MEMBRANE-PROPERTIES OF POLYMER-FILMS - THE ACID-DOPING REACTION OF POLYANILINE

The protonation/deprotonation reaction of polyaniline in the emeraldine oxidation state (PANI-E) is discussed on the basis of membrane-equilibrium considerations. The important role of the partitioning of H+ between the polymer and the bathing solution is pointed out. The concentration of (free) H+ in the polymer phase is used as a parameter in formulating the dissociation equilibrium of the Bronsted acid (PANI-E)H+. It is shown that the pK(a) value determined for this dissociation equilibrium, pK(a) almost-equal-to 5, is practically constant for all experimental conditions considered in this work. However, the pH of the bathing solution which leads to a defined protonation state of the PANI-E may vary widely depending on the partitioning equilibrium for H+. This fact is demonstrated experimentally, and the experimental findings are shown to agree with theoretical predictions based on estimated and experimentally determined Donnan potentials.