Highly Stretchable and Self-Healable Tough Polymer Elastomer through Dy³⁺ and Cu²⁺ Coordination Cross-Linking

Abstract

Herein we report a carboxylated nitrile butadiene rubber (XNBR) elastomer design that merges high stretchability, toughness, and self-healing through Cu 2+ -COOH-TEA and Dy 3+ -COOH-TEA coordination (TEA denotes triethylamine). The TEA molecules as extra ligands stiffen the coordination complexes. The Cu 2+ -COOH-TEA coordination leads to the formation of fast relaxation cross-links, mainly contributing to energy dissipation. In contrast, the Dy 3+ -COOH-TEA coordination results in the generation of slow relaxation cross-links, mainly contributing to the mechanical strength. The theoretical simulations demonstrate the multiple breaking/reformation modes of the coordination cross-links during stretching, where Dy 3+ -mediated cross-links decrease but become more robust, while Cu 2+ -mediated cross-links break rapidly but can be almost fully recovered in the form of more dynamic cross-links. Finally, the XNBR/TEA/Cu/Dy elastomer achieves high stretchability (∼5000%), high strength (6.6 MPa), and temperature-adaptable self-healing. The coexistence of Cu 2+ and Dy 3+ coordination complexes also improves the self-healing efficiency of the XNBR/TEA/Cu/Dy elastomer. We also demonstrate that this elastomer can be used to integrate with the liquid metal for fabricating the stretchable and healable soft conductor. Our work paves a new pathway for fabricating self-healable soft electronics and wearable devices, where high mechanical strength, high stretchability, and temperature-adaptable self-healing can be concurrently achieved.

Microscopic Mechanisms of Self-Healing in Polymers Revealed by Molecular Simulations and Machine Learning

“…The self-healing efficiencies of the healed systems increase gradually with the increase of the healing time and then level off. That is, the increase in the healing time can lead to the improvement in the self-healing efficiencies of the systems, which is consistent with the experimental results. ,,,− ,, It should be noted that in Figure b, the self-healing efficiency of the healed system with a healing time of 5700τ is 85.76%, while the normalized content of beads/chain centroids/reversible interaction pairs at the end of the healing process is only around 0.3. This simulated self-healing efficiency appears to be higher.…”

“…There are a variety of methods for preparing self-healing polymers, among which the construction of reversible bonds or interactions in polymers is one of the most relevant. − For instance, hydrogen bonds, ,,− reversible covalent bonds, ,, metal–ligand coordination, − and ionic interactions , are introduced into polymers to achieve the self-healing ability. Among them, hydrogen-bonded self-healing polymers have attracted much attention due to the simple preparation process and the ease of industrial production. , …”

“…In short, the microscopic mechanism of the self-healing in polymers should be revealed, which is the prerequisite for preparing self-healing polymers with high mechanical properties and high self-healing efficiency. ,,, Computer molecular simulation is an effective tool to study the microstructure changes of polymer materials. ,− Currently, molecular simulation provides a new way to investigate the microscopic mechanism of the self-healing in polymers. ,− For instance, Liu et al performed molecular dynamic (MD) simulations to study the self-healing behaviors of topological copolymers with a comblike structure . Luo et al focused on the self-healing mechanism of a polyurethane-urea elastomer based on hydrogen bonds .…”