Influence of Network Structure on Fracture Toughness of Nematic Elastomers

Liquid crystal elastomers (LCEs) exhibit unusual viscoelastic behaviors like an elevated damping ratio over wide temperature and frequency ranges and large rate-dependent hysteresis. Recent studies demonstrated that the enhanced dissipation contributes to the toughness of LCE sheets. These studies examined effects of loading rate and degree of alignment by comparing polydomain, monodomain, and isotropic phases, but only for one LCE formulation. We aim to investigate the effect of network structure on rate-dependent toughening mechanisms. We synthesized mono- and polydomain LCEs with Young’s modulus from 2 to 31 MPa by varying the fraction of thiol crosslinker and excess acrylate, which has been shown to affect the damping ratio and rate-dependent stress response. In monodomain LCEs, polarized light imaging revealed a greater degree of mesogen rotation in more lightly crosslinked samples for the same applied strain. We will conduct pure shear fracture tests on different LCE formulations in tandem with stereoscopic digital image correlation and polarized light imaging to understand the interplay between the underlying mechanisms contributing to the fracture toughness including network elasticity, chain mobility, and mesogen rotation.