Poly(2,3-dimethylaniline) as a competent material for humidity sensor

Chemically synthesized polyaniline and its ring substituted derivatives such as poly(o-toluidine), poly(2,3-dimethylaniline) and poly(2,5-dimethylaniline) were utilized as sensors for relative humidity (RH) between 6.4% and 97.3%. The conductivity of the polymers was found to decrease on exposure to RH between 6.4% and 75.3%. However, in presence of 97.3% RH the conductivity was seen to increase. A comparison of the observed results reveals that, though each of the polymers responds to various percentages of RH, poly(2,3-dimethylaniline) shows the best response in terms of sensitivity and linear range. The percent sensitivity was found to be greater fur poly(2,3-dimethylaniline) than that for polyaniline. The observed change in conductivity as well as the degree of change in magnitude of conductivity in the polymers was supported by X-ray diffraction studies and IR spectroscopy. The X-ray analysis showed that crystallinity of the polymer changed both in the presence and the absence of a specific percent of RH. Similarly, the IR spectra exhibited variation in the peak intensities of the O-H and >N-H groups. (C) 2001 John Wiley & Sons, Inc.