Vertical Orientation of Liquid Crystal on Comb-Like 4-(trans-4-alkylcyclohexyl)phenoxymethyl-substituted Polystyrene Containing Liquid Crystal Precursor.

Kyutae Seo,Hyo Kang

doi:10.3390/polym13091404

Abstract

We synthesized a series of polystyrene derivatives modified with precursors of liquid crystal (LC) molecules, including 4-(trans-4-ethylcyclohexyl)phenol (homopolymer PECH and copolymer PECH#; # = 5, 10, 15, 20, 40, 60, and 80, where # indicates the molar fraction of 4-(trans-4-ethylcyclohexyl)phenoxymethyl in the side chain), 4-(trans-4-propylcyclohexyl)phenol (PPCH), 4-(trans-4-butylcyclohexyl)phenol (PBCH), and 4-(trans-4-amylcyclohexyl)phenol (PAmCH) via polymer modification reactions in order to investigate the orientation of LC molecules on polymer films exhibiting part of the LC molecular structure. A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with PECH#, having 15 mol% or more of 4-(trans-4-ethylcyclohexyl)phenoxymethyl side groups. In addition, the vertical orientation of LC molecules was observed in LC cells fabricated with homopolymers of PECH, PPCH, PBCH, and PAmCH. The water contact angle on the polymer films could be associated with the vertical orientation of the LC molecules in the LC cells fabricated with polymer films. For example, a vertical LC orientation was observed when the water contact angle of the polymer films was higher than ~81°. Good orientation stability was observed at 200 °C and 15 mW/cm2 of UV irradiation for LC cells fabricated with PECH films.

Highlights

Liquid crystals (LCs) are anisotropic materials which have an intermediate phase in which they demonstrate fluidity, and exceptional physicochemical characteristics due to the positional and/or orientational order of their molecules [1,2,3,4,5]
The vertical orientation of LC molecules in the LC cells fabricated with these polymer films was observed when the substituent ratio was only 15 mol%. These results suggest that the similarity between the chemical structure of the orientation layer and LC molecules can be advantageous in the vertical orientation of LC molecules
We investigated the effect of the amount of 4-(trans-4-ethylcyclohexyl)phenoxymethyl moieties in the side chain on the vertical LC orientation properties

Summary

Introduction

Liquid crystals (LCs) are anisotropic materials which have an intermediate phase in which they demonstrate fluidity, and exceptional physicochemical characteristics due to the positional and/or orientational order of their molecules [1,2,3,4,5]. Vertical LC orientation layers using PS derivatives via a polymer substitution reaction have been developed for electro-optical applications, including flexible displays, due to their advantages such as 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 larger than 60 mol% This is due to the long alkyl groups of the natural extracts, which are related to low surface energy owing to the steric effect of alkyl groups on the polymer film surface [42,43,44,45,46,47,48]. Polymers 2021, 13, 1404 tion of these polymers and the optical properties of the assembled LC cells with unrubbed polymer films were studied

Materials

Film Preparation and LC Cell Assembly

Results and Discussion

Conclusions