Resistive type NO2 gas sensing in polymer-dispersed liquid crystals with functionalized-carbon nanotubes dopant at room temperature

Abstract

The embedding of liquid crystal (LC) droplets into polymer matrices yields polymer-dispersed liquid crystals (PDLCs), which play an important role in the formation of mechanically resistant films for flexible photonic devices. Despite the fact that PDLCs respond to a variety of physical and chemical stimuli, LCs have had limited success in detecting environmental pollutants due to a lack of reactive functional groups in their structures. In this work, we execute the idea of integrating functionalized carbon nanotubes (f-CNTs) into PDLCs to accelerate the absorption of gas molecules at room temperature (RT). The proposed f-CNT-PDLC sensor device was prepared by depositing the composite mixture onto an interdigitated electrode substrate and carrying out phase separation under UV light exposure. Compared to the pure PDLC device, the proposed device exhibited a response of ~12.9 % and 1 % for 100 and 5 ppm of NO 2 gas, and a linear relationship was obtained with gas concentrations. Furthermore, this device displayed a good reproducibility over five cycles, exhibiting an excellent selectivity against other interfering gases, such as H 2 S, CO, H 2 , and NH 3 . The boosted response was attributed to charge transport between the NO 2 gas molecules and the f-CNTs, which was detected by measuring the change in electrical resistance caused by the f-CNTs, in addition to the orientational phase modulation of the f-CNTs and the LCs within a droplet. Our experimental results revealed that the proposed f-CNT-doped PDLCs are promising candidates for sensing various physical and chemical stimuli. • An f-CNT-doped PDLC sensor device was developed for NO 2 gas detection. • The f-CNT dopant significantly improved the sensing performance of the PDLC device. • A difference in the droplet configuration was identified with NO 2 gas molecules. • A fast and specific sensing response was achieved with proposed f-CNT-PDLC sensor.