Extremely Deformable, Transparent, and High-Performance Gas Sensor Based on Ionic Conductive Hydrogel

Abstract

Fabrication of stretchable chemical sensors becomes increasingly attractive for emerging wearable applications in environmental monitoring and health care. Here, for the first time, chemically derived ionic conductive polyacrylamide/carrageenan double-network (DN) hydrogels are exploited to fabricate ultrastretchable and transparent NO 2 and NH 3 sensors with high sensitivity (78.5 ppm −1 ) and low theoretical limit of detection (1.2 ppb) in NO 2 detection. The hydrogels can withstand various rigorous mechanical deformations, including up to 1200% strain, large-range flexion, and twist. The drastic mechanical deformations do not degrade the gas-sensing performance. A facile solvent replacement strategy is devised to partially replace water with glycerol (Gly) molecules in the solvent of hydrogel, generating the water−Gly binary hydrogel with 1.68 times boosted sensitivity to NO 2 and significantly enhanced stability. The DN-Gly NO 2 sensor can maintain its sensitivity for as long as 9 months. The high sensitivity is attributed to the abundant oxygenated functional groups in the well-designed polymer chains and solvent. A gas-blocking mechanism is proposed to understand the positive resistance shift of the gas sensors. This work sheds light on utilizing ionic conductive hydrogels as novel channel materials to design highly deformable and sensitive gas sensors.

Progress in hydrogels for sensing applications: a review

“…The HG was mechanical tested, the sensor responses were proved to be rapid, reversible and reproducible. Wu et al proposed another innovative method for NO 2 and NH 3 detection based on double-network hydrogels [59]. We have previously introduced this category of hydrogels with their advantages such as improved mechanical properties respect classical hydrogels structure.…”

“…(c) Responses' comparisons to 2 ppm NO 2 vs service time for DN with/without rehydration and DN-Gly. (d) Representation of the water retention ability of DN-Gly and the bond formation between Gly and NO 2 .Reprinted with the permission of the American Chemical Society[59].…”

Properties of conductive polymer hydrogels and their application in sensors

“…(Reproduced from Ref. , with permission from [2018 American Chemical Society]) (g) The general sensing mechanism of PTS − PAni. (h) Sensor responses in different concentrations of putrescine.…”

“…Lately, a double‐network (DN) hydrogel sensor based on PAM and carrageenan was developed by Wu et al ., which shows excellent sensitivity to NH 3 and NO 2 as well as mechanical robustness, stretchability (up to 1200% strain) …”

“…Lately, a double-network (DN) hydrogel sensor based on PAM and carrageenan was developed by Wu et al, which shows excellent sensitivity to NH 3 and NO 2 as well as mechanical robustness, stretchability (up to 1200% strain). 127 Apart from its high sensitivity and stretchability, the sensor can also improve the water retention ability, which is of great significance for high-performance gas sensors. With gas diffusing into the hydrogel, the movability of K + and Cl − ions is hindered, causing an increase of resistance [ Fig.…”