Topology-dependent self-structure mediation and efficient energy conversion in heat-flux-driven rotors of cholesteric droplets

Abstract

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.

Lehmann rotation of cholesteric droplets driven by Marangoni convection

“…The next step, once the textures have been characterized, would be to numerically solve the equations of nematodynamics in the temperature gradient for each texture. Finally, we emphasize that the mechanism proposed here explains both the Lehmann rotation recently reported by Yohioka and Araoka of cholesteric droplets dispersed in PF 6 and also the rotation of cholesteric droplets observed in the experiments of Yamamoto and Sano during their self-propulsion in an aqueous surfactant solution 28 .…”

“…This strategy, however, has failed to result in Lehmann rotation when the droplets are subjected to a temperature gradient. The situation has recently changed when experiments by Yoshioka and Araoka 6 have shown rotation of cholesteric droplets dispersed in a partially-miscible isotropic liquid. Just as in the original Lehmann experiment, rotation occurs when a temperature gradient is applied, but it is much faster than in droplets coexisting with their isotropic phase, and it can be observed at all temperatures below the clearing transition.…”

Toroidal Configuration of a Cholesteric Liquid Crystal in Droplets with Homeotropic Anchoring

“…В случае, когда ХЖК находится в замкнутой полости, ее геометрия накладывает на структуру ЖК дополнительные условия вдобавок к перечисленным выше факторам [2,3]. В свою очередь, формирующаяся в таких полостях структра влияет на оптические [4,5,6,7], фотомеханические [7,8], термомеханические [9,10], гидродинамические (microswimmer) [11] и пр. свойства капель ХЖК.…”

Spherical-cap droplets of a photo-responsive bent liquid crystal dimer

“…Cholesteric (Ch), smectic (Sm), or columnar (Col) LC systems with curved boundaries are more complicated [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], because the director structures are dominated not only by the two factors described already but also by others, such as helix formation due to the chirality or the compression elasticity due to the translational ordering with molecular length scales. The key point to be noticed here is the role played by frustration among these factors.…”

“…For instance, spherical Ch droplets show multi-dimensional twists even without the aid of surface anchoring Ito,Poy]. In other words, the use of strong anchoring may cause additional frustrations by which various complex topological states are realized in such droplets [1,[17][18][19][20][21][22][23][24]. In this sense, LC materials showing the recentlyfound twist-bend nematic (NTB) phase are attractive systems to study complex frustrations induced by the curved surface.…”