Rebirth of Liquid Crystals for Sensoric Applications: Environmental and Gas Sensors

Abstract

Films and droplets of liquid crystals may soon become an essential part of sensitive environmental sensors and detectors of volatile organic compounds (VOCs) in the air. In this paper a short overview of recent progress in the area of sensors based on liquid crystals is presented, along with the studies of low molar mass liquid crystals as gas sensors. The detection of VOCs in the air may rely on each of the following effects sequentially observed one after the other: (i) slight changes in orientation and order parameter of liquid crystal, (ii) formation of bubbles on the top of the liquid crystalline droplet, and (iii) complete isotropisation of the liquid crystal. These three stages can be easily monitored by a photo camera and/or optical microscopy. Detection limits corresponding to the first stage are typically lower by a factor of at least 3–6 than detection limits corresponding to isotropisation. The qualitative model taking into account the reorientation of liquid crystals is presented to account for the observed changes.

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

“…For the fabrication of well‐defined topographies at the nano or microscales, different coating layers have been explored, such as rubbed polyimide, [ 134–136 ] or gold‐coated topographies [ 46 ] which typically promote a uniform planar orientation of the LC (Table 2). For example, Kieser et al [ 135 ] explored analytes and LC interactions via surface plasmon resonance (SPR).…”

Thermotropic Liquid Crystal-Assisted Chemical and Biological Sensors

“…Cholesteric LCs may provide relatively inexpensive, efficient and highly sensitive gas or environmental sensors [ 4 , 12 , 87 , 88 ] based on the ability of cholesteric phases to selectively reflect polarized light. An important application could be to detect the presence of specific volatile organic compounds (VOC) in the human body that can serve as a biomarker for certain diseases, such as lung cancer and diabetes [ 89 , 90 , 91 , 92 ].…”

“…The unique combination of LC responsiveness to the environment and the striking optical effects that allow the rapid visualization of this response facilitates the use of LCs in sensing applications. The LC responds to several different classes of molecules, including surface-active agents such as lipids and surfactants [ 5 , 6 , 7 , 8 , 9 ] and non-surface-active molecules such as gas vapors [ 10 , 11 , 12 , 13 ] and can be tailored to respond only to specific antigens [ 9 , 10 , 14 , 15 , 16 , 17 ].…”

Responsive Liquid‐Crystal‐Clad Fibers for Advanced Textiles and Wearable Sensors

“…As demonstrated before, LCs covered with a thin polymer sheet can also sense volatile organic compounds (VOCs) due to the decrease of the phase transition temperature when LC absorbs VOC . We note that LCs are not sensitive to water vapor, which has an advantage in wearable application where exposure to humidity is likely.…”