Acrylic acid doped polyaniline as an ammonia sensor

Chemically synthesised acrylic acid doped polyaniline (PANI:AA) has been ut ilised as an ammonia vapour sensor in a broad range of concentrations, viz. 1-600 ppm. The response, in terms of decrease in de electric resistance on exposure to ammonia was observed. The change in resistance, DeltaR, is fou nd to increase linearly with NH, concentration upto 58 ppm and saturates th ereafter. The decrease in resistance has been explained on the basis of rem oval of proton from the free acrylic acid (AA) dopant by the ammonia molecu les thereby rendering free conduction sites in the polymer matrix. These re sults are well supported by FTIR spectral analysis and the X-ray diffractio n studies. The FTIR spectra show a remarkable increase in benzenoid and qui noid vibrations. Also. simultaneous appearance of -COO- and ammonium ion vi brations is indicative of the interaction of ammonia molecules with acrylic acid. The degree of crystallinity was found to increase substantially upto 58 ppm concentration. (C) 2001 Elsevier Science B.V. All rights reserved.