Bucureºti) ♦ 61♦ Nr

The preparations and characterization of polypyrrole -polyethylene glycol (PPy-PEG) In the present paper, we report the electrochemical preparation and characterization in buffer solution of both PPy films and PPy composite films with PEG added as insulating polymer. Several techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM) have been used to study the behaviour of the composite films deposited on Ti. The attention has been focused on the role played by the PEG presence in the film on the adherence and electrochemical stability of polymeric films. Experimental part Materials The metallic substrates were represented by commercially pure Ti discs of 1 mm thickness and 10 mm diameter (99.6% purity, Goodfellow Cambridge Ltd., UK). The deposition surfaces of test specimens were polished with SiC paper to grade 4000. Before deposition, the discs were cleaned in acetone and rinsed well with distilled water. The electrochemical deposition of PPy was performed in aqueous solution of 0.2 mol·L -1 Py and 0.2 mol·L -1 oxalic acid. For composite PPy-PEG films electropolymerization of pyrrole was performed in the presence of 5% PEG (400 molecular weight) in the same aqueous solution. Pyrrole monomer was purchased from Aldrich, and stored in the dark at 4 o C before use. All solutions were prepared using ultra pure deionised Milli-Q water. The composition of buffer solution used for characterization was: NaCl 8.74 g/L; NaHCO 3 0.35 g/L; Na 2 HPO 4 ·12H 2 O 0.06 g/L; NaH 2 PO 4 0.06 g/L; Methods The electrochemical data were recorded at room temperature using a conventional cell with three electrodes: a Ti working electrode, a platinum counterelectrode and an Ag/AgCl, KCl reference electrode, all connected to Autolab PGSTAT 302 N potentiostat with general-purpose electrochemical system software GPES 4.9. Potentiodynamic polymerisation was used for the synthesis of the polypyrrolle film on the electrode surface. Cyclic voltammetr y, electrochemical impedance spectroscopy were used as electrochemical characterisation techniques. The electrochemical impedance spectroscopy data were obtained with the Autolab frequency response analyzer FRA 4.9 and fitted with NOVA 1.4 software. The surface topography of polypyrrole films was studied with Atomic Force Microscopy (AFM) in non contact mode, at room temperature with a scan rate of 7 μm/s. Results and discussion Electrochemical deposition of polypyrrole -polyethylene glycol coatings on Ti electrode PPy and PPy-PEG films were deposited electrochemically by potentiodynamic polymerization in 0.2 M oxalic acid aqueous solution in the presence of 0.2 M pyrrole