Self-doping of polyaniline prepared with the FeCl3/H2O2 system and the origin of the Raman band of emeraldine salt at around 1375cm(-1)
Abstract
Stepwise addition of H2O2 in small portions into the polymerization mixture reduces the number of defects in polyaniline (PANI) prepared with the Fe3+/H2O2 system, although it does not eliminate them completely. PANIs slightly self-doped with phenolic groups are thus obtained, which show conductivity from 2.65 to 0.38Scm(-1) as the total H2O2/aniline mole ratio is increased from 0.125 to 1.25.
The conductivity shows a good correlation with the A(B)/A(900) UV-visible absorbance ratio of the PANI emeraldine salt form (PANI ES), much better than with the A(B)/A(Q) ratio of the corresponding emeraldine base form. This corresponds well with the assignment of the band at 900nm to polaronic transitions.
Partial self-doping of PANIs with weakly acidic phenolic groups allowed evidence to be obtained for the assignment of Raman bands at 1370cm(-1) and 734cm(-1) (for (exc) = 780nm) to vibrational modes of highly localized polarons. The presence of the band at 880cm(-1) in the IR spectra of these PANI ES samples that are totally free of sulfate ions proves that this band is associated with a vibrational mode of PANI ES and need not be assigned to a mode of HSO4- ions, as has been suggested by some authors. (c) 2015 Society of Chemical Industry