Electrochemical synthesis and electrical properties of polypyrrole

Abstract

Electrically conductive polypyrrole films were synthesized by the anodic oxidation of pyrrole monomers with p-toluenesulfonic acid electrolyte in a single compartment glass cell under various reaction conditions. The films prepared were characterized by elemental analysis, infrared spectroscopy, scanning electron microscopy, and conductivity tests. The conductivity of the films was affected by synthetic conditions such as temperature, current density, the concentration of electrolytes, and so on. With the increase in temperature, optimal current density was increased but optimal electrolyte concentration was decreased. The film prepared under the current density of 0.2$\sim$1mA/$cm^2$ at -20$^\circ$C showed a high conductivity in the range of 200$\sim$230$\Omega^{-1}cm^{-1}$. The film prepared at -20$^\circ$C showed a more flexibility and a higher electrical conductivity than those prepared at the higher temperature. The high flexibility is due to the reduction of cationic charges in the polymer chain and the high conductivity is due to the mixed-valence (redox) conduction. A highly conductive polymer showed a smoother surface and more discrete particles on it than others. It appears from the result that nucleation reaction and polymerization reaction are easily occurred at the surface of the polymer film. It suggested that a highly conductive polymer has longer $\pi$-conjugated chain without defect than others. This may be a reason why the film shows high conductivity. For both highly and weakly conductive films, the temperature dependence of conductivity was dominated by the Mott``s variable range hopping model (VRHM) over the range of 80$\sim$300 K. Various physical properties such as characteristic temperature ($T_0$), state density at Fermi level (N($E_F$)), conductivity constant ($\sigma_0$), and average hopping distance (R), were calculated from the VRH model. With the Mott``s requirements of the model, it was proved that $T_0$ was only favorable propert...