Liquid crystal elastomers that offer exceptional load-deformation response at low frequencies often require consideration of the mechanical anisotropy only along the two symmetry directions. However, emerging applications operating at high frequencies require all five true elastic constants. Here, we utilize Brillouin light spectroscopy to obtain the engineering moduli and probe the strain dependence of the elasticity anisotropy at gigahertz frequencies. The Young’s modulus anisotropy, E||/E⊥~2.6, is unexpectedly lower than that measured by tensile testing, suggesting disparity between the local mesogenic orientation and the larger scale orientation of the network strands. Unprecedented is the robustness of E||/E⊥ to uniaxial load that it does not comply with continuously transformable director orientation observed in the tensile testing. Likewise, the heat conductivity is directional, κ||/κ⊥~3.0 with κ⊥ = 0.16 Wm−1K−1. Conceptually, this work reveals the different length scales involved in the thermoelastic anisotropy and provides insights for programming liquid crystal elastomers on-demand for high-frequency applications.
【Research Paper】”On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies”
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Published
(School of Materials and Chemical Technology/Dr. Junko Morikawa and Dr. Georgios Fytas)
“On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies”
Nature Communications （DOI: 10.1038/s41467-022-32865-1）
The strain dependence of the elastic anisotropy of liquid crystalline elastomers at gigahertz frequencies was investigated by Brillouin optical spectroscopy. Young’s modulus anisotropy was unexpectedly lower than that measured in tensile tests, suggesting a mismatch between the local mesogenic orientation and the large-scale orientation of the network chains. The strength of Young’s modulus anisotropy to uniaxial load was also unprecedentedly inconsistent with the continuously changing orientation observed in the tensile tests. Similarly, the thermal conductivity was also directional, showing slightly higher anisotropy than the elastic modulus anisotropy. Conceptually, this study reveals the different length scales involved in thermoelastic anisotropy and provides insight into the design of liquid crystalline elastomers on demand for high frequency applications.
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＜Abstract＞