Electronic interactions within composites of polyanilines formed under acidic and alkaline conditions. Conductivity, ESR, Raman, UV-vis and fluorescence studies

The properties of two forms of polyaniline (PAni) synthesised under acidic and basic conditions have been investigated both individually and as combined complexes. The PAni polymerised within alkaline media was redox inactive and non-conducting while the PAni emeraldine salt (ES) was electroactive and conducting. Raman, electron spin resonance, UV-Vis and fluorescence spectroscopies were used to monitor the changes in electronic properties of these conducting polymer composites. Solution cast films of alkaline synthesised (A-PAni) with the PAni ES resulted in an increase in the high spin polaron population suggesting that it acts as a pseudodopant. The ability of the A-PAni to increase and maintain the population of the polaron charge carrier was confirmed by UV-vis and Raman spectroscopy. Significantly, the presence of the A-PAni in PAni ES helped to sustain higher electrical conductivities at loading levels that were well below the percolation threshold of an insulating polystyrene sulfonate polymeric oligomer model. Fluorescence studies indicated that the A-PAni was fluorescent. However, mixtures of A-PAni with the PAni ES resulted in quenching of the A-PAni emission. The quenching process was observed to involve both static and dynamic processes, with the static quenching being dominant. These results suggest that the two polymers are strongly associated with each other when in the solid state. In stark contrast, the alkaline synthesized PAni did not influence the electrochemical properties of the emeraldine salt. These results deviate significantly from the expected outcome of the addition of an insulating A-PAni additive and highlight the unusual interactions occurring between PAni and its alkaline analogue.