Humidity sensor using cross-linked copolymers containing viologen moiety

1-[3-(2-Methacryloxyerhyl dimethyl ammono)propyl] 1 '-propyl-4,4'-bipyridinium tribromide (MDAPBT) was selected as a humidity sensing monomer. n-Butyl acrylate (n-BA) and 2-(N,N'-dimethylaminoethyl)methacrylate (DAEMA) were used as a comonomer. The major ingredient of the humid membrane is the copolymers of MDAPBT with n-BA and DAEMA. The cross-linked copolymer of MDAPBT/n-BA/DAEMA = 40/30/30 showed average resistance of 1000, 52 and 3.1 K Omega at 30, 60 and 90% relative humidity (RH), respectively. Temperature dependence, frequency dependence and response time were also measured. The temperature dependence at 15-40 degreesC is -0.42 to -0.45% RH degreesC(-1) and the hysteresis falls on the range of +/-2% RH. The humidity-sensitive characteristics of the sensor did not change even after 20 min when the sensor was soaked in water. (C) 2001 Elsevier Science B.V. All rights reserved.