Shapes and singularities in triatic liquid crystal vesicles

TL;DR

This paper investigates the equilibrium shapes of triatic liquid crystal vesicles, revealing they form octahedral structures with six +1/3 defects, advancing understanding of shape formation in complex liquid crystalline systems.

Contribution

It introduces the order parameter for triatic liquid crystals, constructs the associated free energy, and proves the equilibrium shape of triatic vesicles is octahedral with six defects.

Findings

Triatic vesicles form octahedral shapes with six +1/3 defects.

The equilibrium shape is independent of vesicle scale.

Constructed the order parameter and free energy for triatic LC.

Abstract

Determining the equilibrium configuration and shape of curved two-dimensional films with (generalized) liquid crystalline (LC) order is a difficult infinite dimensional problem of direct relevance to the study of generalized polymersomes, soft matter and the fascinating problem of understanding the origin and formation of shape (morphogenesis). The symmetry of the free energy of the LC film being considered and the topology of the surface to be determined often requires that the equilibrium configuration possesses singular structures in the form of topological defects such as disclinations for nematic films. The precise number and type of defect plays a fundamental role in restricting the space of possible equilibrium shapes. Flexible closed vesicles with spherical topology and nematic or smectic order, for example, inevitably possess four elementary strength $+1/2$ disclination defects positioned at the four vertices of a tetrahedral shell. Here we address the problem of determining the equilibrium shape of flexible vesicles with generalized LC order. The order parameter in these cases is an element of $S^1/Z_p$, for any positive integer $p$. We will focus on the case $p =3$, known as triatic LCs. We construct the appropriate order parameter for triatics and find the associated free energy. We then describe the structure of the elementary defects of strength $+1/3$ in flat space. Finally, we prove that sufficiently floppy triatic vesicles with the topology of the 2-sphere equilibrate to octahedral shells with strength $+1/3$ defects at each of the six vertices, independently of scale.