| The molecular level organization of the surfactants at solid-liquid interfaces has been investigated. Specifically, the effect of the surface properties such as hydrophobicity, crystallinity, and surface charge density and the effect of surfactant structural properties such as surfactant type, and headgroup size, on the formation of the surface micelle structures have been studied.;Primarily "soft contact" atomic force microscope imaging has been used to visualize the nanometer scale organization of surface micelle structures at selected surfaces. In addition to AFM imaging, surface micelle structures were examined using other supporting techniques such as FTIR/IRS, contact angle, and interaction force measurements to further describe the selected systems. At hydrophobic surfaces such as graphite and glassy carbon, the AFM images revealed self-assembled ordered arrays of remarkable structures, which were characterized to be hemimicelles. In contrast, for the adsorption of oppositely charged surfactants at the hydrophilic surfaces such as mica, silica, and alumina, full micelles were observed at the hydrophilic surfaces mica, silica, and alumina.;The templating effect of the crystalline graphite surface superceded all other molecular contributions, leading to the formation of highly ordered hemicylindrical structures for a variety of surfactants, with dimensions in the range of 5-6 nm. In comparison, at the amorphous glassy carbon surface only randomly ordered hemispherical structures are formed, with similar dimensions of 5-6 nm. At the hydrophilic surfaces, however, a variety of structures ranging from wormy cylinders to spheres with dimensions around 5 to 6 nm have been observed, both at the crystalline mica and amorphous silica and alumina surfaces. The shape of the surface micelles at hydrophilic surfaces is greatly influenced by the surface charge density and the size of the headgroup.;It has been demonstrated for the first time that the surface micelles at the graphite surface can be modulated either physically by introducing some defects at the surface, or chemically through the addition of a cosurfactant. The changes seen with the addition of cosurfactant include longer adsorption kinetics and swollen micelles.;Theoretical equations have been developed for the evaluation of the van der Waals interaction force between hemicylinders, resembling the surface micelle structures at graphite surface. The values obtained for the size and separation of the hemicylinders through balancing the van der Waals force against the repulsive structural forces measured with AFM under high electrolyte concentrations compared very well with the dimensions obtained for the hemicylindrical surface micelles observed through AFM imaging. The values differed by less than 3% for different calculations. |
