Ionomer-like behaviour of protonated polyaniline: Effect of ionic strength on the optical spectra

The absorbances of polyaniline (PAni) at 850 nm due to the electronic transition from a polaron band and at 130 cm-(1) due to vibrational excitation of the hydrogen bond are observed to change non-linearly with the degree of protonation. The extent of non-linearity for these changes is dependent on the ionic strength of the protonating medium. The effect of ionic strength on the bands originating from the two different types of transitions (electronic and vibrational) are found to be similar. A model has been proposed relating PAni with ionomers to account for the observations. This also provides an explanation for the formation of metallic islands in the polymer. It seems that the distribution of the dopants in the polymer matrix and the interchain interactions have a combined influence on the electronic structure of protonated PAni.