Inversion ring in chromonic twisted hedgehogs: theory and experiment

ABSTRACT

Twisted hedgehogs are defects in spherical cavities with homeotropic anchoring for the nematic director that arise when twist distortions are sufficiently less energetic than splay (and bend) distortions. They bear a characteristic inversion ring, where the director texture changes the sense it spirals about the centre of the cavity. This paper applies a quartic twist theory recently proposed to describe the elasticity of chromonics to explain a series of inversion rings observed in spherical microcavities containing aqueous solutions of SSY at two different concentrations. The theory features a phenomenological length a, whose measure is extracted from the data and shown to be fairly independent of the cavity radius, as expected for a material constant.

GRAPHICAL ABSTRACT

KEYWORDS:

• Chromonic liquid crystals
• elastic theory
• elastic constants
• twisted hedehog
• inversion ring
• SSY

Acknowledgments

The UNICAL Group acknowledges financial support through the Italian PRIN 2022 - PNRR Project No. P2022HM5E4 on Chirality induction in water-based self-assembling materials.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1. The droplets observed in [17] are in the biphasic region of phase space, where nematic and isotropic phases of the solution coexist in equilibrium, although at different concentrations, higher in the nematic ($c_{\mathrm{N}}$), lower in the isotropic ($c_{\mathrm{I}}$); see Figure 4(b). If in [17] $\mathit{c}>c_{\mathrm{I}}$ is the concentration at which the solution is prepared, then the concentration in the twisted tactoids would be $c_{\mathrm{N}}>\mathit{c}$.

Additional information

Funding

The work was supported by the Ministero dell’Istruzione, dell’Università e della Ricerca [P2022HM5E4].