Alternating electrical conductivity of polyaniline

The ac complex conductivity sigma*( f) of polyaniline (PAN) films at different doping levels and different temperatures, in the 1-100 KHz frequency range, are reported. The results are typical of a disordered medium where the real component of ac conductivity is frequency independent at low frequencies, rising for higher values of frequencies. In order to interpret both the real and the imaginary components of sigma*( f), we developed a model which considers the doped PAN as a disordered insulating matrix, sprinkled with conductive islands generated by doping, as indicated by energy dispersed x-ray microanalysis. The conduction through the insulating matrix obeys the random free energy barrier model, while in the conductive islands a metallic frequency-independent conductivity is considered. From the fittings we obtained the activation energy value of the maximum energy barrier of the doping mechanism and estimated the concentration of hopping sites. (C) 1999 American Institute of Physics. [S0021-9606(99)70806-8].