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

Herein we report a carboxylated nitrile butadiene rubber (XNBR) elastomer design that merges high stretchability, toughness, and self-healing through Cu2+-COOH-TEA and Dy3+-COOH-TEA coordination (TEA denotes triethylamine). The TEA molecules as extra ligands stiffen the coordination complexes. The Cu2+-COOH-TEA coordination leads to the formation of fast relaxation cross-links, mainly contributing to energy dissipation. In contrast, the Dy3+-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 Dy3+-mediated cross-links decrease but become more robust, while Cu2+-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 Cu2+ and Dy3+ 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.