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Liquid crystals and anisotropic media

par Vincent Démery - publié le , mis à jour le

Cholesteric shells : disclosing the inner structure of defects

Confining liquid crystals to spherical geometries imposes topological constrains to the system that typically result in fundamentally new behaviors. Most of the studies have been focused on nematic phases. We have uncovered a number of new shell configurations, varying in number and type of defects, by adding chirality to the nematic phase (cholesteric phase).

We have studied the transition between two limit configurations :
• Monovalent shells (with a single radial defect), analogous to a Dirac monopole
• Bivalent shells (with two defects spanning the shell).

Bringing together experiments and numerical simulations, we have disclosed the complex inner structure associated to those defects and revealed that the transition involves a fascinating waltz dynamics, where the two defects come closer while turning around each other.

Two +1 topological charge defects winding together to form one single + 2 charge defect in a cholesteric liquid crystal shell

These results have been published in two papers :
• Darmon, M. Benzaquen, D. Seĉ, S. Čopar, O. Dauchot and T. Lopez-Leon "Waltzing route toward double-helix formation in cholesteric shells", PNAS, Vol. 113, 9469 (2016)
• Darmon, M. Benzaquen, S. Čopar, O. Dauchot and T. Lopez-Leon "Topological defects in cholesteric liquid crystal shells” Soft Matter, 12, 9280 (2016)