The effects of surface morphological mechanics on liquid crystal alignment characteristics using photo-activators

Abstract

Photo-activators, which produce carbon dioxide, are highly reactive radical generators upon UV light illumination. In this study, the generated radicals selectively reacted with the polyimide (PI) main chains and created a liquid crystal alignment layer with a high level of azimuthal anchoring energy. The thickness of the photo-irradiated PI alignment layer was reduced dramatically by photo-induced radical crosslinking, which induced surface wrinkling and roughness. Moreover, the carbon dioxide and methane gases that were generated during photo-irradiation produced many micro-pores, which also attributed to holding the LC molecules tightly on the PI surfaces. The level of azimuthal anchoring energy that was obtained by photo-alignment was better than what was obtained by the rubbing method with the same PI, specifically, the maximum value of the photo-alignment with the photo-activator was 6.92 x 10⁻⁵ J/m² than 1.11 x 10⁻⁵ J/m² of the rubbing. We proposed a mechanism based on a high anchoring energy, a rough surface, a hydrophilic surface, and rapid photo-reactions.

Keywords:

• Liquid Crystal Alignment
• Photo-Activator
• Photo-Fragment Reaction
• Radical Generation
• Surface Morphology Analysis

Acknowledgment

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) by the Ministry of Education (2015R1D1A1A01059747).