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Les propriétés d’auto organisation de tensioactifs ainsi que celles de la chimie de la silice ont permis de préparer des matériaux mésoporeux organisés selon une symétrie hexagonale, cubique ou lamellaire dont la taille des pores varie de 2 à plus de 10 nm. Ils sont depuis quelques années le centre d’intérêt d’universitaires et d’industriels qui développent des recherches fondamentales et appliquées. La compréhension globale des mécanismes de synthèse et la maîtrise des propriétés structurales et texturales des matériaux mésoporeux sont nécessaires pour envisager leur utilisation dans un quelconque procédé industriel. Dans ce cadre, nous avons étudié les relations entre les propriétés physico-chimiques d’un tensioactif fluoré C7F15C2H4(OC2H4)8OH et les caractéristiques des silices mésoporeuses. Malgré l’existence d’une phase micellaire, les canaux poreux des matériaux obtenus avec ces solutions micellaires ne sont pas organisés. En revanche, l’addition de la perfluorodécaline provoque une structuration du matériau selon une symétrie hexagonale. L’utilisation de divers fluorocarbures, ayant des structures moléculaires différentes, montre que le phénomène est associé au déplacement de la courbe de point de trouble vers les hautes températures. De plus, il a été montre que la préparation de matériaux à porosité hiérarchisée à partir d'émulsions de type huile dans eau est corrélée à la température d’inversion de phase du système eau/huile/tensioactif. Enfin, les matériaux mésoporeux ont été mis à profit pour immobiliser des enzymes et les résultats montrent que les lipases physisorbées conservent une activité catalytique. / The self-assembly properties of surfactants and those of silica chemistry have led to the preparation of ordered mesoporous materials with hexagonal, cubic or lamellar symmetry and with pore sizes varying from 2 to more than 10 nm. Recently, they have aroused of great deal of interest to academics and industrialists for the development of fundamental and applied research. However, their use in any industrial process needs a careful consideration of the total comprehension of the synthesis mechanism as well as the control of their structural and textural properties. In this work, the relation between the physicochemical properties of a fluorinated surfactant, C7F15C2H4(OC2H4)8OH, and the characteristics of mesoporous silica was investigated. In spite of the existence of a micellar phase, only wormlike mesoporous materials were obtained. On the other hand, the addition of the perfluorodecalin led to the organisation of the channels according to a hexagonal symmetry. The use of various fluorocarbons of different molecular structures evidenced that this phenomenon is associated to the shift of the cloud point curve towards higher temperatures. Hierarchically porous silica were also prepared from oil-in-water emulsions and their characteristics were correlated to the phase inversion temperature of the surfactant/water/oil system. Finally, the mesoporous materials were used as hosts for the physisorption of enzymes and the results showed that the catalytic activity of the immobilised lipases is preserved.

In binary systems, surfactant molecules can self-assemble into a large variety of structures depending on their chemical structure, concentration and temperature. The properties and stability of the phases, their coexistence regions and the formation of metastable structures is of great importance not only for fundamental understanding, but also for applications in many fields including industry and medicine. This thesis presents studies of the equilibrium and non-equilibrium behaviour of two widely used surfactant systems. The understanding of the equilibrium behaviour of an aqueous surfactant system is often incomplete or partly incorrect, which is caused by experimental difficulties, long equilibration times and the occurrence of long-lived metastable states. By applying a set of complementary techniques and recording changes on different length scales, the equilibrium phase diagram of the surfactant didodecyldimethylammonium bromide (DDAB) in water has been studied and amended. Differential scanning calorimetry has been used to obtain thermodynamic parameters. The structure of phases and biphasic regions have been characterised by small angle X-ray scattering and microscopy, while the conformational properties of the surfactant molecules have been investigated using Raman spectroscopy combined with computational methods. The effects of impurities have been studied using analytical techniques and a sufficient purity of the samples could be ensured. As a result of the studies, a new crystalline phase which exists at temperatures below 16°C was found. This phase replaces the frozen lamellar phase (Lβ) in the previously reported phase diagram. The Lβ phase has been found to be a long-lived metastable phase. The amended phase diagram has been tested by studying phase transitions along isoplethal and isothermal paths. All experimental results could be explained in terms of the new phase diagram. The study of phase transition along isoplethal paths focused on the transition between the new crystalline phase (XWn) coexisting with a dilute monomer solution (W) and the lamellar phase (Lα). This transition was (except for a single composition DDAB≈3% DDAB) a non-isothermal transition involving the phase sequence: XWn +W → XWn + Lα → Lα upon heating and Lα → overcooled Lα → XWn +W upon cooling. The structural changes within the phases and their relative ratios could be characterised using small angle X-ray scattering, microscopy and Raman spectroscopy. During the dissolution of lamellar phases along an isothermal path, multilamellar wormlike interface instabilities (so called myelins) were found to grow from the lamellar/water interface into the water. The growth of these myelins as well as changes in the lamellar phase have been investigated using optical microscopy and direct observation. This has provided detailed quantitative information on the dynamics of myelin growth and the effect of the initial structure of the lamellar phase on the myelin growth. The dependence of the growing rate on surfactant concentration could be explained in terms of a previously reported model in which the osmotic pressure was stated to be the driving force for the myelin kinetics. It has been found that for lamellar phases in coexistence with a sufficient amount of crystals, the myelin growth could be suppressed. Preliminary measurements of a tertiary system, where the pure lamellar phase of DDAB was mixed with a crystalline phase formed by dioctadecyldimethylammonium bromide (DODAB), a DDAB analogue, were carried out. The myelin growth has also been studied for a second system, the non-ionic surfactant triethylene glycol monododecyl ether (C12E3), known for its formation of myelins of great stability. The optical methods were extended to confocal microscopy, resulting in a 3D image of the myelin formation, providing detailed quantitative information on myelin growth as well as on myelin size.

The alveoli of mammalian lungs are covered in a thin lipid film referred to as pulmonary surfactant. The primary purpose of pulmonary surfactant is to reduce the surface tension of the air/liquid interface allowing breathing with minimal effort required. We investigated the effect of addition of cholesterol and amyloid-β peptide on structure and function of Bovine Lung Extract Surfactant (BLES) and model lipid films. In our first experiment, we have demonstrated the effect of amyloid-β and cholesterol on lipid films of DPPC, DPPC-DOPG and BLES. We saw that cholesterol inhibits multilayer formation in all monolayers. Amyloid-β increases multilayer formation in DPPC and DPPC-DOPG, but reduced multilayer formation in BLES. When cholesterol and amyloid-β is added to BLES, 1% amyloid-β is inconsequential, whereas 10% amyloid-β allows BLES to regain some of its surfactant function. In our second experiment, we observed that for bothanionic DOPG and cationic DOTAP films which are in the fluid phase, amyloid-β interacts with the bilayer much quicker than in zwitterionic DPPC which is in the gel phase. Approaching 24 hours, we see small fibrils form on the bilayer, but these fibrils are considerably smaller than those formed when amyloid-β is incubated in solution. For fluid phase bilayer membrane, disruption is also observed. We investigated the effect of addition of cholesterol and amyloid-β peptide on structure and function of Bovine Lung Extract Surfactant (pulmonary surfactant BLES) and model lipid films. In our first experiment, we have demonstrated the effect of amyloid-β and cholesterol on lipid films of DPPC, DPPC-DOPG and BLES. We saw that cholesterol inhibits multilayer formation in all monolayers. Amyloid-β increases multilayer formation in DPPC and DPPC-DOPG, but reduced multilayer formation in BLES. When cholesterol and amyloid-β is added to BLES, 1% amyloid-β is in consequential, whereas 10% amyloid-β allows BLES to regain some of its surfactant function. In our second experiment, we observed that in anionic DOPG films, amyloid-β inserts into the bilayer much quicker than in zwitterionic DPPC. Approaching 24 hours, we see small fibrils form in the bilayer, but these fibrils are considerably smaller than those formed when amyloid-β is incubated in solution.

The alveoli of mammalian lungs are covered in a thin lipid film referred to as pulmonary surfactant. The primary purpose of pulmonary surfactant is to reduce the surface tension of the air/liquid interface allowing breathing with minimal effort required. We investigated the effect of addition of cholesterol and amyloid-β peptide on structure and function of Bovine Lung Extract Surfactant (BLES) and model lipid films. In our first experiment, we have demonstrated the effect of amyloid-β and cholesterol on lipid films of DPPC, DPPC-DOPG and BLES. We saw that cholesterol inhibits multilayer formation in all monolayers. Amyloid-β increases multilayer formation in DPPC and DPPC-DOPG, but reduced multilayer formation in BLES. When cholesterol and amyloid-β is added to BLES, 1% amyloid-β is inconsequential, whereas 10% amyloid-β allows BLES to regain some of its surfactant function. In our second experiment, we observed that for bothanionic DOPG and cationic DOTAP films which are in the fluid phase, amyloid-β interacts with the bilayer much quicker than in zwitterionic DPPC which is in the gel phase. Approaching 24 hours, we see small fibrils form on the bilayer, but these fibrils are considerably smaller than those formed when amyloid-β is incubated in solution. For fluid phase bilayer membrane, disruption is also observed. We investigated the effect of addition of cholesterol and amyloid-β peptide on structure and function of Bovine Lung Extract Surfactant (pulmonary surfactant BLES) and model lipid films. In our first experiment, we have demonstrated the effect of amyloid-β and cholesterol on lipid films of DPPC, DPPC-DOPG and BLES. We saw that cholesterol inhibits multilayer formation in all monolayers. Amyloid-β increases multilayer formation in DPPC and DPPC-DOPG, but reduced multilayer formation in BLES. When cholesterol and amyloid-β is added to BLES, 1% amyloid-β is in consequential, whereas 10% amyloid-β allows BLES to regain some of its surfactant function. In our second experiment, we observed that in anionic DOPG films, amyloid-β inserts into the bilayer much quicker than in zwitterionic DPPC. Approaching 24 hours, we see small fibrils form in the bilayer, but these fibrils are considerably smaller than those formed when amyloid-β is incubated in solution.

The first goal of this research was to develop and experimentally test new and improved chemical formulations for enhanced oil recovery using a new class of branched large-hydrophobe alkoxy carboxylate surfactants mixed with novel co-surfactants and co-solvents to both lower IFT and alter wettability at high temperatures and high salinities. These novel alkoxy carboxylate surfactants with large branched hydrophobes were tested and found to show excellent performance in corefloods over a wide range of reservoir conditions up to at least 120°C. The number of PO and EO groups in these new surfactants were optimized for a wide variety of oils over a broad range of salinity, hardness and temperature and mixed with various co-surfactants and co-solvents to develop high-performance formulations based on the microemulsion phase behavior. Both ultra-low IFT and clear aqueous solutions at optimum salinity were obtained for both active and inactive oils and both light and medium gravity oils over a wide range of temperatures. Both sandstone and carbonate corefloods using these carboxylate surfactants showed excellent performance at high temperature, high hardness and high salinity as indicated by high oil recovery, low pressure gradients and low surfactant retention. The advent of such a new class of cost-effective surfactants significantly broadens the potential application of chemical enhanced oil recovery processes using surfactants under harsh reservoir conditions. The second goal of this research was to evaluate the effect of buoyancy on oil recovery from cores using ultra-low IFT surfactant formulations under conditions where the use of polymer for mobility control is either difficult or unnecessary, determine the conditions that are favorable for a gravity-stable surfactant flood, and further improve the performance of gravity-stable surfactant floods by optimizing the microemulsion properties, especially its viscosity. The microemulsion viscosity can be varied by adjusting the structure of the surfactants and co-solvents and their concentrations. Predictions made using classical stability theory applied to surfactant flooding experiments were determined to be inaccurate because such theory does not take into account the microemulsion phase that forms in-situ when surfactant mixes with the oil. The modification of the classical theory to account for the effect of the microemulsion on the critical velocity for a stable displacement is one of the major contributions of this research. New experiments were done to test the modified theory and it was found to be in good agreement with these experiments. Furthermore, a new method to increase the stable velocity by optimizing the microemulsion viscosity was proposed and validated by a series of coreflood experiments designed and conducted for that specific purpose. / text

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