The Thermoviscoelastic Behavior of a Main-Chain Liquid Crystal Elastomer

Liquid crystal elastomers (LCEs) combine the anisotropic ordering of liquid crystals and viscoelastic behavior of an elastomeric network. This leads to remarkable mechanical properties, including reversible shape change in response to temperature or light, deformation induced soft elasticity and anisotropy, and extreme dissipation behavior. In this presentation, I will describe our efforts to characterize the rate-dependent and temperature-dependent large deformation behavior of an acrylate main-chain LCE networks to investigate the effects of mesogen order and chain alignment on the stress-strain response, soft elasticity behavior, and hysteresis. The experimental results showed that time-temperature superposition can be applied to the stress response of the LCEs in the nematic state throughout the soft elasticity plateau. All LCE networks, polydomains and monodomains stretched parallel and perpendicular to the director, exhibited the same rate-dependence for the modulus and hysteresis. However, the onset strain and duration of the soft elasticity plateau were relatively insensitive to the strain rate. These findings suggest that the rate-dependent stress response of the acrylate LCEs in the nematic state is insensitive to mesogen reorientation.