F. Sun et al., ULTRATHIN SELF-ASSEMBLED POLYMER-FILMS ON SOLID-SURFACES .4. ELECTROCHEMICAL ANALYSIS OF FILM MICROSTRUCTURE ON GOLD ELECTRODES, Colloids and surfaces. A, Physicochemical and engineering aspects, 93, 1994, pp. 191-200
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.