Electrical conductivity of polyaniline-dodecylbenzene sulphonic acid complex: thermal degradation and its mechanism

Polyaniline (PANI) doped with dodecylbenzene sulphonic acid (DBSA) and methylbenzene sulphonic acid (MBSA) were used as model compounds to investigate thermal degradation mechanisms of electrical conductivity of PANI salts. The effects of high temperature annealing on the conductivity, thermal stability and morphology of the doped PANI were studied. Within a period of 2 h, the conductivity of the two PANI salts decreases continuously with the annealing time. The conductivity reduction also increases significantly with the annealing temperature. Both polymers show significant weight loss during the annealing, especially at 200 degreesC. The weight loss of PANI-MBSA is more pronounced than that of PANI-DBSA, while the conductivity reduction shows an opposite trend. Scanning electronic microscopy (SEM) study reveals a significant morphology change caused by the annealing. Fourier transformed infrared (FT-IR) results indicate that some dopants are converted to free acids due to the annealing. It is, therefore, suggested that in addition to cross-linking of PANI and evaporation and degradation of the dopants, the segregation of the dopants from the polymers is also an important mechanism responsible for the conductivity degradation observed. (C) 2002 Elsevier Science B. V. All rights reserved.