Probing molecular ordering in the HCl-doped polyaniline with bulk and nanofiber morphology by their thermal behavior

Conducting polymers are an amazing class of materials, which provide new approaches in material design. The study of the thermal stability of polyaniline (PANI) is of great importance since heating is the initial step in several polymer processing methods. Concerning the studies of PANI's thermally induced structural changes, it has been observed that structural changes lead to the formation of phenazine-like structures or induce the thermal dedoping depending on the morphology and doping level, however, it was not completely clear the reason why some polymers presented the dedoping and others the cross-linking reaction after heating. In this paper, the influence of the morphology (bulk or nanofibers) on the thermal behavior of doped PANI (PANI-ES) have been investigated using the mass spectrometry-coupled thermogravimetric analysis, Raman spectroscopy and scanning electron microscopy. Our data have shown that nanofibers of PANI-ES are resistant to the thermal induced dedoping process and the major structural change have been the formation of high amount of phenazine-like segments, while for bulk PANI-ES, the dedoping process has been favored. The amount of phenazine-like segments induced by heat was dependent not only the presence of the polaronic segments but also on the molecular ordering.