Localized and long-distance charge hopping in fresh and thermally aged conductive copolymers of polypyrrole and polyaniline studied by combined TSDC and dc conductivity

The charge trapping centers in fresh and thermally aged conductive polyaniline-polypyrrole copolymers (starting from pure polyaniline and ending in pure polypyrrole by steps of 10 wt%) were studied by thermally stimulated depolarization current (TSDC) spectroscopy and dc conductivity measurements. One low temperature (115-135 K) relaxation mechanism appears in polyaniline-rich copolymers and disappears after thermal anneal. It is attributed to polaron trapping in the vicinity of chlorine anion dopants. Another relaxation mechanism operates close to room temperature and is related to conformational relaxation, which corresponds to the influence of the annihilation of the conformons on the conduction mechanism. The relaxation is sensitive to thermal aging as a result of the thermal annealing on the conductivity. The temperature derivative of the dc conductivity supports the latter assertion. The activation energy values were obtained as a function of composition for both fresh and heated samples. The TSDC spectroscopy is a sensitive tool which is an alternative to the standard conductivity studies for the characterization of polypyrrole-polyaniline conductive copolymers and the study of the thermal degradation.