Ulm, Univ. Diss., 2006.

Universiẗat-Gesamthochsch., Diss.--Paderborn, 1994.

No description available.

Lipid-detergent systems are interesting to study, as the two amphiphiles have very different spontaneous curvature, however readily form mixed micelles in solution. These micelles can be shorter cylindrical micelles or long worm-like micelles. For such a system the size of the micelles varies strongly with solute conditions, being dependent on the total amount of amphiphile in solution, as well as, the lipid to detergent ratio in the micelles. Although the broad phase behaviour of such systems has been studied and is relatively well understood, there are still many open questions remaining. Some of the questions that motivated the work presented are: how the length and composition of the micelles varies within the micellar region, and how the micelles grow? The biologically interesting system under study is lecithin and bile salt, where the equilibrium sizes were experimentally determined for different samples within the micellar region. A model, combining the length of the micelles, with the concentrations of lecithin and bile salt in the system is presented, and is used to calculate the composition of the micelles at equilibrium. The kinetics of the growth of the micelles after a pertubation causing a shift in the equilibrium size has not been studied in detail before. The kinetics of the system are studied using a stopped flow setup, which I specifically designed for neutron scattering experiments. The stopped flow setup allows for the measurement to start 200ms after the initial mixing of the two liquids, after dilution of a solution the micelles relax to a new longer length. The kinetics of this relaxation were studied as a function of the initial and final size of the micelles, as well as, the ionic strength of the solution. The micelles were found to grow through coalescence, where the rate of growth seems to be constant for different sizes of micelles and the time taken for the relaxation depends on the difference between the final and initial lengths of the micelles. The rate of growth is strongly influenced through changing the ionic strength of the solution, indicating the importance of an electrostatic barrier to the fusion of micelles.

Les solutions de micelles géantes sont utilisées dans plusieurs domaines industriels pour augmenter la viscosité d'une solution. Elles présentent un caractère viscoélastique bénéfique pour la fracturation hydraulique des roches pétrolifères car elles permettent de transporter le sable et de le maintenir en suspension. Cette thèse étudie les propriétés rhéologiques d’une solution commerciale destinée à la fracturation hydraulique. Cette solution est particulièrement délicate à caractériser car ses écoulements semblent être toujours instables. Nous avons mis au point une méthodologie permettant de la caractériser en régime laminaire, et avons montré que ce régime n’existe à température ambiante que pour des très faibles valeurs de taux de cisaillement. Habituellement, le comportement rhéologique dans le régime linéaire de ce type de solution est prédit par le modèle de Maxwell. Nous mettons en évidence que le comportement rhéologique de la solution étudiée ne correspond pas à ce modèle. Nous avons établi un modèle viscoélastique compatible avec les données expérimentales.Les instabilités d’écoulement de ces solutions sont d’origine élastique. Ce phénomène est largement étudié dans la littérature. Le comportement rhéologique dans le domaine non linéaire possède des caractéristiques propres à ces solutions. Notamment l’apparition d’un plateau de contrainte dans la courbe d’écoulement, précédé par une augmentation linéaire de la contrainte avec le cisaillement. Le début de ce plateau coïncide avec le déclenchement des instabilités, on parle de taux de cisaillement critique. La particularité de cette solution est la valeur faible de la contrainte plateau ainsi que du taux de cisaillement critique. Les valeurs observées sont cohérentes avec la valeur des paramètres rhéologiques obtenus dans les régimes d’écoulement laminaire. L’effet de certains paramètres physico-chimiques sur la rhéologie est également exploré. / Giant micelle solutions are used in several industrial domains to increase the viscosity of solution. Their viscoelastic characteristic is beneficial for hydraulic fracturing of oil rocks because these solutions are able to transport sand and to keep it in suspension. This thesis examines the rheological properties of a commercial solution, designed for hydraulic fracturing. This solution is particularly difficult to characterize because its flows seem to be always unstable. We have developed a methodology to characterize it in the laminar regime and we have shown that this regime exists at room temperature only for very low shear rate values. Usually, the rheological behavior of this type of solution, in the linear regime, is predicted by the Maxwell model. We prove that the rheological behavior of the studied solution doesn’t match this model. We have designed a viscoelastic model that is compatible with experimental data.The origin of flow instabilities of these solutions is elastic. This phenomenon is widely studied in the literature. The rheological behavior in the nonlinear regime has characteristics specific to these solutions. In particular, the appearance of a stress plateau in the flow curve, preceded by a linear increase of stress with shear. The beginning of this plateau match the onset of instabilities at a critical shear rate. The feature of this solution is the low value of the stress plateau as well as the critical shear rate value. They are consistent with the value of rheological parameters obtained in laminar flow regimes. The effect of some physico-chemical parameters on rheology is also explored.

No description available.

No description available.

In this dissertation, we studied two-phase microfluidics as a platform for the controlled synthesis of drug delivery polymeric nanoparticles (PNPs). The block copolymer we studied was poly(ε-caprolactone)-block-poly(ethylene oxide) (PCL-b-PEO). The anticancer drug we studied was paclitaxel (PAX). First, we explored microfluidic control of nanoparticle structure (size, morphology, and core crystallinity) on PCL-b-PEO PNPs without loaded PAX. We demonstrated the reproducible variability of PCL-b-PEO nanoparticle size and morphology. Microfluidic control of nanoparticle size and morphology was found to arise from the interplay of flow-induced particle coalescence and breakup. Next, we demonstrated the linear dependence of PCL core crystallization on flow-rate. We attributed this dependence of PCL core crystallization on flow-induced crystallization. We then used our microfluidic device to control PAX-loaded PNP structure and function (small molecule loading efficiency, diffusional release kinetics, and cytotoxicity). At low drug loading ratios (r < 0.1), we demonstrated reproducible variability of PAX-loaded PNP size and morphology. With increasing flow rate we were able to manufacture PNPs of high aggregation number. We were also able to reproducibly demonstrate the linear dependence of PCL core crystallinity on flow rate. Furthermore, PAX loading efficiency was dependent on PNP size and morphology. Formulations which consisted of cylindrical and lamellar type morphologies typically had higher PAX loading efficiencies, than formulations which consisted of spherical structures. Next, we studied diffusional PAX release, increasing core crystallinity correlated with slowing diffusional PAX release kinetics. At high drug loading ratios (r > 0.1), we demonstrated reproducible control of PAX-loaded PNP structure and function. PCL core crystallinity was a major factor influencing PNP size and morphology. Samples with high core crystallinity formed PNP structures with low internal curvature. Furthermore, core crystallization had a large influence on PAX loading efficiency; as samples with high PAX loading efficiency correlated with low PCL core crystallinity. With respect to diffusional PAX release, we found that increasing PCL core crystallinity correlated with slowing diffusional PAX release kinetics. Next, we studied the cytotoxicity of our PAX-loaded PNPs using the MCF-7 cancer cell line. Due to the complex nature of the interactions between our PAX-loaded PNPs and the cancer cells, we were not able to elucidate the exact influence of flow rate on PNP cytotoxicity. / Graduate

This dissertation presents the synthesis of stimuli-sensitive hydrophilic polymers, particularly doubly responsive hydrophilic block copolymers, by controlled radical polymerizations and the study of their solution behavior in water. By incorporating a small amount of stimuli-responsive groups into the thermosensitive block of a hydrophilic block copolymer, the lower critical solution temperature (LCST) of the thermosensitive block can be tuned by a stimulus and multiple micellization/dissociation transitions can be achieved by combining two external triggers. Chapter 1 describes the synthesis and thermosensitive properties of two new watersoluble polystyrenics with a short oligo(ethyl glycol) pendant from each repeat unit and the study of hydrophobic end group effects on cloud points of thermosensitive polystyrenics. Well-defined polymers were prepared from monomer-based initiators via nitroxide-mediated polymerization and the alkoxyamine end groups were removed by tri(n-butyl)tin hydride, yielding thermoresponsive polystyrenics with essentially no end groups. The results showed that hydrophobic end groups could significantly change the cloud points and the molecular weight dependences of cloud points of polystyrenics. Chapter 2 presents the synthesis of thermo- and light-sensitive hydrophilic block copolymers, poly(ethylene oxide)-b-poly(ethoxytri(ethylene glycol) acrylate-co-onitrobenzyl acrylate), and their responsive behavior in dilute aqueous solutions. Dynamic light scattering and fluorescence spectroscopy studies showed that these copolymers were molecularly dissolved in water at lower temperatures and self-assembled into micelles at temperatures above the LCST of the thermosensitive block. Upon UV irradiation, the oiv nitrobenzyl group was cleaved and the LCST of the thermosensitive block was increased, causing the dissociation of micelles into unimers. The resultant copolymers underwent thermo-induced reversible micellization at higher temperatures. Chapter 3 describes multiple micellization/dissociation transitions of thermo- and pH-sensitive hydrophilic block copolymers, poly(ethylene oxide)-b-poly(methoxydi(ethylene glycol) methacrylate-co-methacrylic acid), in response to temperature and pH changes. The LCST of the thermosensitive block can be reversibly tuned and precisely controlled by solution pH. Chapter 4 presents the study on multiple sol-gel-sol transitions of a 20.0 wt % aqueous solution of poly(ethylene oxide)-b-poly(ethoxytri(ethylene glycol) acrylate-co-o-nitrobenzyl acrylate) induced by temperature changes and UV irradiation. The solution underwent thermo-induced sol-gel-sol transitions. Upon UV irradiation to dissociate micelles, the gel was transformed into a free-flowing liquid, which upon heating underwent sol-gel-sol transitions again.

Produced water is a major waste produced from oil and natural gas wells in the state of Texas. This water could be a possible source of new fresh water to meet the growing demands of the state after treatment and purification. This thesis describes a research project that evaluated the treatment of brine generated in oil fields (produced water) with ultrafiltration membranes. The characteristics of various ultrafiltration membranes for oil and suspended solids removal from produced water were studied to test whether they could be used in a pretreatment method. The research measured the effect of pressure and flow rate on performance of three commercially available membranes for treatment of oily produced water. Oil and suspended solids removal were measured by using turbidity and oil in water measurements taken periodically. The study also analyzed the flux through the membrane and any effect it had on membrane performance. The research showed that an ultrafiltration membrane provided turbidity removal of over 99% and oil removal of 78% for the produced water samples. The results indicated that the ultrafiltration membranes would be useful as one of the first steps in purifying the water. Membrane cleaning of produced water-fouled membranes by micellar solutions was investigated. A neutral pH and ambient temperature micelle solution for effective cleaning of oily water-fouled membranes was developed and studied. The performance of cleaning solutions on ultrafiltration membranes was investigated on laboratory size membrane testing equipment. Different micro emulsion solutions were studied to evaluate the effect of solution properties on cleaning performance. Three types of multiple membranes were studied, each having the same polyvinylidene fluoride (PVDF) material but with different nominal separation or flux characteristics. The data showed that the use of a micelle solution to clean the produced water-fouled membranes was a feasible and effective method. The study showed with further adjustment of the micelle solution the cleaning effectiveness could be optimized to provide double the effectiveness of current industry methods for membranes fouled by produced water.