Quantum-Dots Dispersed Bent-core Nematic Liquid Crystals and Cybotactic Clusters: Experimental and Theoretical Insights

TL;DR

This paper investigates how quantum-dot doping affects the order, dielectric properties, and cybotactic clusters in bent-core nematic liquid crystals through experiments and a theoretical Landau-de Gennes model.

Contribution

It provides new experimental data and a theoretical framework for understanding the impact of quantum-dot doping on bent-core liquid crystals, especially on order parameters and cluster sizes.

Findings

Quantum-dot doping reduces the nematic order parameter.

Doping decreases cybotactic cluster size.

Doping alters dielectric and optical properties.

Abstract

We study a quantum-dots (QDs) dispersed bent core liquid crystalline system in planar geometry and present experimental measurements of the order parameter, dielectric dispersion and absorption spectra, optical textures, with attention to variations with temperature. A bent core liquid crystal (LC) 14-2M-CH$_3$ is used as the host material and CdSe/ZnS core-shell type QDs are used as the dopant. The nematic (N) phase exhibited by the pristine (undoped) LC 14-2M-CH$_3$ contains cybotactic clusters, which are retained by its QDs incorporated LC nanocomposite. Our notable findings concern the reduction of the orientational order parameter of the QDs dispersed LC system compared to its pristine counterpart, at fixed temperatures, and a reduction of the size of the cybotactic clusters due to the incorporation of QDs. The reduced order parameter for the doped system is accompanied by reduced birefringence, increased activation energy and a qualitative reduction in the dielectric anisotropy. We complement the experiments with a novel Landau-de Gennes type free energy for a doped bent core LC system, that qualitatively captures the doping-induced reduced order parameter and its variation with temperature. The dependency of the mean order parameter on several other factors (e.g. cluster size, coupling parameter) are also analyzed.