Structural Studies of Surfactants at Interfaces

Abstract

This thesis consists of a collection of studies on surfactant adsorption at different interfaces. Particularly, this dissertation focuses on adsorption processes occurring at buried interfaces (solid-liquid and liquid-liquid). Because of complexity in the sample environment, the study of buried interfaces is experimentally challenging. Neutron reflectivity enables the study of adsorption processes at interfaces at atomic length scale. Furthermore, neutrons can be transmitted through solid substrates, permitting the analysis of buried interfaces. The technique was used to describe adsorption processes both qualitatively and quantitatively, delivering information regarding structure of adsorbed layers and adsorbed amount. Different investigations were carried out during the PhD and the results are grouped into two main sections. Investigations at the solid-liquid interface are presented in the first section. Chapter 3 provides an example of structural study of complex multi-layers at the silicon-water interface; a surfactant adsorption study at the technologically relevant metal-oil interface is presented in Chapter 4. The second section discusses a series of neutron reflectivity experiments at the important oil-water interface. The structural study of a series of non-ionic dodecanol ethoxylate surfactants is discussed in Chapter 6. The structure of a lipid monolayer as model for a biological membrane is reported in Chapter 7. Chapter 8 is a comparative study of fatty acid-alkylated azacrown ether co-adsorption at the air-water and oil-water interface. These mixtures are used for metal ion extraction processes. This was the first analysis of a surfactant mixture at the oil-water interface using neutron reflectivity. Some of the studies reported here are the first of their kind and the advances affect different technologically and biologically relevant areas. As a result of this PhD project a number of follow-up studies have been planned and several neutron reflectivity experiments will be performed in the future to further explore these interesting areas of science.