Fluorescence imaging studies of the electrochemical adsorption/desorption of octadecanol

A confocal fluorescence imaging study of the potential-induced adsorption/desorption of octadecanol onto/from a Au(111) electrode is presented. Octadecanol is known to adsorb onto the electrode surface from the air-water interface, and at a sufficiently negative potential, the surfactant is desorbed. The carbocyanine dye, DiIC(18)(5) was mixed with the octadecanol at 3 mol % concentration allowed the use of fluorescence imaging techniques for characterization of the influence of potential on the physical characteristics of the molecules near or on the electrode surface. Images at potentials characteristic of the adsorption and desorption process as well as intermediate potentials were measured. The observation of fluorescence from surfactant aggregates at the desorption potential indicated that these aggregates were separated from the electrode surface. Readsorption of the desorbed surfactants was observed revealed by the gradual disappearance of fluorescence due to quenching by the gold surface. The influence of the initial deposition conditions was also investigated. Significant differences were observed in the overall intensity, the size, and structure of the desorbed surfactants with the amount of surfactant deposited onto the electrode surface. J-aggregates were observed for the higher coverage layers indicating dye aggregation. At intermediate potentials between the adsorption and desorption limits, evidence of adsorbed intermediate structures was observed. The desorbed surfactants were observed to exist as a diffuse collection away from the electrode surface. These are preliminary results, and further work is planned for measuring the size distribution of aggregates and its dependence on potential.