Optical detection of organic vapors using cholesteric liquid crystals

Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature

“…We are currently experiencing an increasing interest in gas sensors based on liquid crystals (LCs) [32][33][34][35][36][37][38][39][40][41], functioning at room temperature, requiring no energy supply as they are powered by thermal energy alone, and delivering a strong optical response that is easily detected without complex spectroscopic equipment. The response is due to the ability of certain gas molecules, even at low concentration, to strongly influence the liquid crystal self-assembly [40,[42][43][44][45], triggering a reorientation of the liquid crystal director [32,34,43,44], a change in period of the supramolecular helix of shortpitch cholesterics [19,36,42,[46][47][48], or even complete loss of long-range ordering [11].…”

“…The response is due to the ability of certain gas molecules, even at low concentration, to strongly influence the liquid crystal self-assembly [40,[42][43][44][45], triggering a reorientation of the liquid crystal director [32,34,43,44], a change in period of the supramolecular helix of shortpitch cholesterics [19,36,42,[46][47][48], or even complete loss of long-range ordering [11]. In particular, Abbott and his group [35,39,[43][44][45] demonstrated the capability of nematic LCs as sensors for detecting nerve agents at concentrations as low as part per billion.…”

75-3: Chemical Gas Sensors using Chiral Nematic Liquid Crystals

“…We define shift from original wavelength to shorter wavelength as "blue-shift" and longer wavelength as "red-shift". The primary composition of nematic LCs consisted of (1) Shiff-bases (azomethine), (2) Demus esters, (3) tolans (diphenylacetylene), (4,5) phenylcyclohexyls, (6) biphenyls, and (7) bicyclohexanes. We named them LC (1) to (7) and their primary molecular structures are shown in Table 1.…”

“…Recently, studies have shown that cholesteric liquid crystals (CLCs) have great potential to be gas sensors for pathology examination and hazardous gases detection [3,4]. It is well known that the peak wavelength of selective reflection (O max ) of CLCs changes upon interaction with an adsorbed gas [5].…”

Chemical gas sensors using chiral nematic liquid crystals and its applications

“…Recent studies have shown that cholesteric liquid crystals (CLCs) have great potential to be used as gas or environmental sensors . The peak wavelength of selective reflection (λ max ) of CLCs changes upon interaction with an adsorbed gas …”