INVESTIGATION OF NEMATIC LIQUID-CRYSTALS AS SURFACE-ACOUSTIC-WAVE SENSOR COATINGS FOR DISCRIMINATION BETWEEN ISOMERIC AROMATIC ORGANIC VAPORS

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