Conductivity mechanism of polyaniline organic films: the effects of solvent type and casting temperature

In this work, we report a study of the effect of the solvent type and the casting temperature on the electrical properties of pure fully doped conducting polymer films (polyaniline, PANI). PANI was dispersed in two different solvents (dichloroacetic acid (DCAA), and a mixture of dichloro-acetic acid and formic acid (DCAA-FA)). Previous work showed that at around 318 K, a second order liquid-liquid structural transition occurs in the dispersions. Consequently, we have chosen three different casting temperatures (298 'room temperature', 318 and 353 K). The electrical properties of the cast films were investigated in the frequency range 100 Hz-1 MHz. The temperature was varied between 20 and 300 K. We found that the dc conductivity is governed by Mott's three-dimensional variable range hopping model for the PANI/DCAA films and by a fluctuation induced tunnelling model (FIT) for the PANI/DCAA-FA films. The different Mott and FIT parameters have been evaluated. The dependence of such values on the processing parameters is discussed. The x-ray diffraction technique was also used. A reasonable correlation between microstructure and electrical properties was found. Furthermore, the films cast at the structural transition temperature had the lowest conductivity.