New chiral dimers consisting of a rod-like and cholesterol mesogenic units are reported to form a chiral twist-bend nematic phase (NTB *) with heliconical structure. The compressibility of the NTB phase made of bent dimers was found to be as large as in smectic phases, which is consistent with the nanoperiodic structure of the NTB phase. The atomic force microscopy observations in chiral bent dimers revealed a periodicity of about 50 nm, which is significantly larger than the one reported previously for non-chiral compounds (ca. 10 nm).

When a chiral liquid crystal is given a transport current, a unidirectional molecular motion is known to take place, which is called the Lehmann effect. In this paper, we study the mysterious heat-current-driven Lehmann effect using two types of hemispherical cholesteric droplets using polarizing, reflecting, confocal and fluorescent microscopies. Both the droplets, coexisting with the isotropic phase and contacting on a glass substrate, are characterized by the concavo-convex modulated surface and the inside orientational helix. Further, the only difference between them is the helical axis direction; i.e., one is perpendicular and the other is parallel to the substrate. Under the temperature gradient perpendicular to the substrate, the droplet whose helical axis is parallel to the heat current exhibited pure director rotation, while that with the axis perpendicular to the current rotated independently as a rigid body. In the two droplets, the rotational conversion efficiency from the temperature gradient into the angular velocity showed very different dependences on the chirality strength and on the droplets' size, suggesting that the rotations of the two droplets may be driven by independent torques with different origins. This is the first observation that the cholesteric droplets under the temperature gradient exhibit the two rotational modes, the pure director rotation and the molecular barycentric motion, which can be switched to each other by changing the heat-current direction parallel and perpendicular to the helical axis.

When heat flux is applied to a chiral liquid crystal, unidirectional rotation is induced around the flux axis, as first discovered by Otto Lehmann in 1900. In recent years, this heat-flux-induced phenomenon has been studied mostly in droplets of cholesteric liquid crystals undergoing phase transition from the isotropic to cholesteric phase, i.e., in the coexistence region, which occurs over a very narrow temperature range. Here, we report that the heat-flux-induced rotation can be stabilised by the use of a dispersion system, in which the cholesteric droplets are dispersed in a viscous and poorly miscible isotropic solvent. Interestingly, the phenomenon is found to be topology dependent. Moreover, the rotation is not only stable but also more efficient than that in the known systems. We describe in detail how the dynamics of the heat-flux-induced rotation are altered in the present dispersion system.

We found for the first time the stabilization of a double twisted structure in cholesteric liquid crystals confined to small spherical droplets under weak anchoring conditions. The direct observation of the droplets using a polarized microscope revealed the physical properties of the structure. The experimental results showed that the stability of the double twisted structure is determined by the relationship between the helical pitch length and the droplet size. We theoretically analyzed the structural stability by the calculation of the Frank elastic free energy including the surface elastic term, and succeeded in explaining the experimental results. In this paper, we concluded that the stability of the double twisted structure is determined by the competition between the surface and the bulk elasticity.

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New chiral dimers consisting of ar od-like and cholesterol mesogenic units are reported to form achiral twistbend nematic phase (N TB *) with heliconical structure.T he compressibility of the N TB phase made of bent dimers was found to be as large as in smectic phases,w hichi sc onsistent with the nanoperiodic structure of the N TB phase.T he atomic force microscopyo bservations in chiral bent dimers revealed aperiodicity of about 50 nm, whichissignificantly larger than the one reported previously for non-chiral compounds (ca. 10 nm).

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