Heterogeneous Local Dynamics in Mussel-Inspired Elastomers

Materialswith increased mechanical strength and toughness bearingmussel-inspired iron-catechol complexes and network architecturesexhibit several dynamic features, e.g., high and broad glass-"transition"temperature, not explored so far. By combining differential scanningcalorimetry and dielectric spectroscopy, the latter as a functionof temperature and pressure, we have explored the increase in theglass temperature, T (g), and the concomitantincrease in the breath of T (g) in bioinspirednetworks bearing one (covalent) or two (covalent and coordination)types of cross-links. Cross-linked networks experience heterogeneous segmental dynamics that are responsible for the broad T (g) range observed in the thermal measurements. The twodistinct dynamics reflect the relaxation of segments in the vicinityversus more distant cross-linked units. The various topologies areshown to have different fragilities and tend to form stronger glasseswith increasing network topology. In addition, the ionic conductivityis influenced by the segmental dynamics and the increased T (g) in the networks. These features (reduced specificheat step, Delta c (p), at T (g) and "strong" dynamic behavior) are alsofound in permanently cross-linked polymers with dynamic network topologyknown as vitrimers. The similarities in the two networksystems are discussed.