Large rewritable liquid crystal pretilt angle by in situ photoalignment of brilliant yellow films

Colin P. McGinty,Christopher M. Spillmann,Jakub Kołacz

doi:10.1063/5.0068726

Abstract

The ability to control the alignment of liquid crystals (LCs) is a challenge that is near-universal in LC research and applications. While several practical solutions exist for controlling the azimuthal (in-plane) alignment of LCs at an interface, control over the polar, or pretilt angle of the LC often requires a combination of materials or expensive and intricate processing. Here, we introduce a method for exerting control over large pretilt angles utilizing a two-step exposure method applied to Brilliant Yellow (BY) photoalignment films. We demonstrate that BY photoalignment films have the unique ability to enforce a large range of pretilt angles spanning homeotropic (90°) and planar (0°) anchoring conditions at the LC-substrate interface. The alignment is stable over time, rewritable, and patternable. Ultimately the control established here provides a powerful and low-cost means to align and take full advantage of the anisotropic and electro-optic properties of LCs for a wide range of applications.

Highlights

Y Chigrinov et al was a two-step exposure where the first exposure was linearly polarized, resulting in reorientation of the azo-dye perpendicular to the polarization axis for control of the azimuthal orientation
We introduce a method for exerting control over large pretilt angles utilizing a two-step exposure method applied to Brilliant Yellow (BY) photoalignment films
We demonstrate that BY photoalignment films have the unique ability to enforce a large range of pretilt angles spanning homeotropic (90) and planar (0) anchoring conditions at the liquid crystals (LCs)-substrate interface

Summary

Introduction

Y Chigrinov et al was a two-step exposure where the first exposure was linearly polarized, resulting in reorientation of the azo-dye perpendicular to the polarization axis for control of the azimuthal orientation. 33 utilizing a thin film of the azodye Brilliant Yellow (BY) as an alignment material and the oblique-exposure method originally described by Chigrinov et al.20 This represented a 5Â increase in both the magnitude and tunability of previously reported pretilt angles using a photoalignment approach.

Results

Conclusion