Self-Assembly of an Equimolar Mixture of Liquid Crystals and Magnetic Nanoparticles

Gaurav P Shrivastav

doi:10.3390/cryst11070834

Abstract

We studied the equilibrium self-assembly of an equimolar mixture of uniaxial liquid crystals (LCs) and magnetic nanoparticles (MNPs) using molecular dynamics simulations. The LCs are modeled by ellipsoids interacting via Gay–Berne potential, and MNPs are represented by dipolar soft spheres (DSS). We found that the LCs show isotropic, nematic, and smectic phases when the mixture is compressed at a fixed temperature. The DSS form chain-like structures, which remain randomly oriented at low densities where the LCs are in the isotropic phase. At intermediate and high densities, the DSS chains align along the nematic and smectic directors of LCs. We found that the DSS inside a chain follow a ferromagnetic ordering. However, the mixture does not show a significant macroscopic magnetization. The extent of nematic order in the DSS remains very similar to the LCs in intermediate densities. At high densities, the DSS have a lower extent of nematic order than the LCs. The structure of the LC–DSS mixture was further analyzed via projected pair correlation functions for distances parallel and perpendicular to directors in the nematic and smectic phases.

Highlights

To identify different orientationally ordered phases, we investigated the variation of the nematic ordering of each component of the liquid crystals (LCs)–dipolar soft spheres (DSS) mixture as a function of density
To summarize, using extensive molecular dynamics simulations, we have presented a study on the self-assembly of a 50:50 binary mixture of liquid crystals and magnetic nanoparticles
We identified different phases using nematic order parameters for LCs

Summary

Introduction

Inclusions of nanoparticles in a liquid crystalline matrix have attracted much research attention in the past few years [1,2]. Much of the recent studies have focused on using MNPs to introduce functionalities to liquid crystals [5], as the coupling of magnetic nanoparticles to the external magnetic field [11] can be utilized to control the orientation of the LC director. Recent computer simulations and experimental studies have demonstrated that the small inclusion of magnetic nanoparticles strongly affects the isotropic to nematic (I–N) phase transition in LCs in the presence of an external magnetic field [34,38,39]. We found that the LC–DSS mixture shows the isotropic phase at low densities where the LCs and DSS chains remain randomly orientated.

Simulation Details

Results

Discussion