Physical properties and thermal transition of polyaniline film

Abstract

The effect of solvent and dopant on the thermal transition of polyaniline (PANI) has been investigated principally by dynamic mechanical analysis (DMA). Solvent (NMP) containing film was found to exhibit three thermal transitions in tanδ curve (142, 198, and 272°C). The two lower transitions were disappeared when NMP was removed. Hence, the third peak was suggested to be real glass transition of PANI. The shape of DMA spectra was varied with thermal curing temperature, which is directly related to NMP content. Two other peaks seemed to be due to the evaporation of solvent existing as different environment (free NMP and hydrogen-bonded NMP), which was traced by TGA, FT-IR, and DMA with altering the curing temperature. It was suggested that the third peak was composed of cross-linking reaction between adjacent chains as well as glass transition of polyaniline backbone. NMP free films were prepared by two methods (repeating doping–dedoping cycle and thermal curing). In these films, only one tanδ was observed at over 250°C. When the NMP free film was doped, the DMA peak observed over 250°C was broadened and shifted toward lower temperature.