Yuka Tabe (Waseda University) Thermo-mechanical coupling in chiral liquid crystals

Due to the broken mirror symmetry, chiral liquid crystals (LCs) possess unusual features both in static and dynamic structures. One interesting example is the unidirectional molecular rotation driven by linear flow; when a heat current[1], an electric current[2], or a diffusion current[3] is transported through a chiral LC sample, the director exhibits unidirectional rotation along the flow axis. The dynamical cross correlation in chiral LCs has been known for long years, which is recently refocused from the application point of view as soft sensors and rotors.

In this talk, we show the rotation of cholesteric droplets dispersed in the coexisting isotropic phase or in immiscible liquids under a temperature gradient[4-6]. When a heat current passed through the droplets, the constituent molecules exhibited the unidirectional rotation along the flux, the direction of which was reversed by the chirality inversion and the velocity was linear to the temperature gradient. Furthermore, the droplets showed not only the director rotation but also rigid-body rotation when they were small. Considering that the way of rotation should be determined by the competition between the external torque, the surface anchoring and the orientational elasticity, we estimated the extrapolation length and the coherent length, and successfully explained the size-dependence. The result helps the better understanding of the thermomechanical coupling in chiral LCs and will be useful for the future application.

[1] O. Lehmann, Ann. Phys. 307, 649 (1900).

[2] N. V. Madhusudana, R. Pratibha, and H. P. Padmini, Mol. Cryst. Liq. Cryst. 202, 35 (1991).

[3] Y. Tabe and H. Yokoyama, Nat. Mat. 2, 806 (2003).

[4] S. Bono, Y. Maruyama, and Y. Tabe, Soft Matter 14, 9798 (2018).

[5] K. Nishiyama, S. Bono, and Y. Tabe, Soft Matter 17, 10818 (2021).

[6] S. Takano, S. Bono, and Y. Tabe, J. Phys. Soc. Jpn. 92, 024601 (2023).