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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.

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Gemini surfactants are an intriguing class of surface active agents that are comprised of two surfactant monomers chemically linked at or near the headgroups by a rigid or flexible spacer. In comparison to their corresponding monomer counterparts, gemini surfactants are more efficient at reducing surface tension, have better wetting properties, and typically have critical micelle concentration values that are one to two orders of magnitude lower. These intriguing properties characteristic of gemini surfactants make them of special interest for pharmaceutical applications. Within this work, two different projects were carried out to assess the pharmaceutical applications of gemini surfactants. The aim of the first project was to assess the applications of gemini surfactants as transfection agents for non-viral gene delivery by evaluating the physical stability characteristics of gemini surfactant-based lipoplex systems. Prior to this investigation, an evaluation of the interaction properties between gemini surfactants and DNA, and between gemini surfactants and the neutral helper lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine was carried out using a combination of isothermal titration calorimetry, particle size, zeta potential and surface tension measurements. Following these evaluations, the physical stability of the gemini surfactant-based DNA delivery systems was assessed by examining the particle size distribution and membrane integrity characteristics of the lipoplexes. The results from this analysis revealed that the physical stability of these systems is limited by the membrane integrity characteristics of the lipoplex structure. The second project carried out was an evaluation of the interactions between gemini surfactants and a series of Tween surfactants commonly found in pharmaceutical formulations. The results from this analysis were analyzed using Clint’s, Rubingh’s, Motomura’s and Maeda’s theories for mixed micelle formation, where it was observed that there is a general synergistic mixing interaction present between gemini and Tween surfactants. The strength of synergism was found to be dependent upon the chain length and saturation of the Tween alkyl tail.

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Reproduction de : Thèse de doctorat : Génie chimique et environnement : Toulouse, INPT : 2008. / Titre provenant de l'écran-titre. Bibliogr. 801 réf.

Viscoelastic surfactant (VES) fluids are preferred for many applications in the oil industry. Their viscoelastic behavior is due to the overlap and entanglement of very long wormlike micelles. The growth of these wormlike micelles depends on the charge of the head group, salt concentration, temperature, and the presence of other interacting components. The problem with these fluids is that they are expensive and used at temperatures less than 200°F. The viscoelasticity of nanoparticle-networked VES fluid systems were analyzed in an HP/HT viscometer. A series of rheology experiments have been performed by using 2-4 vol% amidoamine oxide surfactant in 13 to 14.2 ppg CaBr2 brines and 10.8 to 11.6 ppg CaCl2 brines at different temperatures up to 275°F and a shear rate of 10 s-1. The nanoparticles evaluated were MgO and ZnO at 6 pptg concentration. In addition, the effect of different nanoparticle concentrations (0.5 to 8 pptg) and micron size particles on the viscosity of VES fluid was investigated. The oscillatory shear rate sweep (100 to 1 s-1) was performed from 100 to 250°F. The effect of fish oil as an internal breaker on the viscosity of VES micelles was examined. This study showed that the addition of nanoparticles improved the thermal stability of VES micellar structures in CaBr2 and CaCl2 brines up to 275°F and showed an improved viscosity yield at different shear rates. Micro- and nanoparticles have potential to improve the viscosity of VES fluids. Lab tests show that for VES micellar systems without nanoparticles, the dominant factor is the storage modulus but when nanoparticles are added to the system at 275°F the loss modulus becomes the dominant factor. These positive effects of nanoparticles on VES fluid characteristics suggest that these particles can reduce treatment cost and will exceed temperature range to 275°F. With this work, we hope to have better understanding of nanoparticle/viscoelastic surfactant interaction.

Soil remediation requires technologies to restore contaminated soil to a state that is environmentally acceptable. In most cases, while the soil can be remediated the contaminant itself cannot be reclaimed. Soil washing involves cleaning contaminated soil with a wash solution, generally an aqueous solution of a surfactant. It was proposed that using switchable surfactants for washing oil-contaminated soil will not only help remove the oil from soil, but also aid in the recovery of the oil contaminant from the wash mixture. Six surfactants were evaluated for their ability to wash Ottawa Sand artificially contaminated with North Sea crude oil. A water wash solution was used as a control. Two commercial surfactants, sodium dodecyl sulfate (SDS) and Triton X-100, and four switchable surfactants, N'-octyl-N,N-dimethylamidine (C8), sodium octyl 4-hydroxy-3-nitrobenzoate (SAS1), sodium 4-(octyoxy) benzoate (SAS2) and sodium laurate (SAS3) were studied. The surfactants were assessed based on their ability to remove oil from the sand and their ability to separate the crude oil from the wash mixture after CO2 treatment. Oil removal from sand was determined by gravimetric analysis. Oil content in the wash mixture was determined using Solid Phase Extraction and gravimetric analysis. It was determined that switchable surfactants are able to remove North Sea crude oil from sand as well or better than the commercial surfactants and have the added feature of oil separation and recovery from the wash mixture after CO2 treatment. / Thesis (Master, Chemistry) -- Queen's University, 2011-02-16 17:10:16.997