Polyaniline film: reaction with Fe3+ and H+ permeability

This paper describes the redox reaction of PAN films with FeCl3 in the presence of different HCl concentrations. The reaction kinetics is characterised by two phases and is highly dependent on the solution pH and preliminary doping of the PAN film. In the initial phase at high Fe3+ concentration it is pseudo-first-order with respect to reduced monomer units on the PAN film surface. The rate of this phase corresponds to typical values of electrical current observed with PAN electrodes. Later, the kinetics changes into a diffusion-controlled process. The H+ permeability of the PAN film increases with an increase of the intrinsic oxidation state of the films. It was found that each reduced monomer unit in the PAN film can provide more than one electron. The mechanism of the two-stage kinetics is proposed and the equilibrium constants of emeraldine base protonation, Fe3+ adsorption and also the constants of electron transfer from protonated emeraldine to absorbed Fe3+ are estimated. (C) 2000 Elsevier Science B.V. All rights reserved.