AC dielectric relaxation of lightly hydrochloric-acid(HCl)-doped polyanilines

The AC dielectric response of lightly hydrochloric-acid( HCl)-doped polyani line (PAN) films is studied. The dielectric constant and the conductivity o f PAN samples with different doping levels are measured as functions of the frequency and the temperature. The experiments are carried out in the freq uency range from 10 Hz to 2 MHz and the temperature range from 78 K to 300 K. The frequency dependence of the dielectric constant is analyzed in terms of a dipolar - or a conductivity - relaxation mechanism. The relation sigm a(omega)approximate to sigma(0)omega(s) is observed for the frequency depen dence of the AC conductivity. The AC dielectric relaxation time is estimate d from the maximum peak of the dielectric loss. The loss peak appears at lo wer frequency as the pH level increases, which is explained by pair approxi mation for the AC transport phenomenon. With normalization of the dielectri c loss, all data points fit in a characteristic curve, which implies that t he mechanism of dielectric loss does not Vary with temperature and pH. The activation energy of the systems is estimated from the temperature dependen ce of the relaxation time or the dielectric constant. The activation energy increases as the pH level increases, which indicates that the barrier heig ht for AC transport of the systems can be controlled through doping. We pre sent the AC conductivity as a function of doping level for different freque ncies.