A geometric method to determine chromonics' planar anchoring strength

TL;DR

This paper introduces a geometric method to measure the planar anchoring strength of chromonic nematic liquid crystals by analyzing droplet shapes in experiments, aiding their characterization for potential biological applications.

Contribution

The paper presents a novel geometric approach to determine chromonics' planar anchoring strength based on equilibrium droplet shapes in a thin cell, supported by experimental shape analysis.

Findings

Shape bistability in small droplets with tactoid and discoid forms

Predicted equilibrium shapes include elongated rods, discoids, and tactoids

Experimental shapes resemble elongated rods with round ends called batonnets

Abstract

Chromonic nematics are lyotropic liquid crystals that have already been known for half a century, but have only recently raised interest for their potential applications in life sciences. Determining elastic constants and anchoring strengths for rigid substrates has thus become a priority in the characterization of these materials. Here, we present a method to determine chromonics' planar anchoring strength. We call it geometric as it is based on recognition and fitting of the stable equilibrium shapes of droplets surrounded by the isotropic phase in a thin cell with plates enforcing parallel alignments of the nematic director. We apply our method to shapes observed in experiments; they resemble elongated rods with round ends, which are called batonnets. Our theory also predicts other droplets' equilibrium shapes, which are either slender and round, called discoids, or slender and pointed, called tactoids. In particular, sufficiently small droplets are expected to display shape bistability, with two equilibrium shapes, one tactoid and one discoid, exchanging roles as stable and metastable shapes upon varying their common area.