Investigation of nematic liquid crystals as surface acoustic wave sensor coatings for discrimination between isomeric aromatic organic vapors

Abstract

The use of thermotropic nematic liquid crystals (LC) as surface acoustic wave (SAW) vapor sensor coatings were investigated. Responses to four pairs of isomeric aromatic organic vapors were measured using two LC coatings and four isotropic polymer coatings. In most cases, the LC coatings showed higher sensitivity toward the more rod-like isomer within a pair due to the anisotropic nature of the deposited LC films. However, the importance of vapor-coating functional-group interactions as mediating factors in the sensor responses was evident in several cases. Incorporation of an LC coating into a four-sensor array improved the discrimination between isomers relative to an array employing only isotropic coatings. A persistent decline in the sensor baseline signal and vapor sensitivity observed over time with both LC coatings could be attributed to evaporative loss and/or changes in the elastic stiffness of the coatings.