Improved electrical and thermal properties of polypyrrole prepared by the repetition of a combination of chemical polymerization and 2-naphthalenesulfonic acid treatment

Electrical property and thermal stability of acid-treated polypyrrole (Ppy) film, which was prepared by the repetition of chemical polymerization of pyrrole (Py) followed by dipping in an aqueous solution of citric acid/boric acid (MCB), p-toluenesulfonic acid (p-TS), 2-naphthalenesulfonic acid (2-NS), and 1,3,6-naphthalenetrisulfonic acid (NTS) were investigated. The normalized capacitance, the Cp/C0 value of capacitor fabricated with Ppy film (Ppy-II-2-NS) treated with 2-NS increased with increasing the number of times of polymerization and acid treatment, and reached 0.8 after 18 times repetition, whereas for the capacitor fabricated with Ppy film (Ppy-I) without acid treatment the Cp/C0 value stayed at a poor level of 0.4. A similar Cp/C0 = 0.8 was obtained for Ppy films treated with p-TS and NTS. The equivalent series resistance (ESR) value at 100 kHz of Ppy-II-2-NS showed a low value of 2 mΩ being about one-fifth of Ppy-I film. The normalized resistance (Rt/R0) at 150 °C indicates that the conductivity decay of the Ppy-II-2-NS/Al2O3/Al capacitor was significantly suppressed compared to the Ppy-I/Al2O3/Al capacitor. These results indicate that 2-NS treatment in the chemical polymerization process is highly effective to improve the electrical properties of Ppy/Al2O3/Al capacitor at elevated temperatures.