Ljerka Duić

Polyaniline as an electrocatalytic material

Abstract The catalytic influence of polyaniline (PANI) film, prepared from sulphuric and perchloric acid solutions, on hydroquinone/benzoquinone ( HQ BQ ) and Fe 2+ 3+ reactions has been investigated. The effect of the PANI layer thickness on redox reactions has been established, as well as different kinetics depending on the counter-ion incorporated. The location of the reactions taking place is discussed. Evidence is given for metal-like behaviour of PANI at potentials of emeraldine existence and redox-polymer behaviour at potentials of pemigraniline existence.

Polymer-dimer distribution in the electrochemical synthesis of polyaniline

The distribution of major products associated with the process of polyaniline (PANI) synthesis is discussed. On the basis of the results obtained in the cyclovoltammetric (cv) and constant potential (cp) synthesis the dependence of that distribution upon monomer concentration, switching potential (Eλ) and potential of synthesis, Esynth, are discussed, the corresponding reaction scheme is given and terms for the reaction rates derived. The conditions governing the polymer-dimer distribution are formulated. The origin of the middle peak, appearing during the PANI synthesis, is discussed in the light of the specific experimental conditions, and species corresponding to it are identified. A reaction scheme for the hydrolysis pathway of dimer is confirmed.

Counter-ion and pH effect on the electrochemical synthesis of polyaniline

Abstract The effect of different electrolytes at various pH values on the electropolymerization of aniline from aqueous solutions has been studied. It has been found that polyaniline can be synthesized within the whole pH range investigated, provided that the proper counter-ion is present. Distinct regions of different pH effect on aniline polymerization have been identified and the corresponding reaction mechanisms suggested. It was also found that polyaniline synthesized in the solutions having high pH values, when transferred to acidic solutions, switched from a non-conductive to a conductive state, giving voltammograms and FTIR spectra characteristic of PANI synthesized in acidic media.

The influence of counter-ions on nucleation and growth of electrochemically synthesized polyaniline film

The initial stages of polyaniline (PANI) film growth are investigated by a potentiostatic technique. The obtained I-t transients exhibit current maxima which are analyzed for the nucleation type. The evidence is given on two different stages of the nucleation process. It is established that the first stage of growth is a formation of a compact PANI layer which is followed by an additional nucleation process. For that nucleation process it is found that at lower concentrations of aniline monomer 3D progressive nucleation takes place, and with the increasing monomer concentration in perchloric acid solutions 3D instantaneous nucleation prevails. At later stages 1D growth takes place resulting in chain branching. The possibility to observe current maxima, indicating the particular nucleation process, depends on monomer concentration, on the potential of synthesis, and on the counter-ion present, ie on the rate of PANI polymerization. It is shown that clusters resulting from the nucleation process form different shapes depending on the counter-ion present.

Electrochemical reduction of p-nitrosodiphenylamine in a cationic micellar system

Abstract The electroreduction of p-nitrosodiphenylamine (p-NDPA) in an alkaline aqueous solution containing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was investigated by polarography, cyclic and rotating disc voltammetry. It was found that the reduction of p-NDPA in cationic micellar systems takes place by the ECE mechanism, and, compared to the reduction of the same compound in a homogeneous water solution, has a somewhat lower rate of the overall electrode reaction. The lower reaction rate of p-NDPA reduction in micellar medium is probably due to three main factors: solubilization of p-NDPA in CTAB micelles, adsorption of monomeric surfactant species at the electrode surface and a lower rate of the base catalyzed dehydration reaction (C-step) in the micellar system.