Horizontal transportation of a Maltese cross pattern in nematic liquid crystalline droplets under a temperature gradient

Yoshioka, Jun; Fukao, Koji

doi:10.1103/physreve.99.022702

Cited by 18 publications

(28 citation statements)

References 68 publications

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“…These authors showed that 'strong' flows can develop within the isotropic liquid around the droplets, leading to their deformation. These flows resemble very much the Marangoni flows observed around the droplets in the Lehmann experiment with emulsified cholesterics [11,15]. Because these flows are responsible for the droplet rotation in that case, one can expect that a similar effect exists in the coexistence region when an AC electric field is applied to the droplets.…”

Section: Introductionsupporting

confidence: 54%

Role of an oscillatory electric field on the Lehmann rotation of cholesteric droplets

Oswald

2020

Eur. Phys. J. E

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This paper deals with the Lehmann rotation of banded cholesteric droplets subjected to a temperature gradient when they coexist with their own isotropic liquid. I show that their angular rotation velocity increases-in absolute value-when they are subjected to an additional AC electric field in the conducting regime. This velocity increase is correlated with a prolate distortion of the droplets and the probable presence of electrohydrodynamical toroidal circulation flows inside and outside the droplets. I propose that the coupling between these flows and the director field is responsible for the increase of the angular velocity of the texture. The origin of these flows is discussed qualitatively in the framework of the leaky dielectric model by taking into account the generation of charges both in the bulk via a Carr-Helfrich mechanism (Tarasov, Krekhow and Kramer model) and at the surface of the droplet (Taylor-Melcher model).

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Section: Introductionsupporting

confidence: 54%

Role of an oscillatory electric field on the Lehmann rotation of cholesteric droplets

Oswald

2020

Eur. Phys. J. E

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“…In addition, the assumed director field could have a slight incompatibility with the real structure. Particularly, in the present study, the interface between LC and the solvent has a weak anchoring property 16,18,26,27 , which can deform the helical structure around the edge region of the pillar. For these reasons, the rotational torque and behaviour in Region-III may become different from the theoretical consideration.…”

Section: (4)mentioning

confidence: 76%

“…However, Ḟ is actually negligibly small in the present case because the dynamic (timedependent) director deformation is just scarcely observed under POM and hence not so significant. As for the dissipation function, the coupling terms between the flow and director fields can be described as [26][27][28][29][30] (…”

Section: Discussionmentioning

confidence: 99%

“…However, is actually negligibly small in the present case because the dynamic (time-dependent) director deformation is just scarcely observed under POM and hence not so significant. As for the dissipation function, the coupling terms between the flow and director fields can be described as 26 – 30 where i and j denote x , y , or z ; , and are the i -components of the positional vector, flow velocity vector and director field, respectively; , , , and are constants with the same dimension as the viscosity coefficient. For simplicity, let us assume the flow velocity vector, and the director field, where the linear flow in the z -direction at the velocity of is introduced together with the rotational flow at the angular velocity of .…”

Section: Discussionmentioning

confidence: 99%

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Differential rotation in cholesteric pillars under a temperature gradient

Yoshioka

Araoka

2020

Sci Rep

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Steady rotation is induced in cholesteric droplets dispersed in a specific liquid solvent under a temperature gradient. In this phenomenon, two rotational modes have been considered: (1) collective rotation of the local director field and (2) rigid-body rotation of the whole droplet structure. However, here we present another rotational mode induced in a pillar-shaped cholesteric droplet confined between substrates under a temperature gradient, that is, a differential rotation where the angular velocity varies as a function of the radial coordinate in the pillar. A detailed flow field analysis revealed that every pillar under a temperature gradient involves a double convection roll. These results suggested that the differential rotation in the cholesteric pillars was driven by the inhomogeneous material flow induced by a temperature gradient. The present experimental study indicates that the coupling between the flow and the director motion plays a key role in the rotation of the cholesteric droplets under the temperature gradient.

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“…When the cooling rate is less than 0.5 °C/min, no microdroplet injection was observed (Figure S4b). Note that the Marangoni force is commonly considered the driving force for the self-propulsion of droplets in immiscible liquids. ,,– However, in this work, the Marangoni force mainly contributes to the injection process, and the motion of LC droplets during the rapid cooling is rarely observed. Although the concrete mechanism requires further study, we found that rapid cooling is vital to injection rather than propulsion, avoiding the formation of steady interior conventions within liquid droplets that would lead to droplet motion.…”

Section: Resultsmentioning

confidence: 92%

Production and Reconfiguration of Double Emulsions by Temperature Control

Guo,

Wang,

Chang

et al. 2023

Langmuir

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Double emulsions are of great importance for both science and engineering. However, the production of multicore double-emulsion droplets is challenging and normally requires sophisticated microfluidic devices, which limits their availability to broader communities. Here, we propose a simple, precise, and scalable batch method for producing double emulsions with monodispersed multicores at milliliter per minute rates, using the most common means in laboratory, temperature. By rapidly cooling liquid crystal emulsions, the introduced temperature gradient around the emulsion droplets leads to the injection of monodispersed guest droplets to form double-emulsion droplets. The number of injected water droplets can be precisely controlled by adjusting the thermally induced mechanical force through the temperature difference and the cooling rate. In contrast to conventional microfluidic fabrication, this method processes all emulsion droplets simultaneously in a noncontact and in situ manner. Therefore, it has great flexibility, allows multiple processing of double emulsions of arbitrary shape, has good capacity for mass production, and offers excellent compatibility with technologies such as microfluidics. Finally, we demonstrate that temperature changes can also be used to release the inner droplets from the double emulsion. The proposed method offers a reversible tool for processing double emulsions with minimal cost and expertise and is applicable to droplet-based microsystems in materials science, photonics, sensors, pharmaceuticals, and biotechnology.

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Horizontal transportation of a Maltese cross pattern in nematic liquid crystalline droplets under a temperature gradient

Cited by 18 publications

References 68 publications

Role of an oscillatory electric field on the Lehmann rotation of cholesteric droplets

Role of an oscillatory electric field on the Lehmann rotation of cholesteric droplets

Differential rotation in cholesteric pillars under a temperature gradient

Production and Reconfiguration of Double Emulsions by Temperature Control

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