Ferroelectric Nematic Droplets in their Isotropic Melt

TL;DR

This study combines optical microscopy and theoretical analysis to explore ferroelectric nematic liquid crystal droplets in their isotropic melt, revealing their shape, defect dynamics, and electric charge distribution under applied fields.

Contribution

It provides the first detailed experimental and theoretical insights into ferroelectric nematic droplets coexisting with isotropic melt, including their shape, defect behavior, and polarization effects.

Findings

Droplets are pancake-shaped and thinner than the sample thickness.

Defects in droplets move and split under electric fields.

Droplets drift and oscillate in response to electric fields.

Abstract

The isotropic to ferroelectric nematic liquid transition had been theoretically studied over one hundred years ago, but its experimental studies are rare. Here we present polarizing optical microscopy studies and theoretical considerations of ferroelectric nematic liquid crystal droplets coexisting with the isotropic melt. We find that the droplets have flat pancake-like shapes that are thinner than the sample thickness as long as there is a room to increase the lateral droplet size. In the center of the droplets a wing shaped defect with low birefringence is present that moves perpendicular to a weak in-plane electric field, and then extends and splits in two at higher fields. Parallel to the defect motion and extension, the entire droplet drifts along the electric field with speed that is independent of the size of the droplet and is proportional to the amplitude of the electric field. After the field is increased above 1V/mm the entire droplet gets deformed and oscillates with the field. These observations led us to determine the polarization field and revealed the presence of a pair of positive and negative bound electric charge due to divergences of polarization around the defect volume.