Using Liquid Crystals as Optical Gas Sensors to Detect Thiol Vapors

摘要

We show that the optical texture of a layer of liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) supported on a thiol-sensitive layer can be applied to detect 1-octanethiol and other vaporous thiols with high specificity. As demonstrated inour ellipsometry and XPS results, a thiol-sensitive layer comprising a layer of (PEI) and copper ions is capable ofoxidizing thiols to disulfides and immobilizing them on the surface. Because of the hydrophobic hydrocarbon chain of 1-octanethiol, the immobilization of 1-octanethiol lowers the surface energy. Thus, after a thin layer of 5CB is supportedon the surface, the lower surface energy causes 5CB to adopt different orientations in regions where copper ions weredeposited. Because 5CB is a birefrigent material, different orientations of 5CB also result in distinct optical textures,which are visible to the naked eye under a pair of polarizers.