The electrical properties for polyaniline (PAn) were investigated as a function of doping acids and temperature. The dopants used were dodecylbenzene sulfonic acid (DBSA), p-toluene sulfonic acid (pTSA) and HCl.
The electrical conductivity and thermal stability were strongly dependent on the doping acids. It was explained by the facts that the stable structure and large molecular weight of dopant favored highly stable conductivity.
The conductivity of PAn-DBSA increased linearly from $1.1\times10^{-4}$ to $3.0\times10^{-1}S/cm$ on thermal heating upto 140℃, but decayed to ca. $10^{-5}S/cm$ above 200℃. X-ray and FT-IR spectroscopic results gave a suggestion that the conductivity increased with the temperature by an additional doping process in which DBSA molecules entangled at first diffused to the doping site by the thermal motion and formed the increased orderings. PAn-pTSA showed the most stable conductivity of $10^{-2}S/cm$ upto at 180℃. The conductivity of PAn-HCl decayed dramatically in air than argon, suggesting that the effects of air oxidation on the degradation could not be negligible during the thermal aging. For PAn-HCl, the conductivity decreased mainly because of the evaporation of HCl as the temperature increased. In contrast, for PAn-pTSA and PAn-DBSA, the degradation of dopants and the decomposition of PAn-dopant complex made doping level lower, dropping their conductivity.
Thermal stability of PAn depends on molecular weight and structural stability of dopants. As the pTSA and DBSA dopant degradation temperature are 300℃, it was confirmed that conductivity decayed at a lower temperature than pTSA and DBSA degradation temperature due to a complex degradation between PAn and dopants.
Cyclic voltammetric results showed the electroactivity was strongly dependent on the electronic properties of PAn. The high conductivity is responsible for the better electroactivity of PAn.
