Vertical Orientation of Liquid Crystal on Polystyrene Substituted with n-alkylbenzoate-p-oxymethyl Pendant Group as a Liquid Crystal Precursor.

Kyutae Seo,Hyo Kang

doi:10.3390/polym13132058

Abstract

We synthesized a series of polystyrene derivatives modified with precursors of liquid crystal (LC) molecules via polymer modification reactions. Thereafter, the orientation of the LC molecules on the polymer films, which possess part of the corresponding LC molecular structure, was investigated systematically. The precursors and the corresponding derivatives used in this study include ethyl-p-hydroxybenzoate (homopolymer P2BO and copolymer P2BO#, where # indicates the molar fraction of ethylbenzoate-p-oxymethyl in the side chain (# = 20, 40, 60, and 80)), n-butyl-p-hydroxybenzoate (P4BO), n-hexyl-p-hydroxybenzoate (P6BO), and n-octyl-p-hydroxybenzoate (P8BO). A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with P2BO#, with 40 mol% or more ethylbenzoate-p-oxymethyl side groups. In addition, the LC molecules were oriented vertically in LC cells fabricated with homopolymers of P2BO, P4BO, P6BO, and P8BO. The water contact angle on the polymer films can be associated with the vertical orientation of the LC molecules in the LC cells fabricated with the polymer films. For example, vertical LC orientation was observed when the water contact angle of the polymer films was greater than ~86°. Good orientation stability was observed at 150 °C and with 20 J/cm2 of UV irradiation for LC cells fabricated with the P2BO film.

Highlights

Liquid crystals (LCs) are attractive materials, which have intermediate phase between ordinary liquids and three-dimensional solids
The LC molecules were vertically oriented in the LC cells fabricated with these polymer films when the substituent ratio was only 40 mol%. These results indicate that similarities between the chemical structure of the orientation layer and the LC molecules are favorable for the vertical orientation of LC molecules
The LC cells fabricated with polymers with 40 mol% or more of ethylbenzoate-p-oxymethyl (P2BO40, P2BO60, P2BO80, and P2BO) side groups exhibited vertical LC orientation, while the LC cells fabricated from P2BO films with less than 20 mol% of ethylbenzoate-poxymethyl side groups revealed partial LC textures with birefringence

Summary

Introduction

Liquid crystals (LCs) are attractive materials, which have intermediate phase between ordinary liquids and three-dimensional solids. Vertically oriented LC layers using polystyrene (PS) derivatives synthesized via a polymer substitution reaction have been developed for electro-optical applications, including flexible displays, owing to their advantages of low temperature processability and superior optical transparency. The vertical orientation of LC molecules in LC cells fabricated with PS derivatives substituted with natural extracts, such as capsaicin, eugenol, and vanillin, was observed when the substituent ratio was greater than 60 mol% This is due to the long alkyl groups of the natural extracts, which are related to the low surface energy owing to the steric effect of the alkyl groups on the polymer film surface [54,55,56,57]

Methods

Results

Conclusion