No description available.

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.

The dissolution of quantum sized CdS and MnO2 particles in water was conducted using 20 kHz ultrasound. CdS particles were found to dissolve chemically via an oxidation process while MnO2 particles dissolved via a reductive process. It was found that the dissolution of the colloids could be controlled via the addition of surface active chemicals to solution and by varying the saturation gas type. In the presence of Na2S or propan-2-ol and argon gas, the dissolution of CdS was inhibited, whereas the addition of alcohols (methanol, ethanol, propan-2-ol, butan-1-ol and pentan-1-ol) to the MnO2 system led to an increase in the amount of dissolution for a given time of sonication. This increase in dissolution was found to be dependent on the ability of the surface active radical scavenger to accumulate around the bubble interface during the cavitation process. Eventually, at higher alcohol concentration there was a plateau or a limiting value reached for the efficiency of colloid dissolution which was common for each alcohol. (For complete abstract open document)