In Situ SAXS Observation of Transient Network Behavior in Ionically Cross-Linked Polydimethylsiloxane Elastomer with Slow and Fast Stretching

Abstract

The rupture of noncovalent cross-links with specimen deformation has been frequently regarded as the main cause of the toughness of materials with transient networks. However, the direct observation of the process based on this mechanism is challenging. Through in situ small-angle X-ray scattering, we monitored the transient network behavior with stretching of a polydimethylsiloxane elastomer cross-linked via aggregations of ionic groups attached along the main chain. The results showed that the ionic aggregates elongate along the stretching direction even with minimal strain. Moreover, we first observed the detachment of ionic groups from the ionic aggregates with stretching through the reduction of the aggregate volume. This result demonstrates that the detachment of ionic cross-links is important for toughening this material, where the locally concentrated stress at a given site of the network is dissipated through the detachment of ionic groups from the aggregates, thereby preventing material fracture.