Conductivity Degradation Study of polypyrrole and polypyrrole/5% w/w TiO2 nanocomposite under Heat Treatment in Helium and Atmospheric Air

E. Vitoratos, S. Sakkopoulos, E. Dalas, K. Emmanouil

The thermal aging of the d.c. electrical conductivity σ in pure polypyrrole (PPy) and in the nanocomposite PPy/5%w/w TiO₂ was investigated for thermal treatment times from 0 to 50 hours at different temperatures Τ = 100, 300 and 380 K under atmospheric air and inert He gas. In both materials the fluctuation induced tunneling of charge carriers was followed revealing a granular metal structure. The isothermal variation of σ with time under atmospheric air and inert He indicates the coexistence of two antagonistic mechanisms, the one increasing and the other decreasing σ. In XRD patterns from PPy and PPy/5%w/w TiO₂ the sharp peaks of rutile and anatase crystallographic types of TiO₂ coexist with the broad peak of amorphous PPy. The latter shifts to smaller angles with the addition of TiO₂ indicating a greater separation of pyrrole rings, which turns up to be about equal to the diameter of O^2- indicating the diffuse of oxygen from TiO₂ into PPy. SEM pictures confirm the removal of Cl^- in the form of HCl during thermal aging, a process which decreases the conductive part of the polymer and at the same time rearranges the chains. These represent two antagonistic mechanisms the first decreasing, the second increasing conductivity.