Preparation of polyanilines doped in mixed protonic acids: Their characterization by X-ray photoelectron spectroscopy and thermogravimetry

Abstract

A comparative study of polyaniline chemically prepared and simultaneously doped in protonic acid mixtures is presented. As the resultant polyaniline salts (PANI salts) are insoluble, solid-state techniques such as X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), derivative thermogravimetry (DTG) and elemental analysis have been applied to study the dopant environment as well as the electronic and chemical structure of the polymers. Both XPS and TG/DTG indicate that in the presence of competing acids, the stronger acid component is preferentially incorporated over the others. No advantage can be gained by the use of mixed-acid systems. XPS confirms that ring substitution by the dopant and the degree of protonation can be accurately measured based on the percentage of charged nitrogen in the N 1s envelope. Previous methods based on the total halogen content can lead to serious errors. TG results suggest an upper application temperature limit of about 150°C, at which point elimination of dopant occurs with loss of conductivity.