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Séminaire de Teresa Lopez-Leon


"Waltzing defects in chiral liquid crystal shells "

Teresa Lopez-Leon

Gulliver, ESPCI.

Liquid crystals exhibit fascinating behaviors when confined to curved spaces. One of the most striking consequences is the presence of topological defects in the ground state of the system, which result from frustrations in the spontaneous liquid crystalline order. Here I will show the rich phenomenology emerging when confining a chiral liquid crystal, or cholesteric, to a spherical shell.

Our shells are droplets of cholesteric liquid crystal containing an inner aqueous core, so that the liquid crystal is confined between two spherical boundaries. We observe that the bipolar and radial configurations, intensively reported for conventional droplets, have a higher degree of complexity in shells. The bipolar configuration is replaced by a structure where the boojums are linked to a stack of disclination rings that spans the shell, while the radial configuration exhibits a double helix structure where two disclinations wind around each other, as predicted by recent numerical simulations. We also show that the position of the boojums is only controlled by the shell geometry, independently of the cholesteric pitch. To understand quantitatively this behavior, we develop a simple yet insightful theoretical framework which captures the essence of the observed phenomenology. We also show that the transition between the two configurations is governed by the confinement ratio c = h/p, where h is the average shell thickness and p is the cholesteric pitch. Finally, we perform a dynamical study of this transition, and report a fascinating defect waltz due to a chemical Lehmann effect.

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