Self-healing Materials Research Articles

'Donor-acceptor', 'interpenetrating polymer network' and 'electrostatic self-assembly' work in tandem to achieve extraordinary specific shielding effectiveness.

The exploration of 'electrostatic self-assembly' on solid surfaces has garnered significant interest across various fields. With the sophistication of gadgets, managing electromagnetic interference (EMI) from stray signals, especially in stealth applications, necessitates materials that can absorb microwaves. A promising approach involves integrating lightweight self-healing polymeric materials. This study employs electrostatic self-assembly to design a carbon nanotube structure on an interpenetrating polymer network (IPN) made of PVDF and bismaleimide (BMI)-grafted dopamine hydrochloride, enhancing mechanical integrity through well-formed IPNs. Graphene oxide (GO) is introduced before IPN formation to facilitate an 'acceptor-donor' interaction via the Diels-Alder adduct between BMI and GO, which binds with multi-walled carbon nanotubes (MWCNTs). MWCNTs, modified with PQ7 or PDDA for a positive charge, self-assemble onto the IPN-GO construct, creating a lightweight and chemically stable structure capable of absorbing electromagnetic radiation. The 21 μm thick construct exhibits enhanced microwave absorption within the X-band (8.2-12.4 GHz), with a specific shielding effectiveness of 8637 dB cm2 g-1 and a green index (gs ≈ 1.41). The construct is coated with self-healable polyetherimide (PEI) containing exchangeable disulfide bonds to address maintenance challenges, providing heat-triggered self-healing properties. These innovative structures offer solutions for 5G and IoT applications where lightweight, durable, and multifunctional properties are essential for effectively shielding electronic devices from stray signals.

Retraction: Interfacial adsorption study of nitrogen based inhibitors in silane nanocontainers as anticorrosive and self-healing material for steel in strong acid solution

Retraction of ‘Interfacial adsorption study of nitrogen based inhibitors in silane nanocontainers as anticorrosive and self-healing material for steel in strong acid solution’ by Darris M. S. et al., J. Mater. Chem. A, 2023, Accepted Manuscript, https://doi.org/10.1039/D3TA02203J.

Expression of concern: Interfacial adsorption study of nitrogen based inhibitors in silane nanocontainers as anticorrosive and self-healing material for steel in strong acid solution

Expression of concern for ‘Interfacial adsorption study of nitrogen based inhibitors in silane nanocontainers as anticorrosive and self-healing material for steel in strong acid solution’ by Darris M. S. et al., J. Mater. Chem. A, 2023, https://doi.org/10.1039/d3ta02203j.

Structural design underpinning self-healing materials for electromagnetic interference shielding: coupling of dynamic polymer chemistry and electrical conductivity

Electromagnetic interference shielding materials can address the troublesome problem of electromagnetic pollution, but they are inevitably subject to damage during use, severely weakening or depriving them of their inherent shielding performance.

Toward mechanically robust self-healing polyurethanes using dynamics chemistry

Recent advances in the design strategy, healing mechanism, and potential applications of mechanically robust self-healing PU elastomers.

FRACTAL SURFACE RECOVERY AND SELF-HEALING CONTRIBUTED TO SUSTAINABLE SUPERHYDROPHOBICITY: A REVIEW

The concept of superhydrophobicity has been widely used after years of theoretical and experimental exploration. Researchers have obtained materials with excellent surface superhydrophobicity for numerous areas (e.g. textiles, paints, and coatings industries), through different design and synthesis methods using low surface energy components (LSECs) and micro/nanohierarchy composite structures. However, the durability of superhydrophobic material surfaces has gradually become a prominent obstacle to restricting applications. In this paper, advances in improving the durability of superhydrophobic surfaces in the past decade are reviewed, covering different schemes for recovering fractal surfaces based on the LSECs and micro/nanocomposite structures. It also presents a balanced review on wet chemical methods, chemical vapor deposition (CVD), layer-by-layer (LbL), microarc oxidation (MAO), and self-healing of the fractal surfaces, with the aim at developing sustainable superhydrophobicity. In addition, it innovatively summarized the research on the synthesis of self-healing superhydrophobic materials by machine learning methods. By the end it discusses perspectives on future development in this emerging research area.

A Sol-Gel Transition and Self-Healing Hydrogel Triggered via Photodimerization of Coumarin.

Reversible chemical covalency provides a path to materials that can degrade and recombine with appropriate stimuli and which can be used for tissue regeneration and repair. However, designing and preparing efficient and quickly self-healing materials has always been a challenge. The preparation strategies of photoresponsive gels attract a lot of attention due to their precise spatial and temporal control and their predetermined response to light stimulation. In this work, the linear copolymer PAC was synthesized via precipitation polymerization of acrylic acid and 7-(2-acrylate-ethoxylated)-4-methylcoumarin. The coumarin groups on the copolymer PAC side chains provide a reversible chemical cross-linking via photostimulation, which achieves reversible regulation of the gel network structure. The concentration of 18 wt% PAC solution produces gelation under irradiation with 365 nm. In contrast, PAC gel is restored to soluble copolymers under irradiation with 254 nm. Meanwhile, the mechanical and self-healing properties of the gel were also explored. It is demonstrated that the cracks of the gel can be repaired simply, quickly, and efficiently. Furthermore, the PAC copolymer shows an excellent adhesion property based on the reversible sol-gel transition. Thus, the PAC gel has considerable potential for applications in engineering and biomedical materials.

Functional Zwitterionic Polyurethanes: State-of-the-Art Review.

Recent advancements in bioengineering and medical devices have been greatly influenced and dominated by synthetic polymers, particularly polyurethanes (PUs). PUs offer customizable mechanical properties and long-term stability, but their inherent hydrophobic nature poses challenges in practically biological application processes, such as interface high friction, strong protein adsorption, and thrombosis. To address these issues, surface modifications of PUs for generating functionally hydrophilic layers have received widespread attention, but the durability of generated surface functionality is poor due to irreversible mechanical wear or biodegradation. As a result, numerous researchers have investigated bulk modification techniques to incorporate zwitterionic polymers or groups onto the main or side chains of PUs, thereby improving their hydrophilicity and biocompatibility. This comprehensive review presents an extensive overview of notable zwitterionic PUs (ZPUs), including those based on phosphorylcholine, sulfobetaine, and carboxybetaine. The review explores their wide range of biomedical applications, from blood-contacting devices to antibacterial coatings, fouling-resistant marine coatings, separation membranes, lubricated surfaces, and shape memory and self-healing materials. Lastly, the review summarizes the challenges and future prospects of ZPUs in biological applications.

Mechanical properties, durability and self-healing performance of mortar containing double-layers capsules

To improve the self-healing performance of cementitious materials and minimize the negative impact of self-healing materials on mortar, a novel type of double-layer capsules is developed in this study. The developed double-layer capsule includes the rapid hardening cement as the internal wall and polyvinyl alcohol (PVA) as the external wall. To evaluate its impact on mortar, two factors (i.e., capsule size and dosage) are considered and the correspondent experiments of investigating mechanical properties, durability, and self-healing performance are conducted. Experimental results present that the double-layer capsules reduce the flexural and compressive strength of mortar. With a reduced capsule size and a small ratio of the dosage, the negative impact the capsule gradually weakens. Moreover, the mixing of capsules slightly decreases the chloride penetration resistance and carbonation resistance of mortar specimens, while improves the frost resistance and impermeability greatly when the dosage is within 10%. Furthermore, the capsules can significantly improve the self-healing capacity of mortar. Especially when the capsule size is 2.36–3.2 mm and the dosage is 10%, the healing effect on matrix is highest. In addition, the XRD\\SEM\\XCT results indicated that the healing products mainly include C-S-H gel, CaCO3, Aft and Mg-containing compounds, the filling and bonding effects of which realize the automatic and effective recovery of matrix properties.

Anti-Entropy Aggregation of Minority Groups in Polymers: Design and Applications.

Minority groups are non-repeating units with very low content that inevitably exist in polymers. Typically, these minority groups are easily surrounded by the majority of repeating units and randomly dispersed, maximizing the entropy of minority groups. In the concept, anti-entropy aggregation (AEA) of minority groups is described, and different pathways are outlined. They are polymer crystallization-driven AEA, supramolecular interaction-induced AEA, phase separation-confined AEA, and hierarchical interactions-driven AEA. Typical applications of AEA materials are also presented, including fluorescence probes, self-healing materials, ion transporting regulation, and osmotic energy conversion. The concept of AEA is expected to inspire the fabrication of novel functional systems.

Rapid self-assembly of self-healable and transferable liquid metal epidermis

Healable electronic skins, an essential component for future soft robotics, implantable bioelectronics, and smart wearable systems, necessitate self-healable and pliable materials that exhibit functionality at intricate interfaces. Although a plethora of self-healable materials have been developed, the fabrication of highly conformal biocompatible functional materials on complex biological surfaces remains a formidable challenge. Inspired by regenerative properties of skin, we present the self-assembled transfer-printable liquid metal epidermis (SALME), which possesses autonomous self-healing capabilities at the oil–water interface. SALME comprises a layer of surfactant-grafted liquid metal nanodroplets that spontaneously assemble at the oil–water interface within a few seconds. This unique self-assembly property facilitates rapid restoration (<10 s) of SALME following mechanical damage. In addition to its self-healing ability, SALME exhibits excellent shear resistance and can be seamlessly transferred to arbitrary hydrophilic/hydrophobic curved surfaces. The transferred SALME effectively preserves submicron-scale surface textures on biological substrates, thus displaying tremendous potential for future epidermal bioelectronics.

Self-healing polyurethane elastomer with ultra-high mechanical strength and enhanced thermal mechanical properties

Polyurethane (PU) materials are widely used due to their excellent comprehensive properties including high strength, good wear resistance and weather resistance. To further improve the service life and safety of polyurethane materials, self-healing polyurethane materials have been developed. However, self-healing polyurethane generally suffers from low mechanical strength and poor thermal mechanical properties. Here, we have constructed a strong dual network by introducing benzene-1,4-diboronic acid (PDBA) into poly(urethane-urea) (PUU). On one hand, PDBA can form coordination bonds with nitrogen atoms in PUU, leading to the formation of a dual network consisting of boron-nitrogen coordination and hydrogen bonding. This dual network imparts PUU with a maximum tensile strength of 84.2 MPa. On the other hand, boron-nitrogen coordination is more stable than hydrogen bonding at high temperature, thereby significantly enhancing the thermal mechanical properties of PUU (the mechanical strength of PUU-PDBA-50 % and PUU-PDBA-100 % increased by 1.8 times and 2.4 times, respectively, compared to PUU at 100 °C). Meanwhile, the dynamic nature of the dual network endows the material with self-healing ability.

Self-Healing Polymers Designed for Underwater Applications

Polymeric materials have been employed in a wide range of applications in both dry and wet environments. When these materials suffer damage, it becomes crucial to initiate repairs in order to mitigate further losses. The use of self-healing materials emerges as a promising strategy not only to address this issue but also possess the advantage of prolonging the product’s lifespan. Nevertheless, the development of self-healing materials tailored for wet environments presents a set of obstacles and complexities. The review examines the current state of research in the field and highlights the challenges associated with developing self-healing materials that can effectively repair damage in such environments. We discuss the self-healing mechanisms and various polymers that are extensively employed in the advancement of self-healing materials. We study the progress made in the research and development of self-healing materials specifically designed for wet environments. Furthermore, it provides a summary of various applications of self-healing materials in wet environments.

3D Printing of Self-Healing Materials.

This review article presents a comprehensive overview of the latest advances in the field of 3D printable structures with self-healing properties. Three-dimensional printing (3DP) is a versatile technology that enables the rapid manufacturing of complex geometric structures with precision and functionality not previously attainable. However, the application of 3DP technology is still limited by the availability of materials with customizable properties specifically designed for additive manufacturing. The addition of self-healing properties within 3D printed objects is of high interest as it can improve the performance and lifespan of structural components, and even enable the mimicking of living tissues for biomedical applications, such as organs printing. The review will discuss and analyze the most relevant results reported in recent years in the development of self-healing polymeric materials that can be processed via 3D printing. After introducing the chemical and physical self-healing mechanism that can be exploited, the literature review here reported will focus in particular on printability and repairing performances. At last, actual perspective and possible development field will be critically discussed.

Self-healing recyclable polymers based on azobenzenes with thermoset like behaviour

Self-healing materials are considered intelligent materials capable of recovering their original shapes from damaged or distorted forms after exposure to specific stimuli, such as chemicals, heat, moisture, or light. The utilization of thermoreversible crosslinks in polymer networks has garnered increasing interest as a method to create such materials. In these polymers, damage can be repaired simply by heating them above a gel-liquid transition temperature. Upon cooling, the material regains its previous cross-linked properties. However, finding alternative external stimuli other than heat presents an intriguing challenge. Among the various possibilities, light is the preferred choice due to its potential for remote and spatially-controlled activation. Additionally, the process can be easily paused and resumed by turning the excitation light on and off.Furthermore, the photo-switching of the glass transition temperature (Tg) in azobenzene-containing polymers induces reversible transitions from a solid to a liquid state. These reversible trans-to-cis transitions are triggered by UV and visible light irradiation. This phenomenon offers a novel approach to designing healable polymers and allows for precise control over the mechanical properties of polymers with spatio-temporal resolution.The main objective of this study is to investigate the feasibility of using light as a self-healing trigger in a recyclable polymer based on physically cross-linked epoxy/amine formulations. To achieve this goal, the matrix was modified with 4-phenylazophenol (PAP), which forms homogeneous blends with the polymer through hydrogen bond interactions. Films were prepared and characterized using various experimental techniques. Polymerization kinetics of samples with and without PAP was determined using FTIR, which was also employed for characterizing the final materials. Tg of the resulting products was measured using DSC, revealing a decrease in its value for PAP-modified samples. The transition from a solid to a liquid state during UV light irradiation was observed using rheometric analysis. The reversible photoisomerization behaviour of epoxy/amine/PAP was investigated using UV–visible spectroscopy in films prepared by spin-coating THF solutions.The ability of the material to self-heal at room temperature using light as a remote source was confirmed through TOM (Transmission Optical Microscopy) observations and quantified by profilometric measurements. In addition, surface mechanical properties were evaluated in order to determine the effect of the incorporation of the PAP, and the ability of the repaired material to recover its properties. Promising findings indicate that this recyclable polymer holds significant potential for multiple applications where its self-healing ability will be of great importance.

A Room-Temperature Self-Healing Liquid Metal-Infilled Microcapsule Driven by Coaxial Flow Focusing for High-Performance Lithium-Ion Battery Anode.

Liquid metals have attracted a lot of attention as self-healing materials in many fields. However, their applications in secondary batteries are challenged by electrode failure and side reactions due to the drastic volume changes during the "liquid-solid-liquid" transition. Herein, a simple encapsulated, mass-producible method is developed to prepare room-temperature liquid metal-infilled microcapsules (LMMs) with highly conductive carbon shells as anodes for lithium-ion batteries. Due to the reasonably designed voids in the microcapsule, the liquid metal particles (LMPs) can expand freely without damaging the electrode structure. The LMMs-based anodes exhibit superior capacity of rete-performance and ultra-long cycling stability remaining 413mAhg-1 after 5000 cycles at 5.0Ag-1. Ex situ X-ray powder diffraction (XRD) patterns and electrochemical impedance spectroscopy (EIS) reveal that the LMMs anode displays a stable alloying/de-alloying mechanism. DFT calculations validate the electronic structure and stability of the room-temperature LMMs system. These findings will bring some new opportunities to develop high-performance battery systems.

High performance photodegradation resistant PVA@TiO2/carboxyl-PES self-healing reactive ultrafiltration membrane

The occurrence of ultrafiltration (UF) membrane fouling frequently hampers the sustainable advancement of UF technology. Reactive self-cleaning UF membranes can effectively alleviate the problem of membrane fouling. Nevertheless, the self-cleaning process may accelerate membrane aging. Addressing these concerns, we present an innovative design concept for composite self-healing materials based on self-cleaning UF membranes. To begin, TiO2 nanoparticles were incorporated into the polymer molecular structure via molecular design, resulting in the synthesis of TiO2/carboxyl-polyether sulfone (PES) hybrid materials. Subsequently, the nonsolvent-induced phase inversion technique was employed to prepare a novel of UF membrane. Lastly, a polyvinyl alcohol (PVA) hydrogel coating was applied to the hybrid UF membrane surface to create PVA@TiO2/carboxyl-PES self-healing reactive UF membranes. By establishing a covalent bond, the TiO2 nanoparticles were effectively and uniformly dispersed within the UF membrane, leading to exceptional self-cleaning properties. Furthermore, the water-absorbing and swelling properties of PVA hydrogel, along with its capacity to form hydrogen bonds with water molecules, resulted in UF membranes with improved hydrophilicity and active self-healing abilities. The results demonstrated that the water contact angle of PVA@5%TiO2/carboxyl-PES UF membrane was 43.1°. Following a 1-h exposure to simulated solar exposure, the water flux recovery ratio increased from 48.16% to 81.03%. Moreover, even after undergoing five cycles of 12-h simulated sunlight exposure, the UF membranes exhibited a consistent retention rate of over 97%, thus fully demonstrating their exceptional self-cleaning, antifouling, and self-healing capabilities. We anticipate that the self-healing reactive UF membrane system will serve as a pioneering and comprehensive solution for the self-cleaning antifouling challenges encountered in UF membranes while also effectively mitigating the aging effects of reactive UF membranes.

Highly Self-Healable Polymeric Coating Materials Based on Charge Transfer Complex Interactions with Outstanding Weatherability.

In this study, we prepare highly self-healable polymeric coating materials using charge transfer complex (CTC) interactions. The resulting coating materials demonstrate outstanding thermal stability (1 wt% loss thermal decomposition temperature at 420 °C), rapid self-healing kinetics (in 5 min), and high self-healing efficiency (over 99%), which is facilitated by CTC-induced multiple interactions between the polymeric chains. In addition, these materials exhibit excellent optical properties, including transmittance over 91% and yellow index (YI) below 2, and show enhanced weatherability with a ΔYI value below 0.5 after exposure to UV light for 72 h. Furthermore, the self-healable coating materials developed in this study show outstanding mechanical properties by overcoming the limitations of conventional self-healing materials.

Highly entangled elastomer with ultra-fast self-healing capability and high mechanical strength

Self-healing polymeric material, which can heal the cracks repeatedly and thus definitely prolong their lifetime in practical applications, has attracted intensive interesting in recent years. However, it is still a great challenge to both achieve fast self-healing ability and high mechanical strength. Considering the mechanism of fast self-healing is the re-bonding of dynamic bonds in the fracture surfaces, the dense physical cross-linking might be a good option for fast self-healing polymer to solve the trade-off between self-healing ability and mechanical strength. To this end, the highly entangled polymer chains are thereby introduced to improve the mechanical strength of the elastomer by simply increasing the monomer concentration. As expected, the mechanical strength of the resultant elastomers increases with monomer concentration, accompanied by a slight decline in self-healing ability. In addition, further increment of the mechanical strength to 18.4 Mpa is achieved by introducing anisotropic structure into the highly entangled polymers by pre-stretching. Most importantly, the resultant polymer exhibits high recovery and fast self-healing ability with a healing efficiency of 86.2 % after only 30 s healing at room temperature. Moreover, the highly entangled polymer chains also improve the actuation performance of the elastomer with anisotropic structure, which can lift up about 1000 times of its own weight reversibly upon heating–cooling cycles with a maximum tensile stroke of ca. 28 %.

Urea-Functionalized Heterocycles: Structure, Hydrogen Bonding and Applications

Ureido-heterocycles exhibiting different triple- and quadruple H-bonding patterns are useful building blocks in the construction of supramolecular polymers, self-healing materials, stimuli-responsive devices, catalysts and sensors. The heterocyclic group may provide hydrogen bond donor/acceptor sites to supplement those in the urea core, and they can also bind metals and can be modified by pH, redox reactions or irradiation. In the present review, the main structural features of these derivatives are discussed, including the effect of tautomerization and conformational isomerism on self-assembly and complex formation. Some examples of their use as building blocks in different molecular architectures and supramolecular polymers, with special emphasis on biomedical applications, are presented. The role of the heterocyclic functionality in catalytic and sensory applications is also outlined.