electrolyte with a concentration of 3.5 wt% NaCl. Additionally, the evaluation of the release of 8-hydroxyquinoline from microcapsules in a damaged area is characterized by Inductively Coupled Plasma (ICP) spectrometer and fluorescence microscope. The synergistic effects of polyaniline microcapsules and the 8-hydroxyquinoline healing agent are thus responsible for the coatings' self-healing abilities. The study's findings revealed that the dual-functional 8-hydroxyquinoline is successfully released from the microcapsules and acts as a fluorescent indicator and corrosion inhibitor by detecting corrosion at the early stages.

A Robust Superhydrophobic Smart Coating with Reversible Thermochromic and Photochromic Property

Both thermochromic and photochromic coating have attracted many attentions due to their widely applications, but the low stability is a big obstacle. Inspired by the lotus leaf, to endow the chromic coating with superhydrophobicity is a possible solution. In this research, a dual response coating was prepared by adding photochromic and thermochromic particles simultaneously. The prepared sample demonstrated at least four-state color switching, which can be successfully used in tactile imaging, multi-color fabric, erasable record, and security labels. The superhydrophobicity was achieved by introducing vinyl-terminated polydimethylsiloxane, which not only offers low surface energy but also can cross-link with the particles to increase the adhesion. Thus, the prepared sample maintained superhydrophobicity after various kinds of destruction (such as sandpaper abrasion, corrosive liquid attack, ultrasonic treatment, UV irradiation, and high-speed drops/turbulent jets impact). Even though the superhydrophobicity can be destroyed by plasma etching, it can be recovered after 12 h at room temperature.