ULTRATHIN SELF-ASSEMBLED POLYMER-FILMS ON SOLID-SURFACES .4. ELECTROCHEMICAL ANALYSIS OF FILM MICROSTRUCTURE ON GOLD ELECTRODES

Bound monolayer films of alkyldisulfide-grafted polyacrylates on gold electrodes were studied via electrochemical cyclic voltammetric method s. Ferricyanide, ruthenium hexamine, and alkyl viologen redox probes i n aqueous electrolyte were used to reveal the response of coated ultra thin films on electrodes to different probe molecules, film defects, a nd surface coverages. Surface microstructure of these films assembled on gold electrodes probed by cyclic voltammetry (CV) produced electron -transfer blocking efficiencies very dependent upon the redox probe ut ilized. Current-voltage profiles using ferricyanide indicated efficien t blocking of the electrochemistry mediated by aqueous redox probes wh ile films probed with ruthenium hexamine exhibited a leakier structure . Poor redox blocking efficiencies were observed on these same coated electrodes using methyl and alkyl viologen redox probes, exhibiting a current spike corresponding to surface adsorption of reduced viologen species, indicating incomplete electrode surface coverage by the polym er monolayer films. Morphological changes in coated films upon exposur e to organic solvent at various temperatures were also examined using CV analysis. Despite structural defects resulting from relatively loos e-packed polymer film architecture, ellipsometric and X-ray photoelect ron spectroscopy measurements indicate that a molecular or microscopic rearrangement of film components, rather than partial removal of coat ed films, is responsible for the observed changes in barrier propertie s.