PROTONATION AND ELECTROCHEMICAL REDOX DOPING PROCESSES OF POLYANILINEIN AQUEOUS-SOLUTIONS - INVESTIGATIONS USING IN-SITU FTIR-ATR SPECTROSCOPY AND A NEW DOPING SYSTEM

Polyaniline (PANI), one of the most interesting members of the group o f conducting polymers, has been the subject of intense experimental an d theoretical studies because of its outstanding behaviour during elec trochemical redox processes and during changes of pH. In this work the electrochemical doping and protonation processes of PANI are describe d by using in situ FTIR-ATR and a new doping system NaReO4/HReO4. Cycl ic voltammetry shows that above ca. pH 4 only one wave response can be obtained. With increasing acidity of the electrolyte, a two-wave resp onse develops, the splitting of the waves occurring at pH ca. 3.5-4. B y in situ measurements during the base-acid transition process, a dist inct picture of protonation of different forms of PANI has been obtain ed. A scheme for the dopant concentration, as a function of the electr ode potential and pH, is presented. The results show that the amount o f anions involved in the doping and dedoping processes depends on the pH and the potential. Maximum doping occurs at the intermediate oxidiz ed metallic state. During both processes the electronic structure of t he polymer and also the number of protons bound to nitrogen atoms are altered. The mechanisms of the changes under different redox and acid- base conditions are described.