Acrylic acid and HCl-doped polyanilines were synthesized by chemical oxidat
ive polymerization. The synthesized materials were used as sensors for ammo
nia. Comparison of the responses of the two polymers reveal that the acryli
c acid-doped polymer exhibits higher sensitivity and reversibility. Further
, the resistance is observed to decrease on exposing the acrylic acid-doped
polyaniline to saturated ammonia vapors. A reversed trend is observed in t
he case of HCl-doped polyaniline. The results are explained in terms of the
differences in the chemical interactions of the two polymers with respect
to ammonia vapors. The proposed mechanism is further supported by the X-ray
diffraction and FTIR analysis. The X-ray diffractogram of acrylic acid-dop
ed polymer shows an enhancement in the crystallinity on exposure to ammonia
vapors, while the HCl-doped polymer exhibits a loss in crystallinity. The
FTIR spectra shows a higher doping level in acrylic acid doped polymer as o
bserved from the intense peak of the dopant ion at 1158 cm(-1), which is se
en to be shifted to a lower wavenumber i.e. similar to 1128 cm(-1) on expos
ing the polymer to ammonia vapors. On the other hand, in HCl-doped polyanil
ine, the peak of the dopant ion similar to 1120 cm(-1) is initially less in
tense, which is further suppressed on exposure to ammonia. Conductivity mea
surements show a large vapor-induced increase in conductivity, in the case
of ammonia-exposed acrylic acid-doped polyaniline, which results in the for
mation of a more crystalline-conducting phase. Exactly the opposite results
were obtained in the case of HCl-doped polyaniline exposed to ammonia. (C)
2001 John Wiley & Sons, Inc.