Using copper perchlorate doped liquid crystals for the detection of organophosphonate vapor

We report the use of liquid crystal 4-cyano-4′-biphenylcarbonitrile (5CB) doped with copper perchlorate as an optical sensor for detecting dimethyl methylphosphonate (DMMP) vapor. Our results show that after doping 5CB with copper perchlorate (0.05–50 mM), orientations of 5CB supported on plain glass slides gradually change from planar to homeotropic over time, and the time requires for turning homeotropic orientation increases with the decreasing concentration of copper perchlorate. When we expose a film of homeotropically oriented 5CB doped with 0.1 mM of copper perchlorate to 0.003 ppm of DMMP vapor, the optical appearance of 5CB changes from dark to bright in 2.5 min. In contrast, no response can be observed when the same film is exposed to 4500 ppm of water, 1000 ppm of ethanol or 1000 ppm of hexane. The optical response of 5CB to DMMP is fully reversible. Because DMMP is a commonly used simulant for chemical warfare agent, this work demonstrates the feasibility of using 5CB doped with copper perchlorate as a real-time gas sensor for detecting chemical warfare agents.