Trapping of isotropic droplets by disclinations in nematic liquid crystals controlled by surface anchoring and elastic constant disparity

TL;DR

This study investigates how isotropic droplets nucleate and position themselves near disclinations in nematic liquid crystals, revealing that elastic constant disparities and surface anchoring control droplet displacement, which can inform microscale design.

Contribution

It demonstrates that elastic constant disparity, especially the difference between bend and splay constants, is crucial for predicting droplet positioning near disclinations, challenging the common one-constant approximation.

Findings

Droplets shift away from disclination cores with increasing temperature.

The shift is determined by the director field and elastic properties.

Elastic constant disparity explains the observed droplet behavior.

Abstract

Linear defects such as dislocations and disclinations in ordered materials attract foreign particles since they replace strong elastic distortions at the defect cores. In this work, we explore the behavior of isotropic droplets nucleating at singular disclinations in a nematic liquid crystal, predesigned by surface photopatterning. Experiments show that in the biphasic nematic-isotropic region, although the droplets are attracted to the disclination cores, their centers of mass shift away from the core centers as the temperature increases. The shift is not random, being deterministically defined by the surrounding director field. The effect is explained by the balance of interfacial anchoring and bulk elasticity. An agreement with the experiment can be achieved only if the model accounts for the disparity of the nematic elastic constants; the so-called one-constant approximation, often used in the theoretical analysis of liquid crystals, produces qualitatively wrong predictions. In particular, the experimentally observed shift towards the bend region around a +1/2 disclination core can be explained only when the bend constant is larger than the splay constant. The described dependence of the precise location of a foreign inclusion at defect cores on the elastic and surface anchoring properties can be used in the rational design of microscale architectures.