Irreversible visual sensing of humidity using a cholesteric liquid crystal

Abstract

Irreversible optical sensing of humidity by a doped cholesteric liquid crystal is achieved by using a thin film of nematic host E7 with a binaphthylorthosilicate ester as dopant (guest). The film changes its color from blue (to green to orange to red) to colorless when exposed to humidity as the dopant is hydrolyzed.

Chiral-nematic liquid crystals as one dimensional photonic materials in optical sensors

“…17 A chiral binaphtalene dithiol was used as the dopant which in the presence of a small amount of catalyst (e.g. triethylamine (TEA)) can be oxidized to the disulde dopant.…”

Optical Acetone Vapor Sensors Based on Chiral Nematic Liquid Crystals and Reactive Chiral Dopants

“…[18] Phenylhydrazine (PH), which is capable of hydrogen-bonding to the TADDOL, is expected to have a high reactivity and selectivity towards ketones. The specific TADDOL-PH complex chosen is shown in Figure 1, and consists of (4R,5R)-2,2-Dimethyl-α,α,α´,α´-tetra(2-naphthyl)dioxolane-4,5-dimethanol complexed to PH.…”

“…[18] This sensor operated on the basis of a reactive chiral dopant in a nematic LC matrix that irreversibly reacted with water vapor, resulting in a change in the reflection band of the chiral nematic liquid crystals which was attributed to a change in the helical twisting power (HTP) of the dopant.…”

Isotropic-nematic transition and cholesteric phases of helical Yukawa rods

“…2,3 This property is the basis for numerous applications on the market as well as for ideas of future applications that involve chiral liquid crystals, as e.g., sensors which change colour if the pitch reflects a change of the chemical environment, the humidity, or the strain on a material. [4][5][6] Thermotropic chiral liquid crystals can be made from synthesized molecules. A few out of many examples are chiral biphenyls, 7 bis-(binaphtylenedioxy)silane, 5 ester derivatives of hydroxypropylcellulose, 8 P6-M, 9 or copolymers consisting of γ-benzyl glutamate and γ-alkyl glutamate.…”

“…[4][5][6] Thermotropic chiral liquid crystals can be made from synthesized molecules. A few out of many examples are chiral biphenyls, 7 bis-(binaphtylenedioxy)silane, 5 ester derivatives of hydroxypropylcellulose, 8 P6-M, 9 or copolymers consisting of γ-benzyl glutamate and γ-alkyl glutamate. 10 But also natural chiral mesogens can be found, e.g., DNA, fd virus, and cellulose nanocrystals (CNC).…”