2-(Dimethylamino) ethyl methacrylate was copolymerized with butyl methacrylate and then quaternized with 1,4-dibromobutane to obtain a resistive-type cross-linked polyelectrolyte humidity-sensitive material. The humidity sensors based on the cross-linked polyelectrolyte were exposed to various vapors. The impedance changed from 107 Ω to 103 Ω between 33 and 95% RH after exposure to air, acetone, and ammonia vapors. However, when the sensors were exposed to ethanol vapor, the variation of the impedance with relative humidity was three orders of magnitude (107–104 Ω) in the same relative humidity range. Surface morphology of the sensors, and response-recovery time, at various vapor environments were also measured and estimated.
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