Spiraling Defect Cores in Chromonic Hedgehogs

TL;DR

This paper compares classical and quartic twist theories for chromonic liquid crystals, showing they predict different defect core sizes and structures in spherical confinement, which can help experimentally distinguish between the theories.

Contribution

It demonstrates how defect core predictions differ between theories, providing a means to experimentally differentiate classical and quartic twist models for chromonics.

Findings

Quartic twist theory predicts larger defect cores (~tens of microns).

Director field lines form Archimedean spirals in quartic twist theory.

Classical theory predicts smaller, logarithmic defect cores.

Abstract

An elastic quartic twist theory has recently been proposed for chromonic liquid crystals, intended to overcome the paradoxical conclusions encountered by the classical Oseen-Frank theory when applied to droplets submerged in an isotropic fluid environment. However, available experimental data for chromonics confined to cylindrical cavities with degenerate planar anchoring on their lateral boundary can be explained equally well by both competing theories. This paper identifies a means to differentiate these theories both qualitatively and quantitatively. They are shown to predict quite different core defects for the twisted hedgehogs that chromonics generate when confined to a fixed spherical cavity with homeotropic anchoring. In the quartic twist theory, the defect core is estimated to be nearly one order of magnitude larger (tens of microns) than in the other and, correspondingly, the director field lines describe Archimedean spirals instead of logarithmic ones.