Preparation and characterization of alkanethiolate self -assembled monolayers onto gold from environmentally benign solvent

This dissertation focuses on the preparation of high-quality n-alkanethiolate self-assembled monolayers (SAMs) onto gold from environmentally benign solvents, including aqueous micellar solutions and supercritical carbon dioxide, instead of traditional organic solvents.;The first part of this dissertation details the micelle-assisted formation of SAMs in aqueous solutions. Micelles formed from nonionic and cationic surfactants function as vehicles to solubilize, deliver, and release water-insoluble alkanethiol molecules to gold surfaces to form SAMs in aqueous solutions. The kinetics of SAM formation depends on the micelle structure, surfactant charge, the concentrations of added surfactant and solubilized alkanethiol, and the chain lengths of surfactant and alkanethiol. The nature of the dependence of the kinetic rate on these variables provides molecular-level insight on the delivery and release processes. These micelle-assisted SAMs exhibit greater overall chain densities and are more electrochemically blocking than those formed from traditional organic solvents such as ethanol and isooctane. The greater overall chain density for the water-borne SAMs is attributed to hydrophobic interactions between alkyl chains during assembly process which enable the formation of films with larger domains and fewer defects. These water-borne SAMs also exhibit a more stable structure than that of solvent-borne SAMs when exposed to blank solvents. The combination of these results demonstrates that the selection of solvents that exhibit weaker interactions with both the adsorbates and the growing film can produce SAMs with superior structures and properties.;The second part of this dissertation describes the formation of n-alkanethiolate SAMs onto gold in liquid and supercritical carbon dioxide. The results of this study show for the first time that carbon dioxide can be used to form highly crystalline alkanethiol-based SAMs and that pressure as well as exposure time can be used to affect the structural and barrier properties of the monolayer film. In addition, we report the use of ethanol-supercritical carbon dioxide mixtures as solvents in the formation of SAMs on gold. The ability to control the defect density within the SAM by simply altering the ethanol-carbon dioxide solvent composition represents a straightforward and environmentally friendly strategy to tune the properties of these molecular films.