Multifrequency EPR study of metal-like domains in polyaniline

The magnetic, relaxation and electronic dynamic parameters of paramagnetic centers, polarons in crystalline domains of polyaniline doped by p-toluenesulfonic acid (PANI-TSA) being in the metallic state (“organic metal”) were studied at 3-cm (9.7 GHz) and 2-mm (140 GHz) EPR wavebands in a wide temperature range. The polarons in PANI-TSA interact strongly at magnetic fields used and demonstrate the Lorentzian single lines with the Dysonian contribution. Room temperature intrinsic conductivity of metal-like domains in air-containing PANI-TSA determined from the Dysonian spectra was ca. 4000 S/cm. This value decreases sufficiently at the sample evacuation. It was shown that polarons interact strongly and weakly below and above the critical temperature Tc, respectively, due to a phase transition that leads to an extremal temperature dependence of the polymer linewidth. As the registration frequency increases from 9.7 GHz up to 140 GHz, the Tc value is shifted from 160 K down to 130 K. Intrinsic conductivity of PANI does not correlate with its linewidth that indicates polaron localization inside crystalline domains. Charge is transferred according to the Mott variable range hopping mechanism.