Interaction of hazardous gases with liquid crystals for optical gas sensing applications

Liquid crystals (LCs) are exceptionally sensitive materials for optical gas sensing due to their normal optical properties of anisotropy and sensitivity to interfacial perturbations. When interacting with LC interfacial surfaces and optical textures, hazardous gases such as nitrogen dioxide (NO₂), sulfur dioxide (SO₂), carbon monoxide (CO), and a variety of volatile organic compounds (VOCs) cause changes in the anchoring state and optical properties of LCs that can be detected using polarization-based optical techniques. This review will examine recent literature on LC/gas interactions, optical transduction principles, surface functionalization techniques, device topologies, and methods for measuring the performance of LC-based gas sensing devices. Other topics included are recent developments in image processing for optical signal detection, nanomaterials used in LC-based sensors, LC droplet array technology, along with the challenges and the future direction of research in LC/gas optical sensing devices.