Polymer stabilization of electrohydrodynamic instability in non-iridescent cholesteric thin films.

Yu-Cheng Hsiao,Wei Lee

doi:10.1364/oe.23.022636

Abstract

A non-iridescent cholesterol liquid crystal (CLC) thin film is demonstrated by using the polymer-stabilized electrohydrodymanic (PSEHD) method. The photopolymerized cell made from a CLC/monomer mixture exhibits an optically stable gridlike pattern. The helical axis of thus-formed CLC is aligned with the hydrodynamic flow induced by a space charge motion, and the arrayed CLC grid configuration renders a wide viewing angle thanks to the limited color shift at various lines of sight. The formation of the PSEHD structure was verified with polarized optical microscopy, ascertaining that the electrohydrodymanic pattern can be photo-cured or stabilized. The PSEHD CLC is simple to fabricate and potentially suitable for applications in wide-viewing-angle or non-iridescent devices.

Highlights

Cholesteric liquid crystals (CLCs) are intriguing optical materials that possess unique physical and mechanical properties such as dielectric anisotropy, birefringence, optical bistability, Bragg reflection, and flexibility for photonic device applications
A non-iridescent cholesterol liquid crystal (CLC) thin film is demonstrated by using the polymer-stabilized electrohydrodymanic (PSEHD) method
The photopolymerized cell made from a CLC/monomer mixture exhibits an optically stable gridlike pattern

Summary

Introduction

Cholesteric liquid crystals (CLCs) are intriguing optical materials that possess unique physical and mechanical properties such as dielectric anisotropy, birefringence, optical bistability, Bragg reflection, and flexibility for photonic device applications. Typical to CLCs is a gridlike pattern (GP) even though CLCs exhibit a few distinct patterns contingent on the pitch length [20,21] These effects are connected with EHD convection owing to the anisotropies of the dielectric constant and conductivity in the mesogenic materials. In contrast to the EHD observations mentioned above, the CLC fabricated in this work contains a rather small amount of photo-curable prepolymer This novel approach permits the stabilization of the GP (and other EHD instability patterns in general) by means of photopolymerization of the multicomponent precursor, thereby minimizing color shift for a non-iridescent structure

Experiment

Results and discussion

Conclusions