Abstract:
Poly(pyrrole) and poly( aniline) are prepared on to electrode surface from an
aqueous solution by electrochemical oxidative polymerization of pyrrole and
aniline, respectively. Optimal electrolytic conditions for the electrosynthesis of
the studied polymers are also determined. Film of these polymers on platinum
when mounted in electrolytic solution without monomers can be
electrochemically switch between the oxidized (doped / conducting) form and
the neutral (dedoped / insulating) form. Thus prepared polymer samples
employed XRD and IR spectroscopy for their structural analysis. The d.c
conductivity and UV-Vis spectroscopic measurements are performed to have an
insight about the electrical and optical properties of the studied polymeric
materials. Effect of ambient atmosphere and heat on the structure and electrical
properties of the poly( aniline) samples are also studied.
Optimization of the electrolytic solution concentration as 0.5 M pyrrole and 0.1
M tetraethylammonium tetrafluoroborate for the electrosynthesis of
poly(pyrrole) and 0.5 M aniline and 0.8 M perchloric acid as for poly(aniline)
resulted a massive and free standing polymer on the electrode substrate. Cyclic
voltammograms both for poly(pyrrole) and poly(aniline) indicate that the
polymers can be oxidized by doping with an anions and can be neutralize by
dedoping the inserted anions. Doping of the studied samples is controlled
potentiostatically for poly(pyrrole) and galvanostatically for poly(aniline)
samples.
From IR spectra the bands, characteristics of pyrrole and aniline confirming the
presence of these monomer rings in the polymers. Absorption bands for
tetrafluoroborate and perchlorate ions are also found in the doped spectra of
poly(pyrrole) and poly(aniline), respectively. XRD spectra showed the diffused
scattering for doped and dedoped poly(pyrrole) samples indicating the
amorphous nature ofpoly(pyrrole). In contrast, crystalline peaks are observed in
the doped spectra of poly(aniline), although its dedoped state exhibits
amorphous character.
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The d.c conductivity measurements both for poly(pyrrole) and poly(aniline)
show a general trend of doping characteristics i.e., conductivity rises rapidly at
the beginning of the doping process and then shows little change even though
the polymer films become more highly doped. The conductivity of poly(pyrrole)
and poly(aniline) reached a maximum value of 3.40 x 10-1 and 45.00 x 10-1
Scm-I, respectively, which ate about three orders of magnitude higher than their
respective dedoped states.
UV-Vis spectra of poly(pyrrole) and poly(aniline) show the strong absorption
maxima in the ultra-violet region which are associated with the interband
trasition. Absorption in the visible region also indicated two other transitions
within the gap region such as : transition from valence band to upper bipolaron
antibonding level and trnnsition from valance band to bipolarOll bonding state.
Optical studies also provide the elucidation of band model for P9Iy(pyrrole) and
poly(aniline) assigning a band gap of 4.96 and 3.70 eV, respectively.
