Dye induced great enhancement of broadband reflection from polymer stabilized cholesteric liquid crystals

Abstract

A series of polymer stabilized cholesteric liquid crystals (PSCLCs) films were prepared from cholesteric liquid crystal (Ch‐LC) mixtures containing different components such as non‐reactive LC monomer, polymerizable monomer, chiral dopant, dye, and photoinitiator upon polymerization. The influence of the polymerizable monomer and dye of Ch‐LC mixtures on the reflection properties was investigated. The reflection bandwidth for all the samples can be increased by photo‐polymerization, and the network upon polymerization derived from two different polymerizable monomers with both one and two functional groups is more effective than that from one polymerizable monomer for broadening the reflection band. Especially, a dye‐doped Ch‐LC film can reflect incident light with the bandwidth over the wavelength range of 550–2350 nm, which is due to a greater pitch gradient formed inside of Ch‐LC film. The gradient pitch network structure was firstly demonstrated by scanning electron microscopy (SEM) with the film prepared from high diacrylate monomer concentration and subsequently proved by using a wash‐out/refill method. The nematic liquid crystals monomers was infiltrated into the polymer network that was prefabricated by removing the low molar weight LCs from the original PSCLCs film, and SEM exhibited the existence of a pitch gradient across the film thickness. The refilled nematic liquid crystals film showed broadband reflection after polymerzition, too. Copyright © 2011 John Wiley & Sons, Ltd.

Cholesteric Liquid Crystals with a Broad Light Reflection Band

“…The transfer of the method in Ref. 140 to the case of PSCLCs75, 76, 146–148 has given rise to materials that can be switched to the homeotropic transparent state and reverted to the planar reflective state upon removal of the field 75, 76, 146…”

Preparation of polymer‐stabilized cholesteric liquid crystal films capable of broadband reflection using a three‐layer system of self‐diffusion

“…The reflection bandwidth can be reduced by more than 500 nm when an AC electric field is applied and when exposed to high temperatures. Li et al prepared PSCLC films containing different compositions of nonreactive liquid crystal monomers, polymerizable monomers, chiral dopants, dyes, and photoinitiators and systematically investigated the influence of the temperature and the structure of polymerizable monomers with different functional groups on the broadband reflectance properties 34 . The experimental results demonstrate that PSCLC films prepared by polymerization of different CLC mixtures exhibit variable broadband reflectance properties, and the dye‐containing film forms a large pitch gradient inside, which reflects incident light in the 550–2350 nm band.…”

Enhanced Bandwidth Broadening of Infrared Reflector Based on Polymer Stabilized Cholesteric Liquid Crystals with Poly(N-vinylcarbazole) Used as Alignment Layer

“…Broer et al have obtained bandwidth broadening in a CLC film doped with an ultraviolet (UV) light absorbing dye, which was used to create an intensity gradient through the thickness of a solid cholesteric polymer network, resulting in a pitch gradient through the cell thickness [ 25 ]. Yang et al report a method that blended different polymerizable monomers and dye into the PSCLC system, and the broadband reflection wavelength was significantly increased to 550–2350 nm after polymerization [ 26 ]. However, the bandwidth through the above methods was static once frozen by the polymerization process, which cannot be tunable.…”