(355a) Liquid Crystal Based Optical Sensors for Detection of Aliphatic Amines In Air

Prompt detection of aliphatic amines is an important task in environmental monitoring of air pollutants and quality control in food industry. In this presentation, a new type of liquid crystal (LC) based optical sensor with fast bright-to-dark response to butylamine in vapor phase will be discussed. We first report orientational behaviors of a thin film of lauric aldehyde (LA) doped liquid crystal, 4-cyano-4′-pentylbiphenyl (5CB), in three different configurations (air/LC/air, glass/LC/glass, and air/LC/glass) and study the effect of LA on the orientational behaviors 5CB at different interfaces. Our result shows that at the LC/air interface, the LC orientation is homeotropic when the LA concentration is below 0.5 wt%. In contrast, at the LC/glass interface, the LC orientation is homeotropic when the LA concentration is above 0.5 wt%. Moreover, because LA is reactive to butylamine, when we exposed 0.1 wt% LA-doped LC to 10 ppmv of butylamine vapor, the LC undergoes a rapid bright-to-dark optical response within 2 min. This response is caused by the orientational transition triggered by the reaction between LA and butylamine. In contrast, undoped LC did not show such response. This study shows the active role of LA dopant in determining the orientations of LC at two different interfaces, and its potential application in developing LC based gas sensors.