title: Waltzing route toward double-helix formation in cholesteric shells.
abstract: Liquid crystals, when confined to a spherical shell, offer fascinating possibilities for producing artificial mesoscopic atoms, which could then self-assemble into materials structured at a nanoscale, such as photonic crystals or metamaterials. The spherical curvature of the shell imposes topological constraints in the molecular ordering of the liquid crystal, resulting in the formation of defects. Controlling the number of defects, that is, the shell valency, and their positions, is a key success factor for the realization of those materials. Liquid crystals with helical cholesteric order offer a promising, yet unexplored way of controlling the shell defect configuration. In this paper, we study cholesteric shells with monovalent and bivalent defect configurations. By bringing together experiments and numerical simulations, we show that the defects appearing in these two configurations have a complex inner structure, as recently reported for simulated droplets. Bivalent shells possess two highly structured defects, which are composed of a number of smaller defect rings that pile up through the shell. Monovalent shells have a single radial defect, which is composed of two nonsingular defect lines that wind around each other in a double-helix structure. The stability of the bivalent configuration against the monovalent one is controlled by c = h/p, where h is the shell thickness and p the cholesteric helical pitch. By playing with the shell geometry, we can trigger the transition between the two configurations. This transition involves a fascinating waltz dynamics, where the two defects come closer while turning around each other.
authors: Effets Collectifs & Matière Molle (EC2M), UMR CNRS 7083 Gulliver, Ecole Supérieure de Physique et Chimie Industrielles de la ville de Paris, Paris Sciences et Lettres (PSL) Research University, 75005 Paris, France;
authors: Alexandre
authors: A
authors: Darmon
authors: Effets Collectifs & Matière Molle (EC2M), UMR CNRS 7083 Gulliver, Ecole Supérieure de Physique et Chimie Industrielles de la ville de Paris, Paris Sciences et Lettres (PSL) Research University, 75005 Paris, France;
authors: Michael
authors: M
authors: Benzaquen
authors: Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia.
authors: David
authors: D
authors: Seč
authors: Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana, Slovenia.
authors: Simon
authors: S
authors: Čopar
authors: Effets Collectifs & Matière Molle (EC2M), UMR CNRS 7083 Gulliver, Ecole Supérieure de Physique et Chimie Industrielles de la ville de Paris, Paris Sciences et Lettres (PSL) Research University, 75005 Paris, France;
authors: Olivier
authors: O
authors: Dauchot
authors: Effets Collectifs & Matière Molle (EC2M), UMR CNRS 7083 Gulliver, Ecole Supérieure de Physique et Chimie Industrielles de la ville de Paris, Paris Sciences et Lettres (PSL) Research University, 75005 Paris, France; Teresa.Lopez-Leon@espci.fr.
authors: Teresa
authors: T
authors: Lopez-Leon
keywords: chirality; geometrical frustration; liquid crystals; spherical shell; topological defect