Surface-Resistance-Type Humidity Sensor based on Sulfonated Polyimides

Abstract

Sulfonated polyimides (SPIs) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride, sulfonated diamines such as 4,4'-bis(4-aminophenoxy)biphenyl-3,3' -disulfonic acid and nonsulfonated diamines. Surface-resistance-type humidity sensors were prepared by coating the SPI solutions onto comb-shaped electrodes on ceramic support plates, and their sensor properties were investigated. With increasing the relative humidity RH from 20% to 90 %, the resistance R of the SPI sensors decreased by three orders in magnitude. The SPI sensors displayed excellent durability toward high temperature and high humidity and also toward water. The 90% response time was 1-2 min for humidification process and about 5 min for dehumidification. Hysteresis of R vs. RH relationship in humidification and dehumidification cycles was rather large because of slower molecular relaxation of polymer chains in the dehumidification process. The present SPI sensors have high potential of new applications based on the advantage of high water durability.