Liquid crystals are unique molecules whose properties can be exploited to make vapor phase detectors. Analytes change the orientation of liquid crystals at the microscopic level, which can be observed macroscopically using crossed polarizing sheets. The liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) was coated on to surface substrates with hydrogen bond donors. Vapor analytes acting as hydrogen bond acceptors adsorb on the substrate, changing the orientation of 5CB. The detection limit of an analyte was measured via its partial pressure. Analytes with greater dipole moments are detected at lower partial pressures. For analytes with similar dipole moments, larger molecules are detected at lower pressures than smaller molecules. Comparing the detection limits of the various analytes, dipole moment and molecular size are the major factors for determining the sensitivity of the detector with respect to a given analyte.

Detection of various vapors using liquid crystals on different substrates

241st National Meeting (2011)

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