Development and application electrochemical and spectrophotometric methods based upon AC potential modulation for characterization of hybrid bilayer membranes and electroactive self -assembled monolayers supported on gold electrodes

Applications of the electrochemical method, AC Voltammetry (ACV), and its modifications based upon monitoring ac current as a function of ac potential modulation are described. The first chapter involves investigating the effect of a short peptide, melittin, on both hybrid bilayer membrane (HBM) dielectric properties and HBM resistance to heterogeneous electron transfer. These effects are discussed in terms of three possible mechanisms by which melittin may affect HBMs. In the second chapter, a modification of ACV, second harmonic ACV, is considered. A data processing method is suggested to analyze data collected at high perturbation frequencies at which the effect of uncompensated resistance cannot be neglected. In the third chapter, application of the spectroelectrochemical modification of ACV, Electrochemically Modulated Reflectance ACV, is discussed. The electromodulation reflectance coefficient, a ratio of ac electroreflectance to both DC electroreflectance and ac interfacial potential, is shown to be the most useful quantity to represent ac electroreflectance data. The same kinetic information on the surface faradaic reactions is available from electrochemical and spectroelectrochemical data. In the final chapter, ACV is applied to determine the rate of electron transfer kinetics for a redox couple attached via short alkanethiols (C5, C7, C 10) to a gold electrode. The semilog plot of standard rate constant vs. the number of methylene units remains linear down to the shortest used chain length (C5)

Electrical properties of UHMWPE/graphite nanoplates composites obtained by in-situ polymerization method

There are described nanocomposites based on ultra high molecular weight polyethylene and graphite nanoplates prepared by in-situ polymerization method. It is carried out a comprehensive study of electric properties of these composites, including direct current (dc) and alternating current (ac) properties. There is explored dependence of the conductivity and dielectric permeability on filler concentration, temperature, deformation and frequency of electric field. These relationships are compared with those for composites based on other carbon fillers including both nanoscale (carbon nanotubes, carbon black) and micron-sized (graphite, schungite) fillers. More specific electrical properties of investigated materials such as lower percolation threshold and higher dielectric permittivity compared to those for composites based on other carbon fillers are attributed to the plate-like shape of graphite nanoplates. These materials are distinguished also by their high electrical stability against temperature and deformation. Therefore, it makes graphite nanoplates the most preferable conductive filler for some practical applications. Some possible application areas for UHMWPE/graphite nanoplates nanocomposites will be also discussed

Influence of composition, bonding characteristics and microstructure on the electrochemical and optical stability of AlOxNy thin films

Thin films of AlOxNy were deposited by magnetron sputtering in a wide composition range. Different structures and morphologies were observed, depending on the composition and bonding states, which opened the possibility to tailor the properties of this oxynitride system between those of pure Al and those of nitride and oxide films. In a wide range of stoichiometries, one can report the formation of nanocomposite porous films, where Al nanoparticles are dispersed in an amorphous matrix of AlOxNy. The electrochemical behaviour of the films was studied in isotonic NaCl solution. It was observed that the pitting 2 potential characteristic of aluminium disappears with the incorporation of oxygen and nitrogen in the films, being replaced by a smooth current increase. Electrochemical impedance spectroscopy performed during 35 days showed that the corrosion resistance of the films steadily increases. The unusual optical reflectance profile of some films is maintained after immersion for several months.Fundação para a Ciência e a TecnologiaPrograma Pessoa 2010/2011, Cooperação Portugal/França, Proc.º 441.00, Project“COLOURCLUSTER”