Doping-dependent ion selectivity of polyaniline membranes

Polyaniline (PAN) films were cast from a solution in N-methyl-2-pyrrolidone (NMP) and characterised by atomic force microscopy (AFM), FTIR, X-ray, TGA and DSC. Ion selectivity of the films as free-standing membranes in the electrolyte/membrane/electrolyte system was characterised by transmembrane electric potential. It was demonstrated that PAN membrane has completely different permeability and ion selectivity in the undoped and HCl-doped states. In the undoped state, the membrane is hardly permeable to inorganic ions, but still it is selective to H+. After HCl-doping transmembrane resistance decreases by a few orders of value, and the membrane becomes anion/H+-selective.