Acrylic acid doped polyaniline as an ammonia sensor

Chemically synthesised acrylic acid doped polyaniline (PANI:AA) has been utilised as an ammonia vapour sensor in a broad range of concentrations, viz. 1–600 ppm. The response, in terms of decrease in dc electric resistance on exposure to ammonia was observed. The change in resistance, ΔR, is found to increase linearly with NH3 concentration upto 58 ppm and saturates thereafter. The decrease in resistance has been explained on the basis of removal of proton from the free acrylic acid (AA) dopant by the ammonia molecules thereby rendering free conduction sites in the polymer matrix. These results are well supported by FTIR spectral analysis and the X-ray diffraction studies. The FTIR spectra show a remarkable increase in benzenoid and quinoid vibrations. Also, simultaneous appearance of COO− and ammonium ion vibrations is indicative of the interaction of ammonia molecules with acrylic acid. The degree of crystallinity was found to increase substantially upto 58 ppm concentration.