Non-conducting polyaniline nanofibrils and their physico-chemical behavior

The work presented here aimed to synthesize the non-conducting form of PANI nanofibrils and to study their properties, which are determined by their chemical structure and morphology. Non-conducting PANI nanofibrils were synthesized by an alkali-based treatment process. Raman measurements revealed that synthesized PANI nanofibrils consist mainly of benzenoid units with a small number of quinoid units. Calculations based on Raman spectra show that ratio of benzenoid to quinoid units is 3:1. This ratio is 3 times higher than the characteristic/typical value for synthesized non-conducting PANI, as reported in the literature. Moreover, the photoluminescence of these non-conducting PANI nanofibrils (measured with excitation of 442 nm) possesses two maxima, with wavelengths of 550 nm and 1110 nm. These wavelengths correspond to photon energies of 2.25 eV and 1.12 eV, which resemble very long Stokes shifts of 108 nm and 658 nm, respectively. This finding has not been presented previously. However, when the excitation is performed with a 785 nm red laser, the emission spectra of non-conducting PANI nanofibrils exhibit numerous sharp emission peaks. We attribute these transitions to the chemical structure of the synthesized polymer chains and to its nanofibril morphology.