STUDY OF THE GRAFTING AND OF THE ELECTROCHEMICAL POLYMERIZATION OF ACRYLIC-MONOMERS ON A METALLIC SURFACE BY IMPEDANCE SPECTROSCOPY

Under cathodic polarization in aprotic media some vinylic monomers like acrylonitrile and methacrylonitrile can be polymerized and strongly bound to a metallic surface (nickel for instance). The bonding of polymer films on metallic electrodes has been studied by electrochemical impedance spectroscopy combined with classical electrochemical methods such as chronoamperometry and linear sweep voltammetry. The growth of the polymer on the surface introduces a change in the double layer capacitance on the metal which can be measured by impedance spectroscopy when the polymer is swelled by the electrolytic solution. The modification of the double layer capacitance is related to the part of the surface occupied by the bonds between the polymer and the metal (grafting ratio). This ratio was found to be dependent on the surface preparation mode and on the concentration of the monomer in the electrolytic solution used for the polymerization process. This result makes clear the differences observed in the thickness and in the morphology of the polymers obtained when using various monomer concentration and different treatments of the metallic surface. On the other hand the impedance results allow us to give a correct interpretation of the usual electrochemical characteristics (current-potential curves and current-time curves) registered during the electropolymerization process in various conditions.