The ageing of polypyrrole nanotubes synthesized with methyl orange

The process of ageing of polypyrrole is accompanied by gradual changes in its chemical composition, protonation level and charge transport mechanism. Although these changes are often limiting for practical application of polypyrrole, they are still far from being understood. In our contribution, natural (i.e. ageing at room temperature) and accelerated ageing (at 120 degrees C) of polypyrrole nanotubes were studied. Natural ageing for about 3 year timespan lead to relative decrease of sample conductivity to about 0.2 of its initial sigma(0) value. Accelerated ageing caused a dramatic decrease of 7 orders of magnitude after about 1000 h accompanied by partial deprotonation and backbone oxidation as confirmed by infrared, Raman and XPS spectroscopy and elemental analysis. Occurrence of crystalline domains was attributed to residual methyl orange and was not affected by ageing. The presence of methyl orange was found crucial for improving stability of sample conductivity; it caused about 4 orders of magnitude enhanced conductivity when compared with polypyrrole without methyl orange. In macroscopic scale the conductivity loss was found to be a spatially homogeneous process as revealed by electrical tomography. With increasing ageing time, besides gradual degradation on microstructural level, a qualitative change of charge transport mechanism was found.