Polyaniline treated with organic acids: doping characteristics and stability

Polyaniline base in the form of solution, powder and film was treated with aqueous solutions of three organic acids, toluenesulfonic acid (TSA), sulfosalicylic acid (SSA) and dodecylbenzenesulfonic acid (DBSA), and HClO4. The doping characteristics and stability of these salts were studied using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy and UV-Vis absorption spectroscopy. Polyaniline salts in N-methylpyrrolidinone (NMP) solution readily undergo deprotonation, whereas the DBSA-protonated salt in CHCl3 is stable even under near-UV irradiation. The protonation levels achievable when the base powder is treated with the organic acids are comparable with that obtained with HClO4. When the protonation of the base powder is carried out in mixtures of organic acids and HClO4, the organic acid anions are selectively incorporated into the salt. However, in the case of films, protonation by the organic acids is hampered by the large size of the anions. When salt films are cast from salt solutions, the larger anions are retained better than the ClO4− anions when these films are treated with water. The organic anions also decompose at a higher temperature than the ClO4− anions.