Detection of volatile organic chemicals by using liquid crystals

Detection of volatile organic chemicals by using liquid crystals

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The detection of volatile organic compounds (VOCs) is drawing much attention in numerous aspects. It is not only highly utilised in the field of detection of toxic and flammable gases but also in the field of disease diagnosis and healthcare. To date, much research has been done by using liquid crystals (LCs). In this chapter, in addition to introducing various prior arts, we investigated the structural dependence of LC materials which have been hardly studied so far. In particular we focused on the use of chiral nematic LCs which show selective reflection and clarified the relationship between these molecular structures and the shift in their reflection spectrum as a result from contact with VOCs. We also propose a mechanism to explain the red- or blue-shift in the peak wavelength of the selective reflection spectrum. Furthermore, enhancement of the sensitivity and the selectivity of this VOC detection method are discussed.

Chapter Contents:

  • 19.1 Introduction
  • 19.2 Use of LCs as gas sensors
  • 19.2.1 Lyotropic LCs
  • 19.2.2 Nematic LCs
  • 19.2.3 Cholesteric LCs
  • 19.2.4 Chiral nematic LCs
  • 19.3 Molecular structure of chiral nematic LC gas sensors
  • 19.3.1 Chemical structure of LCs
  • 19.3.2 Substituted functional group
  • 19.3.3 Chiral dopant
  • 19.3.4 Dielectric anisotropy of LC materials
  • 19.3.5 Enhancement of sensitivity and selectivity of gas detection
  • 19.3.6 Mechanism of selective reflection peak wavelength shift
  • Red shift
  • Blue shift
  • 19.3.7 Characteristics of chiral nematic LCs
  • 19.4 Conclusion
  • References

Inspec keywords: reflectivity; nematic liquid crystals; chirality; organic compounds; chemical sensors

Other keywords: volatile organic compounds; toxic gases; blue-shift; chiral nematic LCs; flammable gases; VOC detection method; red- shift; liquid crystals; molecular structures; volatile organic chemicals; structural dependence

Subjects: Liquid crystals (optical materials); Chemical sensors; Chemical sensors

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