Effect of hygroscopicity of insulating unit of polymer composites on their response to relative humidity

The effect of hygroscopicity of the insulating unit of polymer composites on their response to relative humidity has been investigated. The composites examined were the poly(o-aminophenol) (PoAP) composites with poly(vinyl pyrrolidone) (PVP), poly(acrylic acid) (PAA), poly(ethylene oxide) (PEO), and poly(methyl methacrylate) (PMMA) in which the hygroscopicity of these insulating polymers decreases in the sequence PAA>PVP>PEO>PMMA. The electrical conductivity of the PoAP/PVP composite was proportional to relative humidity covering more than four orders of magnitude. This result is explained on the basis of salt-base transition of conducting polymer in the composite which on reflection depends on the presence of weakly and strongly bound water. The PoAP composite with hydrophilic PAA holds a large amount of strongly bound water, and as a consequence PoAP is completely transformed to the salt form at humidity higher than 70%, resulting in the approach to a constant conductivity at the high level of conduction. On the other hand, the nonlinear dependence of the conductivity upon the change in humidity was observed for the PoAP/PEO and PoAP/PMMA composites on the first run of measurement, which was attributed to a lesser amount of strongly bound water in the composite. (C) 2000 The Electrochemical Society. S0013-4651(99)07-102-5. All rights reserved.