Bond strength regime dictates stress relaxation behavior

Reconfigurable polymer networks are gaining interest for their potential applications as self-healing, recyclable, and stimuli-responsive smart materials. Relating the bond strength of dynamic interactions to material properties including stress relaxation time and modulus is crucial for smart material design. In this work, in situ crosslinked transition metal-terpyridine reconfigurable networks were utilized to modulate the characteristic network stress relaxation time, tau(R). The use of stress relaxation experiments rather than oscillatory frequency sweeps allowed for the measurement of network bond dynamics across a wider dynamic range than has been previously reported. The stress relaxation time was shown to be tunable by metal center, counterion, and crosslink density. Remarkably, the network crosslinked with covalent-like ruthenium chloride-terpyridine interaction, while having a longer tau(R), was qualitatively similar to the other metal-ligand networks. Furthermore, the relaxation time was independent of crosslink density in strongly bonded networks, allowing for independent tunability of modulus and tau(R). In contrast, increasing crosslink density reduced tau(R) in networks crosslinked with weaker interactions.

Automated summary

Reconfigurable polymer networks are smart materials that have the potential applications as self-healing, recyclable, and stimuli-responsive. In this study, transition metal-terpyridine networks were used to modulate the network stress relaxation time, and it was found that the stress relaxation time can be tuned by the metal center, counterion, and crosslink density. It was also observed that networks crosslinked with covalent-like interactions have a longer stress relaxation time but are qualitatively similar to other networks in terms of properties.