Enhanced Dissipation Behavior of Main-Chain LCE Networks

Liquid Crystal Elastomers (LCEs) are composed of mesogens bound to an elastomeric network of polymer chains. The orientation mesogens relative to the polymer network leads to reversible actuation at the nematic-isotropic transition (Tni), soft-elasticity, and enhanced dissipation. Instead of a peak at Tg, the tan-delta curve for LCEs is elevated over Tg-Tni, indicating enhanced dissipation. At large strains, the material exhibits rate-dependent soft-elasticity with hysteresis[1]. We hypothesize that the enhanced dissipation behavior arises from the motion of the mesogens relative to the polymer network and measure the effect of mesogen ordering and network orientation. We developed uniaxial tension tests using 3D-DIC to measure the rate-dependent load-unload response and hysteresis for 3 main chain LCE networks with different microstructures, including polydomain and monodomains. The modulus and hysteresis increased significantly with strain rate for all networks. The modulus for a monodomain stretched parallel to the director was an order of magnitude higher than that of a polydomain. The monodomain stretched perpendicular to the director had the greatest dissipation.
[1] A. Azoug, V. Vasconcellos, J. Dooling, M. Saed, C. M. Yakacki and T. D. Nguyen (2016), Polymer: 98, 165-171.