Elastic Characterization of Acrylate-Based Liquid Crystal Elastomers

Liquid crystal elastomers (LCEs) are innovative materials best known for their reversible shape and optical property changes in response to external stimuli such as heat, light, and mechanical forces. These unique features position them as promising candidates for applications in emerging technologies. The determination of the mechanical properties of these materials is important for the study of the interaction between orientational and mechanical deformations of LCEs. Importantly, thoroughly characterizing the mechanical and elastic properties of LCEs is essential for their efficient design and integration into various devices. In this study, a full elastic characterization of promising acrylate-based LCE materials that are auxetic above a material-dependent strain threshold (~0.4 for the material studied here) was carried out. Highly aligned macroscopic samples were fabricated, allowing us to determine, for the first time, the five elasticity coefficients that enter into the elastic-free energy density of acrylate-based LCE materials, as well as the Young's moduli and Poisson ratios. Our approach involves connecting measured strains with elasticity coefficients and using data obtained from three tensile experiments. Specifically, the measured Young's moduli are on the order of MPa, with an anisotropy ratio (E‖/E⟂) of ~4.5. Moreover, the longitudinal Poisson ratios are both close to 0.5, confirming a uniaxial elastic response at low strains in these LCE samples. These findings align with theoretical predictions, indicating a good correspondence between experimental results and established theories.