Self-healing polyvinyl chloride (PVC) based on microencapsulated nucleophilic thiol-click chemistry

Self-Healing Polymers and Composites: Extrinsic Routes

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Polymers have the property to convert the physical stress to covalent bond shuffling, thereby acting as the healing agents. Polymeric coatings, paints, electronic devices, drug delivery, and many other applications find self-healing materials as a smart technique to prolong the life cycle of the end products. The idea behind these artificial materials is to make them behave like the human body. It should sense the failure and repair it before it becomes worse or irreparable. Researchers have explored several polymeric materials which can self-heal through intrinsic or extrinsic mechanisms. This review specifically focuses on extrinsic routes governed by mechanical stress, temperature change in a covalent bond, humidity, variation in pH, optical sensitivity, and electrochemical effects. Each possible mechanism is further supported by the molecules or bonds which can undergo the transformations under given conditions. On a broader scale, bonds that can self-repair by mechanical force, thermal treatment, chemical modifications, UV irradiation, or electromagnetic phenomenon are covered under this review. It brings into the notice the shortcomings or challenges in adopting the technology to the commercial scale. The possible molecules or bonds which can undergo self-healing under certain conditions have been distinctly presented in a well-segregated manner. This review is envisaged to act as a guide for researchers working in this area.

High-Strength, Fast Self-Healing, Aging-Insensitive Elastomers with Shape Memory Effect

Self-healing materials, which can autonomously repair damages like living organisms, have undergone extensive development in the last decades. The bottleneck problems for their practical applications are long healing time, inferior mechanical strength, and aging sensitivity. Here, a new class of polymeric materials rationally grafted with oligo poly(ethylene glycol) is reported. The network based on the formation of multiple weak hydrogen bonds endows the elastomers with good comprehensive performances including high stretchability (725%), high strength (4.20 MPa), and fast self-healing process (40 s). Benefiting from characteristic multiple weak hydrogen bond interactions, the fractured elastomers maintain high healing efficiency even after aging for 192 h, showing an unusual aging insensitivity. A Sudoku structural device based on the developed elastomer shows shape memory effect, providing a new avenue for fabricating novel smart devices with complicated shapes.

Repeatedly Intrinsic Self-Healing of Millimeter-Scale Wounds in Polymer through Rapid Volume Expansion Aided Host-Guest Interaction

Implantable and wearable materials, which are usually used in/on a biological body, are mostly needed with biomimetic self-healing function. To enable repeatable large-wound self-healing and volume/structure recovery, we verified a proof-of-concept approach in this work. We design a polymer hydrogel that combines temperature responsiveness with an intrinsic self-healing ability through host-guest orthogonal self-assembly between two types of poly(N-isopropylacrylamide) (PNIPAM) oligomers. The result is thermosensitive, capable of fast self-repair of microcracks based on reversible host-guest assembly. More importantly, when a large open wound appears, the hydrogel can first close the wound via volume swelling and then completely self-repair the damage in terms of intrinsic self-healing. Meanwhile, its original volume can be easily recovered by subsequent contraction. As demonstrated by the experimental data, such millimeter-level wound self-healing and volume recovery can be repeatedly carried out in response to the short-term cooling stimulus. With low cytotoxicity and good biocompatibility, moreover, this highly intelligent hydrogel is greatly promising for practical large-wound self-healing in wound dressing, electronic skins, wearable biosensors, and humanoid robotics, which can tolerate large-scale human motions.

Light-Healable Epoxy Polymer Networks via Anthracene Dimer Scission of Diamine Crosslinker

Two anthracene-based diamine crosslinkers were used to cure a range of commercially available monomers to produce four highly photoreversible crosslinked epoxy polymers. Through careful selection of the epoxy monomers used, the properties of the resultant polymer networks were varied to create a coating material that possessed room-temperature light-stimulated healing. Of the four coatings created, the best healing performance was exhibited by the two most flexible systems, both of these also exhibited the thermal and mechanical performance necessary for coatings. By using anthracene, the utilization of a wide range of wavelengths in the healing process is possible, which in applications such as industrial coatings would be of significant benefit.

Self-Healing of Polarizing Films via the Synergy between Gold Nanorods and Vitrimer

Conventional self-healing is about the recovery of shape and mechanical properties. In contrast, recovery of functional properties is still a great challenge, especially for optical functional materials, as the known self-healing methods are incompatible with optical properties. By utilizing the synergistic effect between Au nanorods and vitrimer, the alignment of Au nanorods can be achieved in the crosslinked polymer. The optical properties of the resulting polarizing film, such as light transmittance and polarization degree, can be fully recovered without an external repair agent. With simple laser irradiation to induce the photothermal effect of Au nanorods, the shape-memory effect of vitrimer returns the Au nanorods to their initial orientation, and the plasticity achieves in situ self-healing of the cutting area. The self-healing of polarizing film provides a new research direction and reference for the application of self-healing systems in functional materials.

Improvement and tuning of the performance of light-healable polymers by variation of the monomer content

High-performing crosslinked epoxy coatings that possess room temperature self-healing ability by the use of a newly synthesised dynamic diamine crosslinker.

Improving Kinetics of "Click-Crosslinking" for Self-Healing Nanocomposites by Graphene-Supported Cu-Nanoparticles

Investigation of the curing kinetics of crosslinking reactions and the development of optimized catalyst systems is of importance for the preparation of self-healing nanocomposites, able to significantly extend their service lifetimes. Here we study different modified low molecular weight multivalent azides for a capsule-based self-healing approach, where self-healing is mediated by graphene-supported copper-nanoparticles, able to trigger "click"-based crosslinking of trivalent azides and alkynes. When monitoring the reaction kinetics of the curing reaction via reactive dynamic scanning calorimetry (DSC), it was found that the "click-crosslinking" reactivity decreased with increasing chain length of the according azide. Additionally, we could show a remarkable "click" reactivity already at 0 °C, highlighting the potential of click-based self-healing approaches. Furthermore, we varied the reaction temperature during the preparation of our tailor-made graphene-based copper(I) catalyst to further optimize its catalytic activity. With the most active catalyst prepared at 700 °C and the optimized set-up of reactants on hand, we prepared capsule-based self-healing epoxy nanocomposites.

Self-healing of thermally molded commodity plastics based on heat-resistant and anti-aging healing systems

Thermally molded commodity plastics become self-healable by the incorporation of heat-resistant and anti-aging healants.

Self-healing epoxy with a fast and stable extrinsic healing system based on BF3–amine complex

An easily processed healing system consisting of BF₃–amine complex and cycloaliphatic epoxy monomer enables fast healing of cured epoxy within seconds.