Cholesteric liquid crystals for solvent vapour detection ? Elimination of cross sensitivity by band shape analysis and pattern recognition

Dickert, Franz L.; Haunschild, A.; Hofmann, Peter

doi:10.1007/bf00323506

Cited by 39 publications

(28 citation statements)

References 19 publications

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“…The incorporation of chiral LC systems in gas sensing devices ( Table 5 ) typically takes advantage of the fact that the presence of solvent vapors can result in either a change of the helical twisting power of the chiral dopant due to reaction with the analyte or physical swelling of the system with a change of order in the LC phase, which ultimately changes the helical pitch due to absorption of the analyte. Both mechanisms lead to a shift of the selective reflection band which can be observed with the naked eye [ 146–152 ] ( Figure ).…”

Section: Functional Liquid Crystal Materialsmentioning

confidence: 99%

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

Esteves

Ramou

Porteira

et al. 2020

Advanced Optical Materials

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Fast, real‐time detection of gases and volatile organic compounds (VOCs) is an emerging research field relevant to most aspects of modern society, from households to health facilities, industrial units, and military environments. Sensor features such as high sensitivity, selectivity, fast response, and low energy consumption are essential. Liquid crystal (LC)‐based sensors fulfill these requirements due to their chemical diversity, inherent self‐assembly potential, and reversible molecular order, resulting in tunable stimuli‐responsive soft materials. Sensing platforms utilizing thermotropic uniaxial systems—nematic and smectic—that exploit not only interfacial phenomena, but also changes in the LC bulk, are demonstrated. Special focus is given to the different interaction mechanisms and tuned selectivity toward gas and VOC analytes. Furthermore, the different experimental methods used to transduce the presence of chemical analytes into macroscopic signals are discussed and detailed examples are provided. Future perspectives and trends in the field, in particular the opportunities for LC‐based advanced materials in artificial olfaction, are also discussed.

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Section: Functional Liquid Crystal Materialsmentioning

confidence: 99%

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

Esteves

Ramou

Porteira

et al. 2020

Advanced Optical Materials

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“…The response is due to the ability of certain gas molecules, even at low concentration, to strongly influence the liquid crystal self-assembly [40,[42][43][44][45], triggering a reorientation of the liquid crystal director [32,34,43,44], a change in period of the supramolecular helix of shortpitch cholesterics [19,36,42,[46][47][48], or even complete loss of long-range ordering [11]. In particular, Abbott and his group [35,39,[43][44][45] demonstrated the capability of nematic LCs as sensors for detecting nerve agents at concentrations as low as part per billion.…”

Section: Introductionmentioning

confidence: 99%

Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature

Sharma

Lagerwall

2016

Liquid Crystals

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Non-woven mats comprised of liquid crystal-functionalised fibres are coaxially electrospun to create soft gas sensors that function non-electronically, thus requiring no power supply, detecting organic vapours at room temperature. The fibres consist of a poly(vinylpyrrolidone) (PVP) sheath surrounding a core of nematic 4-cyano-4ʹpentylbiphenyl (5CB) liquid crystal. Several types of mats, containing uniformly cylindrical or irregular beaded fibres, in uniform or random orientations, are exposed to toluene vapour as a representative volatile organic compound. Between crossed polarisers all mats respond with a fast (response time on the order of a second or faster) reduction in brightness during gas exposure, and they return to the original state upon removal of the gas almost as quickly. With beaded fibres, the response of the mats is visible even without polarisers. We discuss how variations in fibre spinning conditions such as humidity level and the ratio of core-sheath fluid flow rates can be used to tune fibre morphology and thereby the response. Considering future development perspectives, we argue that fibres turned responsive through the incorporation of a liquid crystal core show promise as a new generation of sensors with textile form factor, ideal for wearable technology applications. ARTICLE HISTORY

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“…In most cases, these sensors operate by the absorption of the analyte causing swelling which in turn alters the cholesteric pitch. Such sensors have been previously described for alcohols, [11] amines, [12,13] VOCs [14][15][16] and gases like oxygen and carbon dioxide. [17] These optical sensors can have a high sensitivity but are often also cross-sensitive to similar molecules.…”

Section: Introductionmentioning

confidence: 99%

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

Cachelin

Green

Peijs

et al. 2016

Advanced Optical Materials

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Accurate monitoring of exposure to organic vapors, such as acetone, is an important part of maintaining a safe working environment and adhering to long-and short-term exposure limits.Here, a novel acetone vapor detection system is described based on the use of a reactive chiral dopant in a nematic liquid crystal thin film, which can accurately monitor the total exposure over a given timeframe through changes in the reflection band of the film. It was found that films exposed to 1000 parts per million by volume (ppmv) of acetone vapor for two hours exhibited a shift in reflection band of 12 nm, with smaller shifts observed at lower concentrations of acetone. Such sensors have potential applications in industrial hygiene.

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Cholesteric liquid crystals for solvent vapour detection ? Elimination of cross sensitivity by band shape analysis and pattern recognition

Cited by 39 publications

References 19 publications

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature

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

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