Heterogeneous Local Dynamics in Mussel-Inspired Elastomers

Abstract

Materials with increased mechanical strength and toughness bearing mussel-inspired iron–catechol complexes and network architectures exhibit several dynamic features, e.g., high and broad glass-“transition” temperature, not explored so far. By combining differential scanning calorimetry and dielectric spectroscopy, the latter as a function of temperature and pressure, we have explored the increase in the glass temperature, Tg, and the concomitant increase in the breath of Tg in bioinspired networks 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 Tg range observed in the thermal measurements. The two distinct dynamics reflect the relaxation of segments in the vicinity versus more distant cross-linked units. The various topologies are shown to have different fragilities and tend to form stronger glasses with increasing network topology. In addition, the ionic conductivity is influenced by the segmental dynamics and the increased Tg in the networks. These features (reduced specific heat step, Δcp, at Tg and “strong” dynamic behavior) are also found in permanently cross-linked polymers with dynamic network topology known as vitrimers. The similarities in the two network systems are discussed.