Polyaniline–silver composites prepared by the oxidation of aniline with silver nitrate in solutions of sulfonic acids

Aniline was oxidized with silver nitrate in aqueous solutions of sulfonic acids: camphorsulfonic, methanesulfonic, sulfamic, or toluenesulfonic acids. Polyaniline–silver composites were produced slowly in 4 weeks in good yield, except for the reaction, which took place in sulfamic acid solution, where the yield was low. Polyaniline in the emeraldine form was identified with UV–visible, FTIR, and Raman spectra. Thermogravimetric analysis was used to determine the silver content, which was close to the theoretical prediction of 68.9 wt.%. Transmission electron microscopy demonstrated the presence of silver nanoparticles of ca 50 nm average sizes as the dominating species, and hairy polyaniline nanorods having diameter 150–250 nm accompanied them. The highest conductivity of 880 S cm⁻¹ was found with the composite prepared in methanesulfonic acid solution. Its conductivity decreased with temperature increasing in the 70–315 K range, which is typical of metals such as silver. The conductivity of composites prepared in solutions of other acids was lower and increased with increasing temperature. Such dependence is typical of semiconductors, reflecting the dominating role of polyaniline in the conductivity behaviour. It is proposed that interfaces between the polyaniline matrix and dispersed silver nanoparticles play a dominating role in macroscopic level of conductivity.