Liquid Crystal-Based Chemical Sensors
This chapter presents an overview of recent advances in the use of liquid crystals (LCs) for sensing of small organic molecules from vapors (chemical sensing). The fundamental phenomenon underlying the approach to LC-based sensors addressed in this chapter is an adsorbate-driven anchoring transition in a film of LC, a phenomenon that has been known since the pioneering studies in the early 1990s by Pieranski and Jerome [1–4]. Recent studies have sought to realize chemical sensors based on LCs by using combinations of chemically tailored surfaces and LCs in order to engineer highly selective adsorbate-induced ordering transitions in the LCs. We also note that cholesteric LCs have been used for chemical sensing (with a change of pitch occurring upon absorption of an analyte), but approaches to chemical sensing based on cholesteric LCs lie beyond the scope of this chapter [5–14]. Finally, a number of studies with LCs as biological sensors have been reported over the past decade; however, we do not attempt to address those advances but rather refer the interested reader to relevant literature [15–24].
Figure 15.1 depicts two examples of adsorbate-driven ordering transitions that have been utilized as the basis of chemical sensors. In the first example, intermolecular interactions between ...