The benefits of controlled release drug delivery are important to the pharmaceutical industry. With a controlled release device, local administration of a drug is possible and release profiles can be created that remain within therapeutic limits for prolonged periods. Made from biodegradable and bioerodable polymers, unwanted side effects and the need of return trips for treatment diminish. However, a usable device must be free of organic solvents normally used to dissolve large drug molecules. Many of these solvents are toxic themselves. Therefore, steps must be taken to either remove residual solvent from the final device or limit their use during synthesis. Ideally, it is desirable to remove the organic solvents from the process entirely. Supercritical carbon dioxide (scCO2) has been used as a replacement for these solvents. Carbon dioxide is inexpensive, environmentally acceptable, and safe for use in human consumables. However, many drug molecules have very low solubility in scCO2, resulting in extended polymer impregnation times. An organic co-solvent can be used to increase drug solubility, leading to a more efficient polymer impregnation. Using only a small amount of organic co-solvent, a single phase stream is possible that results in significantly increased solubility. This meets the original task of limiting organic solvents in the process and increases efficiency over scCO2 alone. This study uses supercritical carbon dioxide with ethanol as a co-solvent. Ethanol increases the solubility of β-estradiol in scCO2 for impregnation into the glassy polymer polyvinylpyrrolidone (PVPP). Experimental conditions cover a range of temperatures from 40 °C to 50 °C and pressure up to 2500 psi. The effect of polymer swelling time on the sorption process is also studied. A dual mode sorption model describes the sorption of drug into the glassy polymer, and a plug flow and stirred tank compartmental model predicts breakthrough profiles. The determined sorption parameters allow analysis of polymer conformation and suggest optimum impregnation conditions.

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The use of supercritical carbon dioxide (scCO₂) as a processing aid to help exfoliate nano-clays and improve their dispersion during melt blending in polymer matrices has been reported in the literature. One of the best processes in terms of improving the degree of nano-clay dispersion and composite mechanical properties was developed in our laboratory. This process allows the clay to be in direct contact with scCO₂ and expanding the clay-CO₂ mixture via rapid depressurization into a two-stage screw extruder to mix with the polymer pellets. However, composites with clay loading higher than 6.6 wt % were not reported. In addition, the scCO₂ aided processing method has not been applied to carbon nanotube (CNT) based composites. This dissertation initially focused on applying the scCO₂ aided processing technique to the field of CNT expansion and CNT/polymer composite preparation. The relationship with the expanded CNT morphology and the experimental conditions of the expansion procedure (including pressures, temperatures, exposure time, and depressurization rates) was studied. Microscopy results showed improved CNT dispersion in the polymer matrix and more uniform networks formed with the use of scCO₂, which indicated that CO₂ expanded CNTs are easier to disperse into the polymer matrix during the blending procedure. The CNT/ poly(phenylsulfone) (PPSF) composites prepared with scCO₂ aided method provided continuous improvements in Young's modulus up to the addition of 7 wt % CNTs. However, the Young's modulus of the composite prepared by means of conventional direct melt blending failed to increase beyond the addition of 1 wt % CNT. The second part of this work is concerned with the development of a semi-continuous process using scCO₂ to process polymer-clay composites with clay loading higher than 6.6 wt % (i.e. 10 wt %). Two major modifications are involved in the new procedure: exfoliating the nano-clay directly into the hopper filled with pellets followed by processing the composite immediately and sequentially mixing the clay into the melt. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) results show that this modified procedure help to reduce the clay collapse when processing the composites with high clay loadings. Surface modified montmorillonite (MMT) nano-clay/polypropylene (PP) composite at 10 wt % nano-clay with improved clay dispersion was obtained with increased modulus and tensile strength of 63 % and 16%, respectively, compared to the pure PP matrix. Additional mechanical property improvements for nano-clay based composites are then obtained with the use of high crystallinity polypropylene (HCPP) and polypropylene grafted with maleic anhydride (PP-g-MA). HCPP has higher crystallinity and stiffness than conventional PP and, therefore, composites made from HCPP have better mechanical properties to start with. PP-g-MA has polar groups grafted on the PP chains that promote the intercalation of PP with clay. By using the newly developed procedure, the HCPP nanocomposite at 10 wt % of nano-clay has a Young's modulus as high as 3.236 GPa, and the modulus of the 10% MMT/PP-g-MA sample is found to be 2.595 GPa, both higher than that of the composite prepared by the direct blending method and that of a composite based on a conventional PP matrix. / Ph. D.

In this thesis, silicon oxide thin films fabricated on silicon substrates by reactive radio frequency (rf) magnetron sputtering and supercritical CO2 (SCCO2) treatment at room temperature were investigated. The electrical properties including I-V and C-V of the films prepared at different processing conditions were discussed. Using the Transmission Electron Microscope (TEM), the thickness of silicon oxide thin films were measured. The results suggested that the film quality can be significantly improved by the SCCO2 treatment after reactive sputtering. The leakage current of the films at an electrical field of 1 MV/cm is 1¡Ñ10-8A/cm2 with a hysteresis voltage of 0.01V. The silicon oxide thin films can be used as a barrier layer for Al/SiO2/Si silicon solar cells. The energy conversion efficiency of a single crystal silicon solae cell is 10.2% under AM1.5 (965W/m2) radiation. After rapid thermal annealing(RTA) at 500¢J, the measured short-circuit current, open- circuit voltage, fill factor are 53mA, 0.54V and 0.53, respectively.

Experimental thermal-hydraulic study of a rectangular supercritical CO2 natural-circulation loop with a horizontal heated channel was conducted at different steady-state conditions. These included different system pressures and three different inlet temperatures, with different inlet and outlet valve openings. Approximately, 450 experimental steady-state data-points were collected. The data include measurements of pressure-drop along the heated channel, pressure-drop across inlet and outlet valves, applied heat on the heated channel, pressure, temperature and flow-rate. Steady-state curves of mass flow-rate versus power, outlet temperature versus power, and detailed information of frictional pressure drop and local head loss coefficients were produced. Comparison showed that for the available experimental set-up, computed frictional pressure-drops fell within 1-1.20 of the Blasius formula prediction. Moreover, flow oscillations were observed in several cases when outlet temperature of CO2 was higher than the pseudo-critical temperature on the negative slope part of the mass flow-rate versus power curve.

L’utilisation d’outils microfluidiques pour la mise en œuvre de procédés sous-pression tels que des réactions chimiques, des synthèses de matériaux nano-structurés, ou en tant qu’outils de détermination de grandeurs physico-chimiques est une thématique de recherche récente. Quelques travaux précédents ont démontré l'intérêt des procédés supercritiques en microcanal pour la chimie organique et la synthèse de nanocristaux. Le développement de ces procédés est concomitant à la mise au point de dispositifs capables de résister à des conditions de pression et température élevées tout en étant compatibles avec l’utilisation de fluides supercritiques. Les avantages de ces fluides pour ce type de procédé sont une faible viscosité et une diffusivité élevée, ce qui offre des conditions de mélange favorables. Cependant, dans le même temps, les propriétés de transport – comme la masse volumique – sont très sensibles aux variations de température et de pression, qui ne peuvent être évités dans ces systèmes où les fluides sont en écoulement. Dans des systèmes diphasiques où le CO2 supercritique (PC = 74 bar) est utilisé en tant que solvant, les transferts thermique et de matière sont fortement influencés par la nature des écoulements. Dans un souci de maîtrise de ces procédés, la compréhension du comportement hydrodynamique, à la fois locale et globale, des fluides supercritiques en microcanal devient fondamentale. Dans cet objectif, un dispositif de microfluidique transparent et résistant à des pressions supérieures à la pression critique du CO2 a été développé. En adaptant une méthodologie propre à la lithographie molle, permettant la fabrication de puces microfluidiques pour des applications à pression atmosphérique, nous sommes parvenus à établir un protocole de fabrication de puces en verre et résine photosensible, viables pour une utilisation à plus de 100 bar en conditions CO2 supercritique. Grâce à ces dispositifs, des expérimentations d’ombroscopie ont pu être réalisées pour observer des écoulements composés de CO2 et d’éthanol dans le microcanal de section carrée de 200 x 200 µm à des pressions comprises entre 40 et 90 bar. Pour identifier et comprendre les phénomènes qui entrent en jeu lors de la création de l’écoulement à haute pression, une approche thermodynamique relative aux équilibres de phase est indispensable. En effet, la connaissance du diagramme de phase permet d’ores et déjà de représenter les zones d’équilibres thermodynamiques (pression, température et composition) pour lesquelles le mélange créé est monophasique liquide ou diphasique liquide-vapeur. L’illustration expérimentale par les séquences d’écoulement obtenues justifie la modélisation thermodynamique du diagramme de phase du binaire d’étude. Le régime d’écoulement de Taylor, obtenu spécifiquement à l’intérieur de la zone d’équilibre diphasique liquide-vapeur, est étudié. Ce régime est caractérisé par des bulles allongées entourées par un film liquide et séparées les unes des autres par une poche liquide. L’évolution des caractéristiques hydrodynamiques de ce régime – longueur de bulle, longueur de slug et vitesse de bulle – est étudiée en fonction des conditions opératoires, des débits et propriétés des fluides. L’objectif étant de repérer les similitudes avec les caractérisations à pression ambiante de la littérature et les particularités résultantes d’une manipulation à haute pression. Ce travail a été à l’origine de plusieurs avancées pour les communautés microfluidique et supercritique. Un nouveau protocole de fabrication à moindre coût de puces microfluidiques compatibles avec l’utilisation de CO2 supercritique et des méthodes de visualisation avancées est présenté. Une modélisation thermodynamique et une étude hydrodynamique expérimentale permettent de construire une carte d’écoulement des régimes biphasiques observés à haute pression ainsi qu’une caractérisation hydrodynamique du régime de Taylor à haute pression en microcanal. / The use of microdevices to run high pressure processes for chemical reaction, nanomaterial synthesis, or as analysis tools for determining physical properties have become of increasing interest in recent years. Several works in the literature have demonstrated the advantages of supercritical microfluidics for organic chemistry and complex nanomaterial synthesis. The development of pressure-resistant microfluidic chips, which also are compatible with the properties of supercritical fluids, is a key step in order to increase knowledge about these processes. Supercritical fluids have low viscosity and high diffusivity, which are advantageous for microprocesses since they facilitate mixing between species. However, the properties of these fluids are also very sensitive with small changes in pressure, temperature and composition. In twophase applications where supercritical CO2 may be used as solvent or reactant, these varying properties can result in very different flow patterns and hydrodynamics with pressure change. Since the hydrodynamics of such systems largely influence heat and mass transfer, the study of flow behavior under supercritical conditions in microchannel is fundamental. In pursuit of this objective, a transparent microdevice, which is suitable for experiments at pressures higher than critical pressure of CO2 (PC = 74 bar), has been developed in this thesis. Using a soft lithography method that is currently used to fabricate microfluidic chips for applications under ambient pressure, a methodology for fabricating a highly resistant chip made from glass and UV-curable polymer was developed. These chips can resist more than 100 bar in supercritical CO2 conditions. The microchips were then used to observe the flow behavior of a CO2-ethanol mixture created in a T junction microchannel (cross section: 200 x 200 µm) for pressures ranging from 40 to 90 bar using high-speed imaging. To identify and interpret phenomena that occur during the flow formation at high pressure, a thermodynamic approach was essential. Depending on the pressure, temperature and composition of the CO2-ethanol mixture, the flow at equilibrium can either be in the single phase liquid domain or in the two-phase liquid vapor domain, according to the phase diagram. Imaging experiments were conducted over the boundaries between the two-phase liquid vapor domain and the single phase liquid and the observed two-phase flow patterns and transitions confirm the predictions of the phase diagram. High-pressure CO2-ethanol Taylor flow, which was obtained in the twophase domain, was then studied. This flow pattern, which is characterized by elongated bubbles surrounded by a liquid film and separated from each other by liquid slugs, is well-known at low pressure and has been widely described in the literature. The objective here was therefore to compare the flow characteristics such as bubble length, slug length and bubble velocity obtained under high pressure operation with the behavior at low pressure. Differences coming from fluid characteristics or operating at high pressure were pointed . This work provides a variety of new results on high pressure microfluidics that will be of interest to both the microfluidics and the supercritical fluids communities. It presents a new protocol to fabricate low cost pressure-resistant microfluidic chips suitable for supercritical CO2 and advanced visualization methods. It also presents new findings obtained with this technology on map flow pattern at high pressure in correlation with thermodynamics approach and characterization of Taylor flow hydrodynamics under high pressure in microchannel.

Carbon capture and storage (CCTS) is a transitional technology offering a nearterm method of mitigating climate change. Pipelines are considered to be the most suitable systems for CCTS; however, structural integrity of pipeline has to be guaranteed in order for this technology to become a practical technical solution. The investigation detailed here is based on a systematic experimental approach to investigate the structural integrity of API X100, X60 and X70 steels exposed in simulated flue-gas under dynamic conditions. A core of the structured experiments through some methods such as aging test, tensile properties, fracture toughness, residual stress and engineering critical assessment was accomplished in parent material and exposed samples on flue-gas. The temperature range of evaluation for tensile test covers -70C to 21C while fracture toughness was over the range -196C to 21C. Tensile properties of virgin material show that steels meet standard specification while aging samples do not show significant scatter compared with parent steels. Ovalisation of the fracture surface and splitting phenomenon was observed which is related with steel anisotropy. Fracture toughness obtained from experiment was compared with that calculate by two existing correlations. However both correlations did not predict the level of fracture toughness expected indicating the methods used in this work has limited applicability under the test conditions used here. Residual stress (RS) induced in API X100 steel by cold rolling method was characterised using two complementary techniques known as Neutron Diffraction (ND) and Incremental Hole Drilling (IHD). The RS distribution shows good agreement for both techniques used but reproducibility of them depends on their own inaccuracies. An Engineering Criticality Assessment (ECA) was performed based in Failure Assessment Diagram (FAD) approach using all the experimental data obtained by a leak-before-break method under three operational pressures. The results showed the effect on the integrity of material under the presence of a flaw length assessed. Overall, the thesis presents a combined engineering critical assessment which involved the examination of materials used to transport flue-gas and established a methodology to determine fracture toughness alongside with the FAD to assess the integrity of pipelines.

Methylsilsesquioxane (MSQ) and organosilicate glass (OSG) are the materials under this study because they exhibit the dielectric constant values necessary for future IC technology requirements. Obtaining a low-k dielectric value is critical for the IC industry in order to cope time delay and cross talking issues. These materials exhibit attractive dielectric value, but there are problems replacing conventional SiO2, because of their chemical, mechanical and electrical instability after plasma processing. Several techniques have been suggested to mitigate process damage but supercritical silylation offers a rapid single repair step solution to this problem. Different ash and etch damaged samples were employed in this study to optimize an effective method to repair the low-k dielectric material and seal the surface pores via supercritical fluid processing with various trialkylchlorosilanes. Fourier transform infrared spectroscopy (FTIR), contact angle, capacitance- voltage measurements, and x-ray photoemission spectroscopy, dynamic secondary ion mass spectroscopy (DSIMS), characterized the films. The hydrophobicity and dielectric constant after exposure to elevated temperatures and ambient conditions were monitored and shown to be stable. The samples were treated with a series of silylating agents of the form R3-Si-Cl where R is an alkyl groups (e.g. ethyl, propyl, isopropyl). Reactivity with the surface hydroxyls was inversely proportional to the length of the alkyl group, perhaps due to steric effects. Contact angle measurements revealed that heating the films in ambient diminished hydrophobicity. Depth and surface profiling using (DSIMS) and (XPS) were utilized to develop a model for surface coverage.

L'amélioration des systèmes énergétiques est considérée comme un levier technologique pour répondre aux défis liés à la croissance de la demande d’électricité et des émissions des gaz à effet de serre. Les futures centrales devraient présenter une intégration thermique plus flexible et des sources de chaleur mixtes possibles. Une des solutions fiables consiste à utiliser un cycle de Brayton au CO2 supercritique (CO2-SC), un tel cycle à haut rendement est théoriquement prometteur pour les applications nucléaires, fossiles et solaires thermiques. Un des principaux obstacles au déploiement du cycle de Brayton au CO2-SC est de justifier sa faisabilité, sa viabilité et son potentiel à l’échelle industrielle. Dans ce contexte deux axes de recherche ont été identifiées : • Une sélection rigoureuse de l’équation d’état qui permet de représenter les propriétés d’intérêt du CO2-SC. • Une nouvelle méthodologie pour l’optimisation des centrales électriques, permettant de sélectionner automatiquement le procédé optimal parmi une grande quantité de configurations possibles (dénomme superstructure). Les résultats de la première partie de cette thèse mettent en lumière que l’équation de SW est pertinente pour limiter l’impact de l’imprécision de l’équation d’état sur le dimensionnement du procédé. Dans cette thèse, un simulateur de procédé commercial, ProSimPlus a été combiné avec un solveur type évolutionnaire (MIDACO) afin d’effectuer des optimisations superstructure. Premièrement, le critère d’optimisation est de maximiser le rendement énergétique du procédé. Dans un deuxième temps, on cherche simultanément à minimiser les coûts du procédé. Pour ce faire, des fonctions de coût internes à EDF ont été utilisées afin de permettre l’estimation des coûts d'investissement (CAPEX), des dépenses opérationnelles (OPEX) et du coût actualisé de l'électricité (LCOE) / Efficiency enhancement in power plant can be seen as a key lever in front of increasing energy demand. Nowadays, both the attention and the emphasis are directed to reliable alternatives, i.e., enhancing the energy conversion systems. The supercritical CO2 (SC-CO2) Brayton cycle has recently emerged as a promising solution for high efficiency power production in nuclear, fossil-thermal and solar-thermal applications. Currently, studies on such a thermodynamic power cycle are directed towards the demonstration of its reliability and viability before the possible building of an industrial-scale unit. The objectives of this PhD can be divided in two main parts: • A rigorous selection procedure of an equation of state (EoS) for SC-CO2 which permits to assess influences of thermodynamic model on the performance and design of a SC-CO2 Brayton cycle. • A framework of optimization-based synthesis of energy systems which enables optimizing both system structure and the process parameters. The performed investigations demonstrate that the Span-Wagner EoS is recommended for evaluating the performances of a SC-CO2 Brayton cycle in order to avoid inaccurate predictions in terms of equipment sizing and optimization. By combining a commercial process simulator and an evolutionary algorithm (MIDACO), this dissertation has identified a global feasible optimum design –or at least competitive solutions– for a given process superstructure under different industrial constraints. The carried out optimization firstly base on cycle energy aspects, but the decision making for practical systems necessitates techno-economic optimizations. The establishment of associated techno-economic cost functions in the last part of this dissertation enables to assess the levelized cost of electricity (LCOE). The carried out multi-objective optimization reflects the trade-off between economic and energy criteria, but also reveal the potential of this technology in economic performance.

Dans le cadre du développement des réacteurs nucléaires de 4ème génération et plus particulièrement du réacteur à neutrons rapides refroidi au sodium (SFR), le CO2 supercritique, dans un cycle de Brayton, a été identifié comme fluide potentiel en remplacement de la vapeur d'eau dans le cycle de conversion de l'énergie. Les aciers ferrito-martensitiques contenant 9 à 12 % en poids de Cr sont de bons candidats pour la réalisation d'échangeurs thermiques car ils présentent de bonnes propriétés mécaniques jusqu'à une température de 600°C, une forte conductivité thermique, un faible coefficient d'expansion thermique ainsi qu'un coût plus faible que celui des aciers austénitiques. Cependant, il a été montré que ces aciers forment une couche d’oxyde à croissance rapide et carburent fortement dans les conditions du circuit de conversion d'énergie (550°C, 250 bar).Cette étude a pour objectif d’étudier l’influence de différents paramètres (les impuretés présentes dans le CO2, les vitesses de rampe thermique ainsi que l’état de surface) sur le mécanisme d’oxydation d’un acier Fe-12Cr dans le CO2 à 550°C. Il est montré qu’en fonction de la valeur de ces paramètres, il est possible de former une couche d’oxyde fine protectrice en surface sans carburation. Un modèle permettant de rendre compte de l’ensemble des résultats expérimentaux est proposé. / In the framework of the development of Sodium Fast Reactors in France, supercritical carbon dioxide integrated in the Brayton cycle is proposed as new cycle energy conversion system to replace current steam generators. Ferritic-Martensitic steels with 9-12 wt% Cr are good candidates for heat exchanger application because they have good mechanical properties up to a temperature of 600°C, a high thermal conductivity, a low coefficient of thermal expansion and a lower cost than that of austenitic steels. However, it has been found that these steels present a high parabolic oxide growth rate and a strong carburization in the temperature and pressure conditions of the SC-CO2 cycle (550°C, 250 bar).This study aims to investigate the influence of different parameters (impurities present in CO2, thermal ramp rate and surface state) on the oxidation mechanism of a Fe-12 Cr steel in CO2 at 550°C. It has been shown that depending on these parameters, a thin protective oxide scale without any strong carburization can be obtained. A model is proposed to explain the experimental results.