Effects of network structure on the viscoelastic creep and delayed fracture of polyelectrolyte elastomers

Abstract

The past decade has witnessed a significant surge in the field of stretchable ionotronics, wherein stretchable ionic conductors play an essential role. Polyelectrolyte elastomers have been featured as the most promising stretchable ionic conductors for engineering practice owing to their leakage-free nature. However, the inherent viscosity of the ionized polymer networks confounds the responses of the materials thus hampering the applicability of the devices. Therefore, it is of significant importance to study the viscoelastic behaviors and understand the overlayed molecular mechanism. In this work, we study the effects of network structure on the viscoelastic creep and delayed fracture of polyelectrolyte elastomers. We design and synthesize poly(1-[2acryloyloxyethyl]-3-butylimidazolium bis(trifluoromethane) sulfonimide-co-methyl acrylate) elastomer and tune the network structure by changing the covalent crosslink density and the molar ratio between the ionic segment and the neutral segment, which are the two most crucial structural parameters. We perform tensile and creep tests for polyelectrolyte elastomers of different compositions and interpret the creep results, with emphasis placed on the effects of applied stress and strain hardening. In general, the creep deformation is mitigated with increasing covalent crosslink density and the molar ratio between the ionic segment and the neutral segment, suggesting that creep is mainly due to the breakage of ionic bonds and the slippage and movement of polymer chains. This work promotes the understanding of the viscoelastic behaviors of polyelectrolyte elastomers and provides insights for tailoring the mechanical properties through the rational design of polymer networks, which is expected to facilitate the development of next-generation stretchable ionotronic devices.