Intrinsic Self-Healing Properties of ESOF-Ix Enabled by Diels-Alder Bonds: A Case Study on ESOF-I1.0

The deterioration of adhesive performance often stems from internal cracks. Due to the difficulty of timely detection and repair of micro cracks, the mechanical performance of materials is reduced and their service life is shortened, limiting their application range. Therefore, timely repair of cracks, especially the realization of self-healing of materials, is of great significance for improving the utilization efficiency of materials. The concept of self-healing originates from the healing of biological skin damage, which involves the release and polymerization of repair agents stored inside the material or the reformation of reversible interactions within the material. Self-healing materials can perceive changes in the external environment and respond appropriately, ultimately restoring their own performance. They are a widely applicable and urgently needed type of smart material. Self-healing materials can be divided into two categories. The one is exogenous, which refers to filling the material with composite functional substances to achieve self-healing. Typical repair methods include microcapsule and hollow fiber methods, where the repair mechanism involves adding monomer-containing microcapsules to the material. When the material is damaged, the cracks propagate within the material, and the monomers in the microcapsules are released and come into contact with the catalyst in the material matrix, triggering polymerization and ultimately repairing the damage. However, this type of repair method has obvious limitations, as the repair agents encapsulated in the microcapsules are limited, and once the repair agents are depleted, the material loses its self-healing ability. The other one is intrinsic, which refers to providing energy to the material to enable covalent or non-covalent interactions within the material itself for self-healing. In the absence of external repair agents, reversible interactions are introduced into the polymer matrix, giving it dynamic characteristics and environmental responsiveness, thus achieving self-healing. Compared with exogenous self-healing materials, the biggest advantage of intrinsic self-healing materials is that they can theoretically achieve multiple self-healings. Therefore, ESOF-Ix should have the characteristics of intrinsic self-healing materials due to the incorporation of Diels-Alder bonds. In order to examine the self-healing capability, ESOF-I1.0 was utilized as a representative case and intentionally scratched to create a surface crack. Subsequently, it was subjected to heating at 130℃ for varying durations. As depicted in Figure 5, the crack gradually diminished with increasing heating time, demonstrating exceptional self-healing performance. This phenomenon is due to the fact that Diels-Alder bonds can be disconnected at high temperatures, destroying the cross-linked network structure, increasing the movement ability of the chains, so that the chains can move between the two interfaces of the scratch. After cooling, Diels-Alder bonds can be reformed, but because the relative position of the chains has changed, the structure of the cross-linked network is reconstructed, and the scratch is repaired.