Dispersion of Multiferroic Nanoparticles in a Bent-Core Nematic Liquid Crystal: Experimental and Theoretical Study

TL;DR

This study investigates how dispersing multiferroic nanoparticles in a bent-core nematic liquid crystal affects its structural and optical properties, revealing increased order despite reduced cluster size, supported by experimental and theoretical analysis.

Contribution

It introduces a combined experimental and theoretical approach to understand the impact of multiferroic nanoparticles on bent-core nematic liquid crystals, including a new Landau-de Gennes model.

Findings

Increased orientational order parameter in doped system

Reduction of cybotactic cluster size due to nanoparticle doping

Transition temperature decreases by 1-2°C with doping

Abstract

A novel nanocomposite system has been prepared by dispersing multiferroic bismuth ferrite nanoparticles (BiFeO$_3$) in a bent-core nematic liquid crystal (8-F-OH) that exhibits cybotactic clusters. Transition temperature, optical textures, order parameter $S_m$, and dielectric spectroscopy experiments are performed in the doped system, and the results are compared with the pure one. The main experimental outcome is that the doped system has increased orientational order parameters, even though the cybotactic cluster size is reduced due to the incorporation of multiferroic BiFeO$_3$ nanoparticles. The transition temperature, as observed under polarising optical microscopy, clearly indicates a reduction of $1 - 2~ ^\circ{\rm C}$ in the doped system compared to the pure one, and we conjecture this is due to the disordering of the cybotactic cluster in the doped system. Based on the experimental findings, a Landau-de Gennes-type free energy model is developed. The model qualitatively explains the increased mean order parameter and the disordering of cybotactic clusters with increasing polarization value of nanoparticles. This is corroborated by experimental findings.