Aggregation Phenomena in Lyotropic Chromonic Liquid Crystals

TL;DR

This paper investigates the aggregation behavior in lyotropic chromonic liquid crystals, modeling the system's energy to explain the formation of toroidal structures and their relation to experimental observations.

Contribution

It introduces a bi-phasic energy model combining Flory-Huggins mixing with bending and surface tension, explaining toroidal aggregation phenomena.

Findings

Minimizers of the energy are topologically equivalent to tori.

The model aligns with experimental evidence of toroidal structures.

Conditions for molecular aggregation are characterized.

Abstract

We study the aggregation phenomenon in lyotropic chromonic liquid crystals as the molecular concentration changes and condensing agents are added into the system. Using properties of the critical points of the Oseen-Frank energy of a nematic liquid crystal, combined with the geometric constraints of the hexagonal columnar chromonic phases, we show that the minimizers of the total energy are topologically equivalent to tori, in agreement with available experimental evidence on chromonic liquid crystals and DNA condensates, in viral capsids as well as in free solution. We model the system as bi-phasic, consisting of liquid crystal molecules and water, and postulate the total energy as the sum of the Flory-Huggins energy of mixing together with the bending and surface tension contributions of the liquid crystal. Two types of problems are considered, one related to finding the optimal shape of a torus, once the phase separation has occurred, and the second one that models the conditions leading to molecular aggregation. This work follows recent experimental investigations, but without addressing the topological properties of the toroidal nuclei observed and focusing on how the liquid crystal order competes with the aggregation phenomenon.