Chromonic Twisted Hedgehogs.

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• Silvia Paparini (Università degli Studi di Pavia)
• Wednesday 23 August 2023, 14:00-15:00
• Seminar Room 2, Newton Institute.

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USM - Uncertainty quantification and stochastic modelling of materials

Chromonic liquid crystals (CLCs) are lyotropic materials which are attracting growing interest for their adaptability to living systems. To describe their elastic properties, the classical Oseen-Frank theory, which posits a stored energy quadratic in the gradient of the director filed n, requires anomalously small twist constants and (comparatively) large saddle-splay constants, so large as to violate one of Ericksen’s inequalities, which guarantee that the Oseen-Frank energy density is bounded below. While such a violation does not prevent the existence and stability of equilibrium distortions in problems with fixed geometric confinement, the study of free-boundary problems for droplets has revealed a number of paradoxical consequences. A CLC droplet tactoidal in shape is predicted by the classical theory to be unstable against shape changes: it would split indefinitely in smaller tactoids while the total energy plummets to negative infinity. To overcome these difficulties, a novel elastic theory that extends for chromonics the classical Oseen-Frank stored energy by adding a quartic twist term has been proposed. The total energy of droplets is bounded below in the quartic twist theory, and paradoxes evaporate. The aim of this talk is to identify a means to differentiate these theories both qualitatively and quantitatively on the basis of the different structures they predict when CLCs are confined to fixed spherical cavities with homeotropic anchoring.Co-Author: Epifanio G. Virga.

This talk is part of the Isaac Newton Institute Seminar Series series.

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