Humidity Sensitive Properties of Electronically Conductive Poly(diphenylamine sulfonic acid) and Its Block Copolymer and Blends

In this study, a water soluble conductive polymer, poly (diphenylamine sulfonic acid) was synthesized by using both chemical (PSDA) and electrochemical (EPSDA) polymerization. By the reaction of the reduced form of PSDA with poly (ethylene glycol) (PEG), a diblock copolymer (PSDA-b-PEG) was synthesized. The humidity sensing properties of PSDAs, PSDA-b-PEG, and their binary blends with PEG and commercial latex of poly (vinylacetate-co-butylacrylate) (PVAc/BuAcry) were investigated by impedance measurements. The effects of film composition, applied potential bias, alternating current frequency and polymer film thickness on electrical properties and sensitivity were determined. PSDA-b-PEG films showed high humidity sensitivity, i.e. the impedance ranged about four orders of magnitude over the relative humidity range between dry and saturated humid conditions under 0.2 V of potential bias and 100 kHz of alternating current frequency. The thin film sensor of PSDA-b-PEG copolymer has a linear response in the range from 0 to 95% relative humidity. The repeatability of the sensor responses was good enough, i.e. the relative standard deviation was less than 3% and 4% at the lowest and highest humidity levels, respectively. The hysteresis was less than 3% relative humidity for the studied sensors. The response and recovery times depend on alternating current frequency and film composition and thickness of the studied polymers; the best response and recovery times were obtained for the thinnest film of PSDA-b-PEG as 2 and 3 minutes, respectively, at 100 kHz.