Fluorescence imaging studies of the electrochemical adsorption/desorption of octadecanol

A confocal fluorescence imaging study of the potential-induced adsorption/d esorption of octadecanol onto/from a Au(111) electrode is presented. Octade canol is known to adsorb onto the electrode surface from the air-water inte rface, 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 cha racterization of the influence of potential on the physical characteristics of the molecules near or on the electrode surface. Images at potentials ch aracteristic of the adsorption and desorption process as well as intermedia te potentials were measured. The observation of fluorescence from surfactan t aggregates at the desorption potential indicated that these aggregates we re separated from the electrode surface. Readsorption of the desorbed surfa ctants was observed revealed by the gradual disappearance of fluorescence d ue to quenching by the gold surface. The influence of the initial depositio n conditions was also investigated. Significant differences were observed i n the overall intensity, the size, and structure of the desorbed surfactant s with the amount of surfactant deposited onto the electrode surface. J-agg regates were observed for the higher coverage layers indicating dye aggrega tion. At intermediate potentials between the adsorption and desorption limi ts, evidence of adsorbed intermediate structures was observed. The desorbed surfactants were observed to exist as a diffuse collection away from the e lectrode surface. These are preliminary results, and further work is planne d for measuring the size distribution of aggregates and its dependence on p otential.