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Title: Lehmann rotation of cholesteric droplets driven by Marangoni convection
Author: Oswald, Patrick
Ignés i Mullol, Jordi
Dequidt, A.
Keywords: Cristalls líquids
Liquid crystals
Issue Date: 28-Mar-2019
Publisher: Royal Society of Chemistry
Abstract: We show experimentally and theoretically that the Lehmann effect recently observed by Yoshioka and Araoka (Nat. Commun., 2018, 9, 432) in emulsified cholesteric liquid crystal droplets under temperature gradients is due to Marangoni flows rather than to the thermomechanical or chemomechanical couplings often invoked to explain the phenomenon. Using colloidal tracers we visualize convection rolls surrounding stationary cholesteric droplets in vertical temperature gradients, while a shift in the position of internal point defects reveals the corresponding inner convection in nematic droplets thermomigrating in a horizontal temperature gradient. We attribute these phenomena to the temperature dependence of the surface tension at the interface between these partially-miscible liquids, and justify their absence in the usual case of purely lyophobic emulsions. We perform a theoretical analysis to help validate this hypothesis, demonstrating the strong dependence of the precession velocity on the configuration of the cholesteric director field.
Note: Versió postprint del document publicat a:
It is part of: Soft Matter, 2019, vol. 15, num. 12, p. 2591-2604
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ISSN: 1744-683X
Appears in Collections:Articles publicats en revistes (Ciència dels Materials i Química Física)

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