Influence of alignment layers on crystal growth of polymer-stabilized blue phase liquid crystals

Po-Ju Chen,Shih-Ya Ni,Michael Chen,Yi-Hsin Lin,Hung-Shan Chen

doi:10.1364/ome.6.001003

Po-Ju Chen, Shih-Ya Ni + Show 3 more

Open Access

https://doi.org/10.1364/ome.6.001003

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Abstract

The feature that devices based on blue phase liquid crystals (BPLCs) is free of alignment layers. However, the alignment layers could affect the morphologies of BPLC-devices as well as the electro-optical properties. In this paper, we investigate the influence of alignment layers to crystal growth of polymer-stabilized blue phase liquid crystals (PS-BPLCs). Without alignment layer, PS-BPLCs experiences both homogeneous nucleation and heterogeneous nucleation, and the morphology appears in random crystal orientations. On the contrary, when the surfaces coated with alignment layers, a heterogeneous nucleation dominates during the crystal growth process. We further proposed a possible mechanism for crystal growth under different surface condition. This study provides an alternative method to control crystal growth of PS-BPLCs, which is for facilitating many PS-BPLCs based photonic devices.

Highlights

Blue phase liquid crystal (BPLC), a phase usually existing between the cholesteric state and the isotropic state, has been investigated for many years
We found that heterogeneous nucleation, which means the PS-BPLCs grow at the interface between two different materials or phases, has capability of suppressing homogeneous nucleation in terms of grain growth and inhibition by turns
We experimentally observe the crystal growth process in three different cells, which are assembled by substrates coated with indium tin oxide (ITO) only, ITO substrates coated with parallel alignment (PA) layers, and ITO substrates coated with vertical alignment (VA) layers, respectively and proposed possible mechanism to explain the influence of alignment layer to the crystal growth of BPLCs

Summary

Introduction

Blue phase liquid crystal (BPLC), a phase usually existing between the cholesteric state and the isotropic state, has been investigated for many years. We found that heterogeneous nucleation, which means the PS-BPLCs grow at the interface between two different materials or phases, has capability of suppressing homogeneous nucleation in terms of grain growth and inhibition by turns. As a result, both of the uniformity of grains and crystal orientations are controllable and reduce hysteresis. Both of the uniformity of grains and crystal orientations are controllable and reduce hysteresis It is well-known that devices based on BPLCs or PS-BPLCs are free of alignment layers. This study extends the understanding of crystal growth of PS-BPLCs under different surface condition, and can expedite the development of many PS-BPLCs based electro-optical devices

Sample preparation and experiments

Conclusion