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New Insights on the Fast Response of Poly(Ionic Liquid)s to Humidity: The Effect of Free-Ion Concentration

Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen 361005, China
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These authors equally contributed to this work.
Nanomaterials 2019, 9(5), 749; https://doi.org/10.3390/nano9050749
Received: 4 May 2019 / Accepted: 13 May 2019 / Published: 16 May 2019
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Abstract

The swelling mechanism is widely used to explain the response of ionic liquids (ILs) or poly(ionic liquid)s (PILs) to moisture. While a fairly broad consensus has been attained, there are still some phenomena that are not well explained. As a complement to the swelling mechanism, we systematically studied the free volume theory in the rapid response and recovery of PIL humidity performance. We chose poly(1-ethyl-3-vinylimidazolium bromide) (PIL-Br), poly(1-ethyl-3-vinylimidazolium tetrafluoroborate) (PIL-BF4) and poly(1-ethyl-3-vinylimidazolium bis(trifluoromethane sulfonimide)) (PIL-TFSI) as model materials and investigated the impact of PIL structure including anion type, film thickness and affinity to moisture on performance to obtain the humidity sensing mechanism for PILs based on free volume theory. Hence, we can combine free volume theory with the designed PIL structures and their affinity with moisture to obtain a high concentration of free ions in PIL sensing films. Furthermore, the PIL humidity sensors also show fast, substantial impedance changes with changing humidity for real-time monitoring of the human respiratory rate due to a fast response and recovery performance. Therefore, our findings develop a new perspective to understand the humidity performance of PILs based on free volume theory, resulting in fast response and recovery properties realized by the rational design of PIL sensing films. View Full-Text
Keywords: poly(ionic liquid)s; humidity sensing; free-ion concentration; fast response and recovery; respiratory rate monitoring poly(ionic liquid)s; humidity sensing; free-ion concentration; fast response and recovery; respiratory rate monitoring
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Nie, J.; Xiao, S.; Tan, R.; Wang, T.; Duan, X. New Insights on the Fast Response of Poly(Ionic Liquid)s to Humidity: The Effect of Free-Ion Concentration. Nanomaterials 2019, 9, 749.

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