A silicone elastomer with optimized and tunable mechanical strength and self-healing ability based on strong and weak coordination bonds

Abstract

The design and preparation of mechanically strong elastomers accompanied by excellent autonomously self-healable properties is still a huge challenge in the field of self-healing materials, and the introduction of both strong and weak bonds in the same polymer matrix is a feasible method. Herein, we report a dual-crosslinked polydimethylsiloxane (PDMS) polymer network which combines strong and weak metal–ligand interactions through incorporating two potential ligands of Fe³⁺ ions, and the co-existence of strong and weak interactions in this network is verified by spectroscopic analysis and mechanical tests. It was indicated that the weaker Fe/pyridinedicarboxamide (Fe/pdca) coordinations served as sacrificial bonds to efficiently dissipate energy through multiple bonding models such as breaking, exchanging or reforming, while the stronger Fe/N-acetyl-L-cysteine (Fe/NAC) interactions played the role of “permanent” bonds to retain the network integrity and elasticity. Benefiting from the synergistic effect of strong and weak metal–ligand interactions, our elastomer exhibited good mechanical strength as well as autonomous self-healing ability at room temperature. The proportion of weaker Fe/pdca coordinations and stronger Fe/NAC coordinations is also tunable through changing the addition amount of Fe³⁺ ions, resulting in tunable mechanical strength and self-healing ability. Thus, a convenient method to balance the mechanical strength and self-healing ability of elastomers was developed. In addition, it's also found that relatively large amounts of metal ions or a heating process could facilitate the formation of new coordination structures, and further led to stronger mechanical properties. We expect that this strategy of fabricating silicone elastomers by simultaneously incorporating strong and weak metal-coordination bonds into one network could broaden the routes of constructing mechanically strong and autonomously self-healable polymers.