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Self-repairing materials are of great interest in the automotive and electronics industries because of their ability to restore damaged parts in response to irritation. Coated surfaces with self-healing polymers easily remove scratches and provide corrosion protection to the substrate. In addition, these polymers have applications in manufacturing (e.g., 3D printing of cross-linked networks), recycling, or repair; such materials extend the life of equipment by repairing fatigue and cracks.
There are many ways to trigger self-repair, including heat, light, pH, humidity and electromagnetic fields. For example, heat can induce dynamic covalent bond exchanges such as the Diels-Alder (DA) reaction, disulfide exchange, or ester exchange. Thermally reversible bonding of dienes (furans) and pro-dienes (maleimides) is utilized to induce DA and reverse DA (rDA) reactions. At high temperatures (100-120°C), rDA reactions occur, leading to bond breakage. Upon cooling, the DA bonds are reorganized. Using this phenomenon, the chemical bonds in the cracked sample can first be rearranged at high temperatures (rDA reaction), allowing the material to return to its initial shape upon cooling (DA reaction).
Nanomaterials have been incorporated into polymers to trigger internal electromagnetic heating to prepare nanocomposites with healing capabilities.Li et al. utilized carbon nanotubes (CNTs)/ da - epoxy resin, irradiated with near-infrared radiation (NIR) induced heat, to trigger rDA.Cai et al. used graphene in epoxy composites and triggered healing by multiple methods (microwave/IR irradiation) Son et al. Man used a photothermal dye in dynamically hindered urea to create a transparent composite that was applied to the exterior surfaces of automobiles and used sunlight to trigger self-healing of these parts Wang et al. combined epoxy polycaprolactone (PCL) with titanium nitride nanoparticles for self-repairing corrosion protection using photothermal heating. When irradiated with near-infrared light, the shape memory of PCL seals scratches and restores barrier properties, effectively stopping corrosion in the damaged area To date, most research has been conducted on surface-coated materials, focusing mainly on self-healing of adhesives and equipment.
The main point of this paper
Embedded healing and reversible adhesion applications:
It can be used for joints, device materials (e.g., circuits, dielectric layers, and substrates).
Mojtabai et al. synthesized a reversible epoxy adhesive that can be peeled off on demand under light irradiation.
Wang et al. prepared shape memory self-soldering tapes containing AgNP for interconnection during circuit healing.
Launay et al. used NIR organic dyes for scratch healing and thermoplastic bonding/debonding under light irradiation.
Advantages of radio frequency (RF) heating:
Does not require direct exposure to a light source, penetrates most polymeric substances, and heats only the carbon receptors.
Non-contact RF fields can penetrate samples several millimeters deep, facilitating precise heating in small spaces.
RF induction heating applications:
Used to selectively heat and cure RF receptor-containing thermoset adhesives, bonding plastics without distorting surrounding components.
RF heating is assumed to enable self-healing and reversible bonding with the advantages of non-contact and directional heating.
Dynamic covalent polymer networks and Diels-Alder polymers (DAP):
Sukhishvili et al. used DAP to prepare materials with high stiffness tunability and fast self-healing behavior.
The solid-liquid reversible dissociation phenomenon of DAP was used to 3D print structures with shape memory behavior.
Joule heating was applied to DAP/CNT composites to trigger self-healing and shape memory effects.
Joule heating behavior in RF fields:
The Joule heating behavior of DAP in RF fields and its role in embedment healing and reversible adhesion were investigated.
Targeted and selective RF heating was successfully used to induce healing responses in scratched DAP samples between polymer layers.
In samples embedded in polydimethylsiloxane (PDMS), fractures could be healed using RF heating methods.
A new application of RF-induced Joule heating:
New applications of RF-induced Joule heating in the field of healable polymers are provided.
By adding a very low carbon receptor loading (0.5 wt%) to the DAP, RF heating was used to promote reversible bonding in polymers
Radiofrequency (RF) Joule heating triggers dynamic covalent bond exchange:
It has been shown that by adding carbon nanotubes (CNTs) to furan-maleimide Diels-Alder polymers (DAPs), it is possible to make the materials responsive to radiofrequency (RF) fields and to achieve selective, non-contact restorative behavior of the DAPs after exposure to an electric field.
Mechanical test results:
Mechanical tests performed after healing showed that the healed samples recovered 96.2% of their tensile strength and 83.2% of their toughness, compared to the mechanical properties of the original undamaged samples
Reversible Adhesion and Repeated Bonding/Debonding:
RF heating of the DAP/CNT allows for repeated bonding and debonding of the material, resulting in on-demand bonding and debonding
In conclusion, our study demonstrates the Joule heating behavior of DAP/CNT composites in RF fields and the selective targeted healing of DAP/CNT when embedded in polymers. Embedded repair by RF heating allows the repair of damaged parts encased in polymer coverings without disassembling or removing the polymer shell. In experiments simulating embedding scenarios, damaged DAP/CNT composites were wrapped in PDMS and subjected to RF fields. The result was a successful healing process occurring in the specified target area. Evaluating the mechanical properties before and after RF healing, tensile tests showed a tensile strength recovery of more than 90%.
In addition, the on-demand bonding and debonding kinetics of DAP under RF heating were investigated. DAP samples bonded using RF heating showed lap shear strengths ranging from 0.38 to 0.68 MPa over three bonding cycles, with debonding occurring less than 20 seconds after RF field activation and less than 5 seconds after reaching 100°C. This comprehensive study not only emphasizes the efficacy of RF-induced healing, but also demonstrates the multifunctional potential of controlled bonding and debonding.
