Redox-responsive self-healing for corrosion protection

Developments in anticorrosive organic coatings modulated by nano/microcontainers with porous matrices

The durability and functionality of many metallic structures are seriously threatened by corrosion, which makes the development of anticorrosive coatings imperative. This state-of-the-art survey explores the recent developments in the field of anticorrosive organic coatings modulated by innovations involving nano/microcontainers with porous matrices. The integration of these cutting-edge delivery systems seeks to improve the protective properties of coatings by enabling controlled release, extended durability, targeted application of corrosion inhibitors, and can be co-constructed to achieve defect filling by polymeric materials. The major highlight of this review is an in-depth analysis of the functionalities provided by porous nano/microcontainers in the active protection and self-healing of anticorrosive coatings, including their performance evaluation. In one case, after 20 days of immersion in 0.1 M NaCl, a scratched coating containing mesoporous silica nanoparticles loaded with an inhibitor benzotriazole and shelled with polydopamine (MSNs-BTA@PDA) exhibited coating restoration indicated by a sustained corrosion resistance rise over an extended period monitored by impedance values at 0.01 Hz frequency, rising from 8.3 × 104 to 7.0 × 105 Ω cm2, a trend assigned to active protection by the release of inhibitors and self-healing capabilities. Additionally, some functions related to anti-fouling and heat preservation by nano/microcontainers are highlighted. Based on the literature survey, some desirable properties, current challenges, and prospects of anticorrosive coatings doped with nano/microcontainers have been summarized. The knowledge gained from this survey will shape future research directions and applications in a variety of industrial areas, in addition to advancing smart corrosion prevention technology.

Self-healing, antibiofouling and anticorrosion properties enabled by designing polymers with dynamic covalent bonds and responsive linkages

Coating metal structures with a protective material is a popular strategy to prevent their deterioration due to corrosion. However, maintaining the barrier properties of coatings after their mechanical damage is challenging. Herein, we prepared multifunctional coatings with self-healing ability to conserve their anticorrosion performance after damage. The coating was formed by blending synthesized redox-responsive copolymers with the ability to release a corrosion inhibitor upon the onset of corrosion with synthesized self-healing polyurethanes containing disulfide bonds. The corrosion rate of steel substrates coated with a blend is approximately 24 times lower than that of steel coated with only self-healing polyurethane. An exceptional healing efficiency, as high as 95%, is obtained after mechanical damage. The antibiofouling property against bacterial and microalgal attachments on coatings is facilitated by the repellent characteristic of fluorinated segments and the biocidal activity of the inhibitor moieties in the copolymer.

Superhydrophobic Polyaniline-Siloxane Coatings with Excellent Barrier and Active Corrosion Protection Properties for Mild Steel

Although superhydrophobic surfaces have attracted much attention in research, their high cost, poor durability, and challenging manufacturing processes have prevented their widespread application. Here, we describe a simple method of preparing superhydrophobic polyaniline (PANI) pigments and their application in protective coatings. Doping polyaniline pigments with low surface energy perfluorodecanoic acid (PFDA) allowed them to overcome their intrinsic high surface energy, and the resultant PANI-PFDA pigments showed superhydrophobicity. The superhydrophobic PANI-PFDA pigments with different weight percentages were incorporated into a polydimethylsiloxane (PDMS) coating to prepare the superhydrophobic coating. We endeavored to examine the role that hydrophobicity played in enhancing corrosion resistance and looked into the highest concentration of pigment that the coating could withstand. Additionally, studies were carried out on the coating's adherence to the metal and the stability of hydrophobicity at various pH levels. The results showed that PANI-PFDA pigments improved the hydrophobicity and corrosion resistance in the PDMS coating without compromising its robustness and durability. Electrochemical impedance spectroscopy studies revealed that 40 wt % PANI-PFDA content in the PDMS coating provided the best corrosion protection, and this coating could offer active corrosion protection when an artificial defect was made in the coating.

Corrosion-Responsive Self-Healing Coatings

Organic coatings are one of the most popular and powerful strategies for protecting metals against corrosion. They can be applied in different ways, such as by dipping, spraying, electrophoresis, casting, painting, or flow coating. They offer great flexibility of material designs and cost effectiveness. Moreover, self-healing has evolved as a new research topic for protective organic coatings in the last two decades. Responsive materials play a crucial role in this new research field. However, for targeting the development of high-performance self-healing coatings for corrosion protection, it is not sufficient just to focus on smart responsive materials and suitable active agents for self-healing. A better understanding of how coatings can react on different stimuli induced by corrosion, how these stimuli can spread in the coating, and how the released agents can reach the corroding defect is also of high importance. Such knowledge would allow the design of coatings that are optimized for specific applications. Herein, the requirements and possibilities from the corrosion and synthesis perspectives for designing materials for preparing self-healing coatings for corrosion protection are discussed.

Double Stimuli-Responsive Conducting Polypyrrole Nanocapsules for Corrosion-Resistant Epoxy Coatings

Stimuli-responsive nanocapsules, which can respond to various environmental stimuli and release their encapsulated payload on demand, have attracted wide interest in different fields in recent years. In this work, a novel kind of polypyrrole (PPy) nanocapsules is fabricated and loaded with zinc salt corrosion inhibitors. The synthesized PPy nanocapsules respond to two different external stimuli (pH- and redox-responsive) and can control the release of their encapsulated corrosion inhibitors. The nanocapsules can detect the micro-environmental pH or surface-potential changes associated with the corrosion initiation of the metal substrate. When introduced into a protective epoxy coating, the fabricated PPy nanocapsules inhibit the anodic and cathodic corrosion reactions. The superior corrosion resistance and active corrosion protection effects of the epoxy-PPy-Zn coatings are further demonstrated via electrochemical and long-term immersion tests. The low-frequency impedance, coating resistance, and oxide film resistance increase after about 400 h of exposure in a 3.5 wt % NaCl solution, reflecting the enhanced corrosion protection properties and excellent repairing performance of the coating. Furthermore, the epoxy-PPy-Zn coating can avoid the pitting corrosion of 304 stainless steel. Overall, we have fabricated double stimuli-responsive PPy nanocapsules via a simple and effective strategy and incorporated them into a corrosion-resistant epoxy coating for protecting Fe-based metal substrates.

Metal organic frameworks (MOFs) as multifunctional nanoplatform for anticorrosion surfaces and coatings

Corrosion of metallic materials is a long-standing problem in many engineering fields. Various organic coatings have been widely applied in anticorrosion of metallic materials over the past decades. However, the protective performance of many organic coatings is limited due to the undesirable local failure of the coatings caused by micro-pores and cracks in the coating matrix. Recently, metal organic frameworks (MOFs)-based surfaces and coatings (MOFBSCs) have exhibited great potential in constructing protective materials on metallic substrates with efficient and durable anticorrosion performance. The tailorable porous structure, flexible composition, numerous active sites, and controllable release properties of MOFs make them an ideal platform for developing various protective functionalities, such as self-healing property, superhydrophobicity, and physical barrier against corrosion media. MOFs-based anticorrosion surfaces and coatings can be divided into two categories: the composite surfaces/coatings using MOFs-based passive/active nanofillers and the surfaces/coatings using MOFs as functional substrate support. In this work, the state-of-the-art fabrication strategies of the MOFBSCs are systematically reviewed. The anticorrosion mechanisms of MOFBSCs and functions of the MOFs in the coating matrix are discussed accordingly. Additionally, we highlight both traditional and emerging electrochemical techniques for probing protective performances and mechanisms of MOFBSCs. The remaining challenging issues and perspectives are also discussed.

Bioinspired micro/nano structured aluminum with multifaceted applications

Inspired by many biological systems such as lotus leaves, insect wings and rose petals, great attention has been devoted to the study and fabrication of artificial superhydrophobic surfaces with multiple functionalities. In the present study, a simple and ecological synthesis route has been employed for large scale fabrication of self-assembled, sustainable nanostructures on unprocessed and micro imprinted aluminum surfaces named 'Nano' and 'Hierarchy'. The processed samples show extreme wettability ranging from superhydrophilicity to superhydrophobicity depending on post-processing conditions. The densely packed ellipsoidal nanostructures exhibited superhydrophobicity with excellent water, bacterial and dust repellency when modified by low surface energy material 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FOTES), characterized by a static contact angle of 163 ± 1° and contact angle hysteresis (CAH) ~3°. These coated surfaces show significant corrosion resistance with current density of 6 nA/cm² which is 40 times lower than unprocessed counterpart and retain chemical stability after prolonged immersion in corrosive media. These surfaces show excellent self-cleaning ability with significantly low water consumption (< 0.1 µl/mm²-mg) and prevent biofouling which ensures its applicability in biological environment and marine components. The nanostructured superhydrophilic aluminum shows maximum antibacterial activity due to disruption of cell membrane. This work can offer a simple strategy to large scale fabrication of multifunctional biomimetic metallic surfaces.

Self-Assembly of Graphene Oxide Nanoflakes in a Lipid Monolayer at the Air-Water Interface

The graphene family, especially graphene oxide (GO), has captured increasing prospects in the biomedical field due to its excellent physicochemical properties. Understanding the health and environmental impact of GO is of great importance for guiding future applications. Although their interactions with living organisms are omnipresent, the exact molecular mechanism is yet to be established. The cellular membrane is the first barrier for a foreign molecule to interact before entering into the cell. In the present study, a model system consisting of a lipid monolayer at the air-water interface represents one of the leaflets of this membrane. Surface pressure-area isotherms and advanced synchrotron X-ray scattering techniques have been employed to comprehend the interaction by varying the electrostatics of the membrane. The results depict a strong GO interaction with positively charged phospholipids, weak interaction with zwitterionic lipids, and interestingly negligible interaction with negatively charged lipids. GO flakes induce significant changes in the out-of-plane organization of a positively charged lipid monolayer with a minor influence on in-plane assembly of lipid chains. This interaction is packing-specific, and the influence of GO is much stronger at lower surface pressure. Even though for zwitterionic phospholipids, the GO flakes may partly insert into the lipid chains, the X-ray scattering results indicate that the flakes preferentially lie horizontally underneath the positively charged lipid monolayer. This in-depth structural description may pave new perspectives for the scientific community for the development of GO-based biosensors and biomedical materials.

Design of Nanostructured Protective Coatings with a Sensing Function

Nanostructured multilayered coatings for metals are prepared to simultaneously provide a function of corrosion mitigation and of corrosion sensing for copper substrates. Silica nanocapsules, embedded in one layer of the coating, are used as a host for a corrosion inhibitor and as a sensor, which detect changes of pH value and release inhibitors via an optical signal. Furthermore, another layer in the coating exists in a nanonetwork loaded with another corrosion inhibitor, which is impregnated with a hydrophobic polymer. We demonstrate that a specific arrangement of layers leads to an optimum anticorrosion and sensing performance while the sensing signal can be prolonged for a long time. It is the first time that the fluorophore detecting corrosion is conjugated to the nanosensor and that nanofibers and nanocapsules are used simultaneously to load and release corrosion inhibitors for anticorrosion applications.

Self-Healable Superomniphobic Surfaces for Corrosion Protection

Corrosion-protective surfaces are of the utmost relevance to ensure long-term stability and reliability of metals and alloys by limiting their interactions with corrosive species, such as water and ions. However, their practical applications are often limited either by the inability to repel low surface tension liquids such as oils and alcohols or by poor mechanical durability. Here, a superomniphobic surface is reported that can display very high contact angles for both high and low surface tension liquids as well as for concentrated acids and bases. Such extreme repellency allowed for approximately 20% of the corrosion rate compared to the conventional superhydrophobic corrosion protective coatings. Furthermore, the superomniphobic surface can autonomously repair mechanical damage at an elevated temperature (60 °C) within a short period of time (60 s), and the surface can restore its intrinsic corrosion protection performance. Such superomniphobic surfaces thus offer a wide range of potential applications, including pipelines, with sustainable corrosion protection and rust inhibitors for steel in reinforced concrete.

Nanocontainer-Based Active Systems: From Self-Healing Coatings to Thermal Energy Storage

We highlight the development of nanocontainer-based active materials started in 2006 at the Max Planck Institute of Colloids and Interfaces under the supervision of Prof. Helmuth Möhwald. The active materials encapsulated in the nanocontainers with controlled shell permeability have been first applied for self-healing coatings with controlled release of the corrosion inhibitor. The nanocontainers have been added to the paint formulation matrix at 5-10 wt % concentration, which resulted in attaining a coating-autonomous self-healing ability. This research idea has attracted the attention of many scientists around the world (>1500 publications during the last 10 years) and has already been transferred to the commercialization level. The current trend in nanocontainer-based active systems is devoted to the multifunctionality of the capsules which can combine self-healing, antibacterial, thermal, and other functionalities into one host matrix. This article summarizes the previous research done in the area of nanocontainer-based active materials together with future perspectives of capsule-based materials with antifouling or thermoregulating activity.

Mannich Base as Corrosion Inhibitors for N80 Steel in a CO₂ Saturated Solution Containing 3 wt % NaCl

In this paper, a corrosion inhibitor containing nitrogen atoms and a conjugated π bond was synthesised, and its final product synthesised by the optimal conditions of the orthogonal test results is named multi-mannich base (MBT). The corrosion inhibition effect on the N80 steel sheet of the corrosion inhibitor was evaluated in a CO₂ saturated solution containing 3 wt % NaCl; the corrosion rate was 0.0446 mm/a and the corrosion inhibition rate was 90.4%. Through electrochemical and adsorption theory study, MBT is a mixed corrosion inhibitor that mainly shows cathode suppression capacity. The adsorption of MBT on the surface of the steel sheet follows the Langmuir adsorption isotherm; it can be spontaneously adsorbed on the surface of the N80 steel sheet, which has a good corrosion inhibition effect. The surface of the N80 steel sheet was microscopically characterised by atomic force microscope (AFM). It can be seen from the results that the N80 steel sheet with MBT added is significantly different from the blank control group; the surface of the steel sheet is relatively smooth, indicating that MBT forms an effective protective film on the surface of N80 steel, which inhibits the steel sheet.

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.

Pretreatment with a β-Cyclodextrin-Corrosion Inhibitor Complex Stops an Initiated Corrosion Process on Zinc

Metal pretreatment is typically the first step in a reliable corrosion protection system. This work explores the incorporation of complexes between the cyclic oligosaccharide β-cyclodextrin (β-CD) and the molecular organic corrosion inhibitor 2-mercaptobenzothiazole (MBT) into an oxide-based pretreatment layer on metallic zinc. The layers were produced by a precorrosion step in the presence of β-CD. The resulting films have a morphology dominated by spherical particles. X-ray photoelectron spectroscopy investigations of the surfaces show the sulfur atoms of MBT to be partially oxidized but mostly intact. Samples pretreated with such a layer were subsequently coated with a model polymer coating, and the delamination of this model coating from an artificial defect was monitored by a scanning Kelvin probe (SKP). The SKP results show a slow down of delamination after several hours of the ongoing corrosion process for surfaces pretreated with the complexes. Finally, an increase in the electrode potential in the defect was observed, with a subsequent complete stop in delamination and repassivation of the defect after ≈10 h. This repassivation is attributed to the release of MBT after the initiation of the corrosion process. Most likely, the increase of pH, combined with the availability of aqueous solution, facilitates the MBT release after the initiation of a corrosion process. Consequently, complexes formed from β-CD and corrosion inhibitors can be effectively incorporated into inorganic pretreatments, and the inhibitor component can be released upon start of the corrosion process.

Nanocontainer-based self-healing coatings: current progress and future perspectives

Nanocontainers add more functionalities to the standard coating formulations.

Synthesis of calcium carbonate microcapsules as self-healing containers

Contemporary studies of self-healing polymer composites are based on microcapsules synthesized using synthetic and toxic polymers, biopolymers, etc. via methods such as in situ polymerization, electrospraying, and air atomization. Herein, we synthesized a healing agent, epoxy (EPX) encapsulated calcium carbonate (CC) microcapsules, which was used to prepare self-healing EPX composites as a protective coating for metals. The CC microcapsules were synthesized using two facile methods, namely, the soft-template method (STM) and the in situ emulsion method (EM). Microcapsules prepared using the STM (ST-CC) were synthesized using sodium dodecyl sulphate (SDS) surfactant micelles as the soft-template, while the microcapsules prepared using the EM (EM-CC) were synthesized in an oil-in-water (O/W) in situ emulsion. These prepared CC microcapsules were characterized using light microscopy (LMC), field emission scanning electron microscopy (FE-SEM), fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), and thermogravimetric analysis (TGA). The synthesized ST-CC microcapsules were spherical in shape, with an average diameter of 2.5 μm and an average shell wall thickness of 650 nm, while EM-CC microcapsules had a near-spherical shape with an average diameter of 3.4 μm and an average shell wall thickness of 880 nm. The ST-CC capsules exhibited flake-like rough surfaces while EM-CC capsules showed smooth bulgy surfaces. The loading capacity of ST-CC and EM-CC microcapsules were estimated using TGA and found to be 11% and 36%, respectively. The FTIR and NMR spectra confirmed the EPX encapsulation and the unreactive nature of the loaded EPX with the inner walls of CC microcapsules. The synthesized CC microcapsules were further incorporated into an EPX matrix to prepare composite coatings with 10 (w/w%), 20 (w/w%), and 50 (w/w%) capsule loadings. The prepared EPX composite coatings were scratched and observed using FE-SEM and LMC to evaluate the release of encapsulated EPX inside the CC capsules, which is analogous to the healing behaviour. Moreover, EPX composite coatings with 20 (w/w%) and 50 (w/w%) of ST-CC showed better healing performances. Thus, it was observed that ST-CC microcapsules outperformed EM-CC. Additionally, the EPX/CC coatings showed remarkable self-healing properties by closing the gaps of the scratch surfaces. Thus, these formaldehyde-free, biocompatible, biodegradable, and non-toxic CC based EPX composite coatings hold great potential to be used as a protective coating for metal substrates. Primary results detected significant corrosion retardancy due to the self-healing coatings under an accelerated corrosion process, which was performed with a salt spray test.

Healing agent, epoxy encapsulated calcium carbonate microcapsules were prepared using a facile method as a self-healing composite for protective metal coatings.

Graphene oxide encapsulated by mesoporous silica for intelligent anticorrosive coating: studies on release models and self-healing ability

The efficient release of benzotriazole from an insulating graphene/mesoporous silica nanoreservoir inspired us to fabricate a bi-layered anticorrosive coating with self-healing ability at the functional level.

High Performance Anti-Corrosion Coatings of Poly (Vinyl Butyral) Composites with Poly N-(vinyl)pyrrole and Carbon Black Nanoparticles

Zinc is widely used in battery negative electrodes and steel coatings for automotive industries. The anti-corrosion property of zinc is the most important factor determining the performance and lifetime of the products. In this paper, both size-controlled poly N-(vinyl)pyrrole (PNVPY) nanoparticles and carbon black (CB) nanoparticles were compounded with poly (vinyl butyral) (PVB) binder developing a series of composite coatings covered on the zinc substrates using a spin-coating technique. The morphologies of the surface and cross section of the PNVPY/CB/PVB coatings indicate that the PNVPY and CB nanoparticles are uniformly distributed in the matrix. The corrosion resistance of the composite coatings was tested by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in a 3.5% NaCl solution. It is found that the coating with 1.9 wt.% PNVPY and 2.3 wt.% CB nanoparticles shows a remarkably high resistance value (R_c) and corrosion protection efficiency (99.99%). Meanwhile, the immersion results also reveal its superior corrosion resistance. It is considered that the nanoscale dispersion of PNVPY and carbon in PVB matrix and the strong interface action between the nanoparticles and PVB result in the uniform microstructure of the composites which endues the superior corrosion properties of the coatings.

Self-Protecting Epoxy Coatings with Anticorrosion Microcapsules

The corrosion of steel substrates causes damage that is costly to repair or replace. Current protective coatings predominately rely on environmentally harmful anticorrosive agents and toxic solvents to protect the underlying substrate. The use of lawsone (2-hydroxy-1,4-napthoquinone) together with a water-based epoxy coating provides an environmentally friendly alternative for common protective coatings. Microencapsulated lawsone embedded in an epoxy coating allows the anticorrosive agent to remain dormant until released by damage and delivered directly onto the steel substrate. UV-vis analysis confirms successful encapsulation of lawsone in a polyurethane shell wall and reveals up to 8 wt % lawsone in the capsule cores. Uniform dry film thickness and inflicted damaged are verified with ultrasound and optical microscopy. Visual and electrochemical analysis demonstrates that this self-protective scheme leads to a 70% corrosion inhibition efficiency in a neutral salt water solution.

Hierarchical, Self-Healing and Superhydrophobic Zirconium Phosphate Hybrid Membrane Based on the Interfacial Crystal Growth of Lyotropic Two-Dimensional Nanoplatelets

We demonstrate a facile route to in situ growth of lyotropic zirconium phosphate (ZrP) nanoplates on textiles via an interfacial crystal growing process. The as-prepared hybrid membrane shows a hierarchical architecture of textile fibers (porous platform for fluid transport), ZrP nanoplatelets (layered scaffolds for chemical barriers), and octadecylamine (organic species for superhydrophobic functionalization). Interestingly, such a hybrid membrane is able to separate the oily wastewater with a high separation efficiency of 99.9%, even at in harsh environments. After being chemically etched, the hybrid membrane is able to restore its hydrophobicity autonomously and repeatedly, owing to the hierarchical structure that enables facile loading of healing agent. We anticipate that the concept of implanting superhydrophobic self-healing features in anisotropic structure of lyotropic nanoparticles will open up new opportunities for developing advanced multifunctional materials for wastewater treatment, fuel purification, and oil spill mitigation.

Redox-Responsive Polymer with Self-Immolative Linkers for the Release of Payloads

Previous couplings of corrosion inhibitors to redox-responsive polymers via covalent bonding suffer from several drawbacks. It is presented here novel redox-responsive polymer-corrosion inhibitor conjugates that contain self-immolative linkers in their side chains. Very fast redox-induced release of tryptamine, a drug and a corrosion inhibitor, is observed after applying a reductive trigger.

Design and Fabrication of a Novel Stimulus-Feedback Anticorrosion Coating Featured by Rapid Self-Healing Functionality for the Protection of Magnesium Alloy

Corrosion potential stimulus-responsive smart nanocontainers (CP-SNCs) are designed and synthesized based on the installation of the supramolecular assemblies (bipyridinium ⊂ water-soluble pillar[5]arenes) onto the exterior surface of magnetic nanovehicles (Fe₃O₄@mSiO₂), linked by disulfide linkers. The supramolecular assemblies with high binding affinity as gatekeepers effectively block the encapsulated organic corrosion inhibitor, 8-hydroxyquinoline (8-HQ), within the mesopores of Fe₃O₄@mSiO₂. When the corrosion potential of the magnesium alloy (-1.5 V vs SHE) is exerted, 8-HQ is released instantly because of the cleavage of disulfide linkers and the removal of the supramolecular assemblies. CP-SNCs were incorporated into the hybrid organic-inorganic sol-gel coating to construct a corrosion potential stimulus-feedback anticorrosion coating (CP-SFAC) that was then deposited on the magnesium alloy, AZ31B. With the aid of a magnetic field, CP-SNCs were gathered in the proximity of the surface of AZ31B. CP-SFAC showed a satisfactory anticorrosion performance, more importantly, through the evaluation of microzone electrochemical techniques. CP-SFAC presented the rapid self-healing functionality when the localized corrosion occurred. Shortening the distance between CP-SNCs and the surface of AZ31B enhances the availability of the incorporated CP-SNCs and makes most of the CP-SNCs to timely respond to the corrosion potential stimulus and facilitates the formation of a compact molecular protective film before the corrosion products pile up. The characteristics of fast response time and quick self-healing rate meet the requirements of the magnesium alloy for self-healing in local regions.

A Novel Eco-Friendly Scale and Corrosion Inhibitor Modified by β-Cyclodextrin

A polymer, β-MEA, was synthesised from β-cyclodextrin (β-CD), 3-chloro-2-methylpropene (MAC), epoxysuccinic acid (ESA), and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) with a (NH4)2S2O8-NaHSO3 redox initiator system by aqueous solution radical polymerisation. β-MEA was characterised by means of IR spectroscopy, time-of-flight mass spectrometry, gel permeation chromatography, and thermogravimetric analysis. Its structure, molecular weight, thermal stability, scale and corrosion inhibition performance and mechanism were investigated. The results verified that β-MEA achieves a better scale inhibition efficiency for BaSO4 compared with poly(aspartic acid) (PASP) (100 % cf. 94.9 % at a concentration of 20 mg L−1) and a better corrosion inhibition efficiency of N80 carbon steel in saline water compared with PESA (91.2 % cf. 79.7 % at a concentration of 1 g L−1). The BaSO4 was characterised by scanning electron microscopy (SEM) and X-ray diffraction to investigate the crystal morphology of the scale. Primary research on the mechanism for corrosion inhibition was carried by SEM-chemical analysis.

Redox-responsive release of active payloads from depolymerized nanoparticles

The difference in the reactivity of two monomers, aniline (ANI) and 2,5-dimercapto-1,3,4-thiadiazole (DMcT), was employed to design nanoparticles with completely different nanostructures.

Facile Synthesis of Smart Nanocontainers as Key Components for Construction of Self-Healing Coating with Superhydrophobic Surfaces

SiO2-imidazoline nanocomposites (SiO2-IMI) owning high loading capacity of corrosion inhibitor, 1-hexadecyl-3-methylimidazolium bromide (HMID), and a special acid/alkali dual-stimuli-accelerated release property have been synthesized via a one-step modified Stöber method. SiO2-IMI were uniformly distributed into the hydrophobic SiO2 sol to construct "host"-"guest" feedback active coating with a superhydrophobic surface (SiO2-IMI@SHSC) on aluminium alloy, AA2024, by dip-coating technique. SiO2-IMI as "guest" components have good compatibility with "host" sol-gel coating, and more importantly, once localized corrosion occurs on the surface of AA2024, SiO2-IMI can simultaneously respond to the increase in environmental pH around corrosive micro-cathodic regions and decrease in pH near micro-anodic regions, promptly releasing HMID to form a compact molecular film on the damaged surface, inhibiting corrosion spread and executing a self-healing function. The scanning vibrating electrode technique (SVET) was applied to illustrate the suppression process of cathodic/anodic corrosion activities. Furthermore, benefiting from the superhydrophobic surface, SiO2-IMI@SHSC remained its protective ability after immersion in 0.5 M NaCl solution for 35 days, which is far superior to the conventional sol-gel coating with the same coating thickness. The facile fabrication method of SiO2-IMI simplifies the construction procedure of SiO2-IMI@SHSC, which have great potential to replace non-environmental chromate conversion coatings for practical use.

Electrosprayed Multi-Core Alginate Microcapsules as Novel Self-Healing Containers

Alginate microcapsules containing epoxy resin were developed through electrospraying method and embedded into epoxy matrix to produce a capsule-based self-healing composite system. These formaldehyde free alginate/epoxy microcapsules were characterized via light microscope, field emission scanning electron microscope, fourier transform infrared spectroscopy and thermogravimetric analysis. Results showed that epoxy resin was successfully encapsulated within alginate matrix to form porous (multi-core) microcapsules with pore size ranged from 5–100 μm. The microcapsules had an average size of 320 ± 20 μm with decomposition temperature at 220 °C. The loading capacity of these capsules was estimated to be 79%. Under in situ healing test, impact specimens showed healing efficiency as high as 86% and the ability to heal up to 3 times due to the multi-core capsule structure and the high impact energy test that triggered the released of epoxy especially in the second and third healings. TDCB specimens showed one-time healing only with the highest healing efficiency of 76%. The single healing event was attributed by the constant crack propagation rate of TDCB fracture test. For the first time, a cost effective, environmentally benign and sustainable capsule-based self-healing system with multiple healing capabilities and high healing performance was developed.

Osmotic pressure-dependent release profiles of payloads from nanocontainers by co-encapsulation of simple salts

The encapsulation of payloads in micro- to nano-scale capsules allows protection of the payload from the surrounding environment and control of its release profile. Herein, we program the release of hydrophilic payloads from nanocontainers by co-encapsulating simple inorganic salts for adjusting the osmotic pressure. The latter either leads to a burst release at high concentrations of co-encapsulated salts or a sustained release at lower concentrations. Osmotic pressure causes swelling of the nanocapsule's shell and therefore sustained release profiles can be adjusted by crosslinking it. The approach presented allows for programing the release of payloads by co-encapsulating inexpensive salts inside nanocontainers without the help of stimuli-responsive materials.

Tailoring nanoarchitectonics to control the release profile of payloads

We demonstrate here that the control over the release rate of payloads and on the selectivity of the release can be achieved by designing nanomaterials with a hierarchical structure. Redox-responsive silica nanocapsules are first synthesized to allow for an accelerated release of the corrosion inhibitor 2-mercaptobenzothiazole as a payload upon chemical reduction and retarded release upon oxidation. In a second step, we embedded the nanocapsules into nanofibers by colloid-electrospinning, yielding a hierarchical composite structure. Remarkably, the encapsulation of the nanocapsules in the fibers provides two decisive advantages that are a higher selectivity of the release and a higher control over the release rate of payloads.

Nanocontainers in and onto Nanofibers

Hierarchical structure is a key feature explaining the superior properties of many materials in nature. Fibers usually serve in textiles, for structural reinforcement, or as support for other materials, whereas spherical micro- and nanoobjects can be either highly functional or also used as fillers to reinforce structure materials. Combining nanocontainers with fibers in one single object has been used to increase the functionality of fibers, for example, antibacterial and thermoregulation, when the advantageous properties given by the encapsulated materials inside the containers are transferred to the fibers. Herein we focus our discussion on how the hierarchical structure composed of nanocontainers in nanofibers yields materials displaying advantages of both types of materials and sometimes synergetical effects. Such materials can be produced by first carefully designing nanocontainers with defined morphology and chemistry and subsequently electrospinning them to fabricate nanofibers. This method, called colloid-electrospinning, allows for marrying the properties of nanocontainers and nanofibers. The obtained fibers could be successfully applied in different fields such as catalysis, optics, energy conversion and production, and biomedicine. The miniemulsion process is a convenient approach for the encapsulation of hydrophobic or hydrophilic payloads in nanocontainers. These nanocontainers can be embedded in fibers by the colloid-electrospinning technique. The combination of nanocontainers with nanofibers by colloid-electrospinning has several advantages. (1) The fiber matrix serves as support for the embedded nanocontainers. For example, through combining catalysts nanoparticles with fiber networks, the catalysts can be easily separated from the reaction media and handled visually. This combination is beneficial for the reuse of the catalyst and the purification of products. (2) Electrospun nanofibers containing nanocontainers offer the active agents inside the nanocontainers a double protection by both the fiber matrix and the nanocontainers. Since the polymer of the fibers and the polymer of the nanocontainers have usually opposite polarities, the encapsulated substance, for example, catalysts, dyes, or drugs, can be protected against a large variety of environmental influences. (3) Electrospun nanofibers exhibit unique advantages for tissue engineering and drug delivery that are a structural similarity to the extracellular matrix of biological tissues, large specific surface area, high and interconnected porosity which enhances cell adhesion, proliferation, drug loading, and mass transfer properties, as well as the flexibility in selecting the raw materials. Moreover, the nanocontainer-in-nanofiber structure allows multidrug loading and programmable release of each drug, which are very important to achieve synergistic effects in tissue engineering and disease therapy. The advantages offered by these materials encourage us to further understand the relationship between colloidal properties and fibers, to predict the morphology and properties of the fibers obtained by colloid-electrospinning, and to explore new possible combination of properties offered by nanoparticles and nanofibers.