Double-twist cylinders in liquid crystalline cholesteric blue phases observed by transmission electron microscopy.

Shu Tanaka,Ryusuke Kuwahara,Yuto Kawata,Masanori Ozaki,Ryuji Nishi,Hiroyuki Yoshida

doi:10.1038/srep16180

Abstract

Cholesteric blue phases are liquid crystalline phases in which the constituent rod-like molecules spontaneously form three-dimensional, helical structures. Despite theoretical predictions that they are composed of cylindrical substructures within which the liquid crystal molecules are doubly twisted, real space observation of the arrangement of such structures had not been performed. Through transmission electron microscopy of photopolymerized blue phases with controlled lattice plane orientations, we report real space observation and comparison of the lattice structures of blue phases I and II. The two systems show distinctly different contrasts, reflecting the theoretically predicted, body centred and simple cubic arrangement of the double-twist cylinders. Transmission electron microscopy also reveals different tendencies of the two blue phases to align on unidirectionally rubbed surfaces. We thus show that TEM observation of alignment-controlled, photopolymerized liquid crystals can be a powerful tool to investigate complex liquid crystalline order.

Highlights

Cholesteric blue phases are liquid crystalline phases in which the constituent rod-like molecules spontaneously form three-dimensional, helical structures
The substrates impose molecular alignment parallel to the substrate, and orients the [100] direction normal to the substrates as the sample is heated from the cholesteric phase or cooled from the isotropic phase
The sample was heated and cooled repetitively within the corresponding blue phases (BPs) temperature ranges to obtain the [100] orientation across the whole sample, and irradiated by a strong UV light source to quench the molecular orientation

Summary

Introduction

Cholesteric blue phases are liquid crystalline phases in which the constituent rod-like molecules spontaneously form three-dimensional, helical structures. Despite theoretical predictions that they are composed of cylindrical substructures within which the liquid crystal molecules are doubly twisted, real space observation of the arrangement of such structures had not been performed. Through transmission electron microscopy of photopolymerized blue phases with controlled lattice plane orientations, we report real space observation and comparison of the lattice structures of blue phases I and II. The two systems show distinctly different contrasts, reflecting the theoretically predicted, body centred and simple cubic arrangement of the double-twist cylinders. The current understanding of the BP structure is based on a theoretical model which has been shown to minimize the free-energy associated with director distortions[2,14,15] In this model, the liquid crystal molecules form a cylindrical substructure within which the director is www.nature.com/scientificreports/. We show that TEM observation of alignment-controlled, photopolymerized liquid crystals can be a powerful tool to investigate complex liquid crystalline order

Methods

Results

Conclusion