[SY-H4] Symposium H-4

[SY-H4] Enhanced Dissipation Behavior of Main-Chain LCE Networks

Invited

^○Thao D Nguyen (Johns Hopkins University, United States of America)

Liquid-crystalline elastomers (LCEs) are soft stimuli-responsive materials that exhibit remarkable mechanical and optical properties. LCEs consist of stiff mesogens, bound in a network of flexible polymer chains, which can self-organize into crystalline order while retaining liquid-like properties. The directional ordering of the mesogens changes in response to external stimuli and the director coupling between the mesogens and network chains brings about unusual behaviors. These include large reversible actuation in response to temperature or light and soft-elasticity. LCEs also exhibit enhanced dissipation behaviors, including a high tan delta 0.5-1.0 for wide range of frequencies and temperatures, spanning the glass and nematic transition temperatures, and large hysteresis in the stress response that increases with the strain rate [1]. We hypothesize that the enhanced dissipation behavior arises from the relative motions of the mesogens within the network and set out to measure the effect of mesogen ordering and network orientation on the enhanced dissipation behavior of LCEs. Experiments were performed to measure the rate-dependent hysteresis and frequency dependent dynamic properties for main-chain LCEs in the nematic state with different network structures, including an unoriented and macroscopically isotropic polydomain as well as monodomains with different degrees of mesogens and chain alignment. Oriented monodomains with an aligned or unaligned network can be synthesized by applying a second-stage crosslinking or exchangeable bond reaction to a stretched LCE sample. In this presentation, I will briefly describe the experimental methods, then compare the dissipative behavior of the different network structures, and discuss how the results will be applied to develop a rate-dependent constitutive model for the main-chain LCE networks.

[1] A. Azoug, V. Vasconcellos, J. Dooling, M. Saed, C. M. Yakacki and T. D. Nguyen (2016) Polymer 98:165-171.