Segregation of liquid crystal mixtures in topological defects

Mohammad Rahimi,Hadi Ramezani-Dakhel,Nicholas L Abbott,Juan J De Pablo,Rui Zhang,Abelardo Ramirez-Hernandez

doi:10.1038/ncomms15064

Abstract

The structure and physical properties of liquid crystal (LC) mixtures are a function of composition, and small changes can have pronounced effects on observables, such as phase-transition temperatures. Traditionally, LC mixtures have been assumed to be compositionally homogenous. The results of chemically detailed simulations presented here show that this is not the case; pronounced deviations of the local order from that observed in the bulk at defects and interfaces lead to significant compositional segregation effects. More specifically, two disclination lines are stabilized in this work by introducing into a nematic liquid crystal mixture a cylindrical body that exhibits perpendicular anchoring. It is found that the local composition deviates considerably from that of the bulk at the interface with the cylinder and in the defects, thereby suggesting new assembly and synthetic strategies that may capitalize on the unusual molecular environment provided by liquid crystal mixtures.

Highlights

The structure and physical properties of liquid crystal (LC) mixtures are a function of composition, and small changes can have pronounced effects on observables, such as phase-transition temperatures
The Saturn ring consists of two disclination lines with a topological charge of À 1⁄2 that are bended around the spherical particle
Note that LC mixtures are widely used in commercial applications, and their physical properties depend strongly on composition, with small changes being able to compromise the isotropic to nematic phase

Summary

Introduction

The structure and physical properties of liquid crystal (LC) mixtures are a function of composition, and small changes can have pronounced effects on observables, such as phase-transition temperatures. Liquid crystals (LCs) exhibit a rich variety of defects that can be observed and even controlled experimentally Such defects are closely analogous to those encountered in cosmology, particle physics and condensed matter physics, thereby making LCs a valuable experimental testing grounds for the study of defects in a wide range of disciplines[2]. As the arguments above have all been generated on the basis of phenomenological descriptions of LCs, they have been verified by a wide range of experimental observations Such arguments, view defects as a region of space where the director changes abruptly. By simulating a mixture of 5CB (4-cyano-40-pentylbiphenyl) and 8CB (4-cyano40-octylbiphenyl), we present a previously unknown molecular view of the scalar order parameter, density, composition, biaxiality and the nematic director field inside line defects of what is perhaps the most widely studied liquid crystalline material

Methods

Results

Conclusion