This Ph.D. research project targets Cooper Basin oil reservoirs of very low permeability (approximately 1mD) where injectivities required for water flooding are not achievable. However, the use of injection gases such as CO₂ would not have injectivity problems. CO₂ is abundant in the region and available for EOR use. CO₂ was compared to other CO₂-rich injection gases with a hydrocarbon content including pentane plus components. While the effect of hydrocarbon components up to butane have been investigated in the past, the effect of n-pentane has on impure CO₂ gas streams has not. One particular field of the Cooper Basin was investigated in detail (Field A). However, since similar reservoir and fluid characteristics of Field A are common to the region it is expected that the data measured and developed has applications to many other oil reservoirs of the region and similar reservoirs elsewhere. The aim of this Ph.D. project is to determine the applicability of CO₂ as an injection gas for Enhanced Oil Recovery (EOR) in the Cooper Basin oil reservoirs and to compare CO₂ with other possible CO₂-rich injection gases. The summarised goals of this research are to: • Determine the compatibility of Field A reservoir fluid with CO₂ as an injection gas. • Compare CO₂ to other injection gas options for Field A. • Development of a correlation to predict the effect of nC₅ on MMP for a CO₂- rich injection gas stream. These goals were achieved through the following work: • Extensive experimental studies of the reservoir properties and the effects of interaction between CO₂-rich injection gas streams and Field A reservoir fluid measuring properties related to: • Miscibility of the injection gas with Field A reservoir fluid • Solubility and swelling properties of the injection gas with Field A reservoir fluid • Change in viscosity-pressure relationship of Field A reservoir fluid due to addition of injection gas • A reservoir condition core flood experiment • Compositional simulation of the reservoir condition core flood to compare expected recoveries from different injection gases • Development of a set of Minimum Miscibility Pressure (MMP) measurements targeted at correlating the effect of nC₅ on CO₂ MMP. The key findings of this research are as follows: • Miscibility is achievable at practical pressures for Field A and similar reservoir fluids with pure CO₂ or CO₂-rich injection gases. • For Field A reservoir fluid, viscosity of the remaining flashed liquid will increase at pressures below ~2500psi due to mixing the reservoir fluid with a CO₂-rich injection gas stream. • Comparison of injection gases showed that methane rich gases are miscible with Field A so long as a significant quantity of C₃+ components is also present in the gas stream. • There is a defined trend for effect of nC₅ on MMP of impure CO₂. This trend was correlated with an error of less than 4%. • Even though oil composition is taken into account with the base gas MMP, it still affects the trend for effect of nC₅ on MMP of a CO₂-rich gas stream. • An oil characterisation factor was developed to account for this effect, significantly improving the results, reducing the error of the correlation to only 1.6%. The significance of these findings is as follows: • An injection pressure above ~3000psi should be targeted. At these pressures miscibility is achieved and the viscosity of the reservoir fluid injection gas mix is reduced. • CO₂ should be compared to gases such as Tim Gas should after considering the cost of compression, pipeline costs and distance from source to destination will need to be considered. • The addition of nC₅ will reduce the MMP and increase the recovery factor, however the cost of the nC₅ used would be more than the value of increased oil recovered. • The developed correlation for the effect of nC₅ on impure CO₂ MMP can be used broadly within the limits of the correlation. • Further research using more oils is necessary to validate the developed oil characterisation factor and if successful, using the same or similar method used to improve other correlations. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1369016 / Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum, 2009.

The overall objective of this PhD thesis research is to understand and control phase separation in mixed perfluorinated fatty acid-phospholipid surfactant systems that have applications as pulmonary surfactant (PS) mixtures, with an ultimate view of controlling film composition, morphology and mechanical properties. In this context the interaction between perfluorooctadecanoic acid (C18F), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), the major component of native PS extract, and 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) has been explored in Langmuir monolayers and Langmuir–Blodgett (LB) films using a combination of atomic force microscopy (AFM), fluorescence microscopy (FM) and Brewster angle microscopy (BAM) measurements. Thermodynamic and morphological studies of binary and ternary mixed films made of C18F, DPPC and DPPG indicated that both the phospholipids and C18F were miscible over a wide range of compositions. The mixed phospholipid-C18F films contained multimolecular aggregates that were highly enriched in the phospholipids. Furthermore, it was found that the magnitude of the DPPC-C18F interaction could be modulated by altering the concentration of sodium ions in the underlying subphase. Using a highly simplified lung mimic fluid (pH 7.4, 150mM NaCl), DPPC and C18F became fully immiscible. Moreover, the performance characteristics of the mixed films demonstrated the usefulness of C18F as an additive for PS formulations. The effectiveness of a PS protein mimicking peptide was evaluated against DPPC to allow comparison with previous measurements of DPPC-C18F mixed system. The mixing thermodynamics of the peptide and DPPC in Langmuir monolayer implied a repulsive interaction between the film components. The hysteresis response of the mixed monolayer films indicated that the lipid-protein mixture improved the re-spreading of DPPC films. Moreover, molecular-level organization of the mixed films explored by both FM and BAM confirmed the formation of liquid-expanded DPPC domains in the presence of minute amount of the peptide. In order to obtain a thorough understanding of the effect of the deposition process and surfactant tail polarities on the interfacial behavior of perfluorocarbon-hydrocarbon mixed monolayer films, both BAM and AFM measurements of arachidic acid (C20) with perfluorotetradecanoic acid (C14F) and palmitic acid (C16) with C18F mixed monolayer were performed. These measurements revealed that film morphology was minimally perturbed upon its deposition onto solid substrates. Coarse grained molecular dynamics (MD) simulations of films comprised of DPPC molecules with tails of various polarities suggested that the phase separation between the monolayer components could be controlled by varying surfactant tail polarities.

Bose-Einstein condensation (BEC) is a phenomenon in which identical bosons occupy the same quantum state below a certain critical temperature. A hallmark of BEC is the coherence between particles every particle shares the same quantum wavefunction and phase. This coherence has been demonstrated for the external (motional) degrees of freedom of the atomic condensates by interfering two condensates. In this thesis, the coherence is shown to extend to the internal spin degrees of freedom of a spin-1 Bose gas evidenced by the observed coherent and reversible spin-changing collisions. The observed coherent dynamics are analogous to Josephson oscillations in weakly connected superconductors and represent a type of matter-wave four-wave mixing. Control of the coherent evolution of the system using magnetic fields is also demonstrated. The studies on spinor condensates begin by creating spinor condensates directly using all-optical approaches that were first developed in our laboratory. All-optical formation of Bose-Einstein condensates (BEC) in 1D optical lattice and single focus trap geometries are developed and presented. These techniques offer considerable flexibility and speed compared to magnetic trap approaches, and the trapping potential can be essentially spin-independent and are ideally suited for studying spinor condensates. Using condensates with well-defined initial non-equilibrium spin configuration, spin mixing of F = 1 and F = 2 spinor condensates of rubidium-87 atoms confined in an optical trap is observed. The equilibrium spin configuration in the F = 1 manifold confirms that 87Rb is ferromagnetic. The coherent spinor dynamics are demonstrated by initiating spin mixing deterministically with a non-stationary spin population configuration. Finally, the interplay between the coherent spin mixing and spatial dynamics in spin-1 condensates with ferromagnetic interactions is investigated.

Made available in DSpace on 2016-12-08T17:19:14Z (GMT). No. of bitstreams: 1 iniciais.pdf: 130139 bytes, checksum: cfb58dd0103455dbb6c7b372a4cf5ad3 (MD5) Previous issue date: 2005-02-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Aiming the study of miscibility and mechanical properties, blends of poli(styrene-coacrylonitrile) (SAN) with poli(butadiene-co-acrylonitrile) (NBR) rubbers were prepared by casting, co-precipitation and extrusion followed by injection, varying acrylonitrile (AN) contents from 32,7 to 45% (w/w) in NBR. The blends were prepared in the compositions: SAN/NBR 90/10, 80/20, 70/30, 60/40 and 50/50 (w/w) and valued by Infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), Scanning electron micrographs (SEM), Tensile and Izod impact tests. FTIR analyses of casting blends displayed that not happened reactions or specific interactions between polymers during blending because did not happened a shift in the spectrum blends bands. The DSC analyses of casting blends showed total imiscibility to SAN/NBR 50/50 blend (AN contents in NBR 32,7%), partial miscibility to the 60/40, 70/30 and 80/20 compositions and total miscibility to the 90/10 composition. The SAN/NBR blends (AN contents in NBR 39%), prepared by casting and coprecipitation revealed partial miscibility for all compositions. Coprecipitated blends prepared with AN rubber content of 45% showed partial miscibility to 50/50, 60/40, 70/30 and 90/10 compositions and total miscibility to 80/20 composition. The phase morphology was influenciated by blending methods, casting blends revealed dispersed spherical elastomeric domains in matrix while coprecipitated blends form co continuous phase. The NBR addition result in significant impact resistant increase but decrease in tensile strenght / Com o objetivo de estudar a miscibilidade e propriedades mecânicas, foram preparadas blendas do copolímero poli(estireno-co-acrilonitrila) (SAN) com o copolímero poli(butadienoco-acrilonitrila) (NBR). As blendas foram preparadas por três métodos diferentes: evaporação de solvente, co-precipitação e extrusão seguida de injeção, variando o teor de acrilonitrila no NBR de 33 a 45 % (m/m). As blendas foram preparadas nas composições SAN/NBR 90/10, 80/20, 70/30, 60/40 e 50/50 (m/m) e avaliadas por Espectroscopia na região do infravermelho com Transformada de Fourrier (FTIR), Calorimetria diferencial exploratória (DSC), Microscopia eletrônica de varredura (MEV), Ensaios de Tração e Impacto Izod. As análises de FTIR das blendas preparadas por evaporação de solvente mostraram não ter ocorrido nenhuma reação nem interação específica entre os polímeros durante o processo de mistura porque não houve deslocamentos, aparecimento ou desaparecimentos de picos no espectro das blendas em relação ao espectro dos polímeros puros. O DSC avaliou a miscibilidade das blendas preparadas por evaporação de solvente e co-precipitação. A blenda SAN/NBR 50/50, preparada por evaporação de solvente, (NBR contendo 32,7% de acrilonitrila), é totalmente imiscivel, as composições 60/40, 70/30 e 80/20 são parcialmente miscíveis e a composição 90/10 formou um sistema miscível. As blendas SAN/NBR (NBR contendo 39% de acrilonitrila), preparadas por evaporação de solvente e co-precipitação, mostraram-se parcialmente miscíveis em todas as composições. As blendas preparadas por co-precipitação usando a borracha com 45% de acrilonitrila são parcialmente miscíveis com exceção da composição 80/20 que é totalmente miscível. A morfologia de fase foi influenciada pelo método de preparação das blendas, aquelas preparadas por evaporação de solvente mostraram domínios elastoméricos ovais dispersos na matriz SAN, enquanto que as preparadas por coprecipitação apresentaram fases semi-contínuas. A resistência ao impacto foi significativamente aumentada pela incorporação do NBR no SAN porém com decréscimo do Módulo de Young.

Neste trabalho foram efetuados estudos importantes e pioneiros sobre as propriedades estruturais, eletrônicas e termodinâmicas dos nitretos e de suas ligas, através de dois métodos de primeiros princípios distintos, o FLAPW (\"Full-potential Linear Augmented Plane Wave\") e o pseudopotencial combinado com a aproximação quasequímica generalizada. Na primeira parte, utilizando o método FLAPW, calculamos as estruturas de bandas para os nitretos cúbicos do grupo-IH, BN, AIN, GaN e InN. Foram obtidos valores para a constante de rede e \"bulk modulus\" para os nitretos do grupo-III através de cálculos relativísticos da energia total. Através das estruturas de bandas e analisando o topo da banda de valência e o fundo da banda de condução perto do ponto r ou, no ponto k correspondente ao mínimo da banda de condução, derivamos os respectivos valores para as massas efetivas de elétron e de buraco pesado, leve e de \"split-off\' e correspondentes parâmetros de Luttinger. Todos os resultados são comparados com dados experimentais e teóricos existentes na literatura. Na segunda parte, utilizando o método FLAPW, estudamos a influência da impureza de Mg na estrutura eletrônica do GaN cúbico (c-). Realizamos cálculos da otimização da geometria, incluindo deslocamentos dos primeiros e segundos vizinhos, para os casos da impureza com estados de carga neutro e negativo. Obtivemos o valor de 190 meV para o deslocamento de Franck-Condon da energia térmica, o qual apresenta um bom acordo com os dados experimentais de fotoluminescência e efeito Hall. Nós concluímos que os primeiros e segundos vizinhos desempenham um papel importante na determinação das energias do nível aceitador resultante da dopagem do c-GaN com Mg. Na terceira parte, nós apresentamos cálculos das propriedades eletrônicas, estruturais e termodinâmicas de ligas cúbicas envolvendo os nitretos do grupo-III, InxGa1-xN, InxAl-xN, AlxGal-xN, BxGal-xN e BxA1-xN. Nós combinamos o método de expansão de \"clusters\" através da aproximação quasequímica generalizada (\"Generalized Quasichemical Approximation -GQCA\") com cálculos de pseudopotenciais \"ab initio\" DFT-LDA. Para todas a ligas, exceto a de AlxGal-xN, encontramos separação de fase para temperaturas próximas das temperaturas de crescimento. Generalizamos o método de expansão de \"c1usters\" para estudar a influência da tensão biaxial. Encontramos uma significativa supressão da separação de fase induzida pela tensão para as ligas de InxGal-xN e InxAh-xN, sendo no caso da liga de InxGal_xN confirmado experimentalmente. Observamos também que flutuações da energia do \"gap\" da liga de InxGal-xN permitem definir valores mínimo e médio para a energia do \"gap\" com diferentes valores para o \"bowing\". Observamos que a tensão biaxial reduz as flutuações da energia do \"gap\", resultando em uma diminuição do valor do \"bowing\". Através deste estudo mostramos uma possível explicação para a discrepância experimental para valores do \"bowing\". / In this work we performed a pioneer theoretical study of structural, electronic and thermodynamic properties of the group-III nitrides and their alloys, by using two distinct first principles methods, the FLAPW full potential linear augmented plane wave and the pseudopotential-plane-wave method combined with the generalized quasichemical approximation. In the first part of our work, by using the FLAPW, we present the electronic band structures ofthe zinc-blende-type group-III nitrides compounds, BN, AIN, GaN, and InN. Lattice constant and bulk modulus are obtained from fuH relativistic total-energy calculations. Electron, heavy-, light-, and split-off-hole effective masses and corresponding Luttinger parameters are extracted from the band-structure calculations. A comparison with other available theoretical results and experimental data is made. In the second part of our work, by using the FLAPW method, the electronic structure of Mg impurity in zinc-blende (c-) GaN is investigated. Full geometry optimization calculations, including nearest and next-nearest neighbor displacements, were performed for the impurity in the neutral and negatively charged states. A value of 190 meV was obtained for the Franck-Condon shift to the thermal energy, which is in good agreement with that observed in recent low temperature photoluminescence and Hall-effect measurements. We conclude that the nearest and the next-nearest neighbors of the Mg impurity replacing Ga in c-GaN undergo outward relaxations which play an important role in the determination ofthe center acceptor energies. In the third part of our work, we present a study of electronic, structural, and thermodynamic properties of the cubic group-III nitrides alloys, InxGal-xN, InxAll_xN, AlxGal-xN, BxGal-xN e BxAll-xN. We combined the generalized quasichemical approximation (GQCA) with an ab initio pseudopotential-plane-wave method. For alI alIoys, except the AlxGal-xN, we observe a miscibility gap for temperatures near those of the growth. The cluster treatment is generalized to study the influence of biaxial strain. We find a remarkable suppression ofphase separation in InxGal-xN and InxAll-xN induced by strain which is confirmed by experiments on the InxGal_xN alloy. We also observed that the gap fluctuations in the InxGal-xN alloy allow the definition of a minimum gap and an average gap with different bowing parameters. Biaxial strain drastically reduces the gap fluctuations, resulting in a reduction of the bowing. The different gaps and the strain influence investigated provide an explanation for the discrepancies found in the experimental values of the bowing parameter.

Les polysaccharides sont l'une des principales options à retenir pour progresser dans l'utilisation ou la conception de polymères renouvelables. Depuis les années cinquante, le développement industriel de ce type de polymères s'était considérablement réduit du fait de l'avènement des polymères synthétiques. Cependant, cet intérêt a cru considérablement ces dernières années en raison de la sensibilisation du public sur la limite des ressources fossiles. Ces biopolymères sont donc devenus un sujet d'importance, tant sur le plan industriel que sur celui de la recherche fondamentale. Toutefois, les systèmes à base de polysaccharides sont le plus souvent transformés via l'utilisation d'importantes quantités de solvants (y compris l'eau), ce qui globalement pénalise le procédé associé en l'affligeant d'une charge environnementale supplémentaire. Par la voie ‘fondue', le développement de polymères thermoplastiques à base de dérivés de la cellulose est un véritable défi, qui concerne autant le mode de transformation de ces systèmes que le niveau des propriétés du matériau final. Pour exemple, la température de dégradation de l'acétate de cellulose (CA) (dont le degré de substitution 2,5 est développé par le Groupe Solvay) est si proche de sa température de fusion que son procédé de mise en oeuvre ne peut être envisagé qu'avec l'ajout d'une quantité importante de plastifiants externes (entre 20 et 30 en poids selon le type d'additif). Le comportement d'un mélange CA-plastifiant est principalement régi par un «réseau» de très fortes interactions polaires, dont la force et la densité dépendent de 3 paramètres spécifiques: le degré de substitution de CA, la typologie de plastifiant et la quantité de plastifiant. Pour expliquer les différents mécanismes de plastification, il est donc important pour nous d'étudier et de comprendre les propriétés dynamiques (en ce qui concerne les phénomènes de relaxation) de ce type de systèmes et comment les trois leviers que nous avons identifiés peuvent influencer ou moduler les différentes interactions échangées dans les mélanges / Polysaccharides are one of the main options to the on-going move towards the use of renewable polymers. The industrial interest in this type of polymers drastically shrunk by the advent of synthetic polymers in the fifties, but is currently reviving due to the public awareness on the limit of fossil resources. These biopolymers are nowadays offering a challenging and industrially profitable playground for researchers. However, current polysaccharides based materials are mostly processed with extensive use of solvents (including water) making the total process an environmental burden despite the advantage of the starting material. Development of thermoplastic cellulose-based materials is very challenging regarding both final material properties and polymer processing. The degradation temperature of Cellulose Acetate (CA) (degree of substitution 2.5) is so close to its melting temperature that it can only be processed with a significant amount of external plasticizers (between 20 et 30 wt.% depending on the type of the additive). Behavior of a CA-plasticizer blend is mainly governed by a ‘network’ of high polar interactions, the strength and the density of which clearly depend of 3 specific parameters: the CA’s degree of substitution, the typology of the plasticizer, the amount of plasticizer. In an attempt to explain the different plasticization mechanisms, it is thus of utmost importance for us to study and understand the dynamic properties (regarding the relaxation phenomena) of this kind of systems and how the three levers that we identified can influence or modulate the different interactions exchanged within the blends

L’objectif de ces travaux était l’utilisation d’oligomères de polyéthylène fonctionnels comme agents d’interface pour la formulation de matériaux polymères. Une première partie s’est portée sur la compréhension de l’évolution de la morphologie de mélanges composés d’une résine polypropylène ou polyéthylène et d’un oligomère de polyéthylène de faible masse molaire au cours de leur mise en œuvre et de leur cristallisation. Il a été constaté qu’un tel oligomère pouvait être incorporé sans difficulté aux résines sélectionnées, et ce grâce à une diffusion rapide ainsi qu’à une bonne miscibilité à l’état fondu. Cependant, il est apparu que ces mélanges étaient sujets à une séparation de phase solide-liquide lors de leur cristallisation, entraînant la formation de matériaux biphasiques à l’état solide. Dans une deuxième partie, un système réactif composé de deux oligomères fonctionnels a été étudié comme une potentielle stratégie de compatibilisation de mélanges polyéthylène/polyamide. Malgré les morphologies et propriétés intéressantes observées, il a été conclu que l’utilisation d’un tel système réactif n’était pas efficace comparé aux agents compatibilisants usuels. Enfin, des oligomères de polyéthylène fonctionnels ont été étudiés en tant qu’agents d’interface dans du polyéthylène renforcé par des fibres de verre dans l’optique d’en améliorer la facilité de mise en œuvre et les propriétés mécaniques. Il a ainsi été démontré que des oligomères avec les fonctionnalités appropriées pouvaient être utilisés comme agents d’interface en réduisant les interactions interparticulaires au cours de la mise en œuvre et en améliorant l’adhésion interfacial matrice-fibre à l’état solide / The objective of this work was to use end-functionalized polyethylene oligomers as interface agents in glass fibre-reinforced thermoplastics as well as compatibilizer precursors in immiscible polymer blends. The first part of this work was focused on the understanding of the morphology developments occurring during the melt processing and crystallization of binary systems where a low molar mass polyethylene oligomer was blended with polypropylene and polyethylene resins. It was found that the polyethylene oligomer was easily incorporated into the selected polyolefins thanks to rapid molecular diffusion and good miscibility in the molten state. However, it appeared that the blends underwent solid-liquid phase separation upon crystallization, leading to biphasic materials in the solid state. In a second part, a reactive system consisting of two functional oligomers was studied as a new strategy for the compatibilization of immiscible polyethylene/polyamide blends. Despite the interesting morphologies and properties observed, it was concluded that the use of such a reactive system did not result in efficient compatibilization compared to commonly used compatibilizer precursors. Lastly, polyethylene oligomers with various functionalities were investigated as interface agents in glass fibre-reinforced polyethylene, with the aim of improving both processability and mechanical properties. It was demonstrated that polyethylene oligomers with adequate functional groups could be successfully used as dispersants by reducing interparticle interactions during melt processing as well as coupling agents improving matrix-filler interfacial adhesion in the solid state

Spinodal decomposition is a phase separation mechanism within the miscibility gap. Its importance in case of Fe-Cr system, the basis of the whole stainless steel family, stems from a phenomenon known as the “475oC embrittlement” which results in a ruin of mechanical properties of ferritic, martensitic and duplex stainless steels. This work is aimed at a better understanding of the phase separation process in   the Fe-Cr system. Alloys of 10 to 55 wt.% Cr , each five percent, were homogenized to achieve fully ferritic microstructure and then isothermally aged at 400, 500 and 600oC for different periods of time ranging from 30min to 1500 hours. Hardness of both homogenized and aged samples were measured by the Vickers micro-hardness method and then selected samples were studied by means of Transmission Electron Microscopy (TEM).  It was observed that hardness of homogenized samples increased monotonically with increasing Cr content up to 55 wt.% which can be attributed to solution hardening as well as higher hardness of pure chromium compared to pure iron.  At 400oC no significant change in hardness was detected for aging up to 1500h, therefore we believe that phase separation effects at 400oC are very small up to this time. Sluggish kinetics is imputed to lower diffusion rate at lower temperatures. At 500oC even after 10h a noticeable change in hardness, for alloys containing 25 wt.% Cr and higher, was observed which indicates occurrence of phase separation. The alloy with 10 wt.% Cr did not show change in hardness up to 200h which suggests that this composition falls outside the miscibility gap at 500oC. For compositions of 15 and 20 wt.% Cr only a small increase in hardness was detected even after 200h of aging at 500oC, which could be due to the small amounts of α´ formed. However, it means that alloys of 15 wt.% Cr and higher are suffering phase separation. For compositions inside the miscibility gap, hardening effect is a result of phase separation either by nucleation and growth or spinodal decomposition. To distinguish between these two mechanisms, TEM studies were performed and we found evidence that at 500oC the Fe-25 wt.% Cr sample decomposes by nucleation  and growth  while that of 35 wt.% Cr  shows characteristics of the spinodal mechanism. For compositions inside the miscibility gap, with increasing Cr content up to 40% the change in hardness generally increased and for 45% and higher it always decreased. This suggests that the composition range corresponding to the spinodal region at 500oC is biased towards the Fe-rich side of the phase diagram. At 600oC only samples of 25, 30 and 35 wt.% Cr were studied because according to the previous studies, the spinodal boundary is most probably located in this composition range. However, no change in hardness was observed even up to 24h. We believe that this means the miscibility line lies below 600oC for alloys containing 35 wt.% Cr and lower. Further investigations are needed to confirm and explain this result.

No description available.

L’électrofilage est un procédé permettant de préparer des fibres possédant un diamètre de l’ordre du micromètre ou de quelques centaines de nanomètres. Son utilisation est toutefois limitée par le manque de contrôle sur la structure et les propriétés des fibres ainsi produites. Dans ce travail, des fibres électrofilées à partir de mélanges de polystyrène (PS) et de poly(vinyl méthyl éther) (PVME) ont été caractérisées. La calorimétrie différentielle à balayage (DSC) a montré que les fibres du mélange PS/PVME sont miscibles (une seule transition vitreuse) lorsque préparées dans le benzène, alors qu'une séparation de phases a lieu lorsque le chloroforme est utilisé. Les fibres immiscibles sont néanmoins malléables, contrairement à un film préparé par évaporation du chloroforme qui a des propriétés mécaniques médiocres. Des clichés en microscopies optique et électronique à balayage (MEB) ont permis d’étudier l'effet de la composition et du solvant sur le diamètre et la morphologie des fibres. Des mesures d’angles de contact ont permis d’évaluer l’hydrophobicité des fibres, qui diminue avec l’ajout de PVME (hydrophile); les valeurs sont de 60° supérieures à celles des films de composition équivalente. Un retrait sélectif du PVME a été réalisé par l’immersion des fibres dans l’eau. La spectroscopie infrarouge a montré que la composition passe de 70 à 95% de PS pour une fibre immiscible mais seulement à 75% pour une fibre miscible. Ces résultats indiquent que la phase riche en PVME se situe presque uniquement à la surface des fibres immiscibles, ce qui a été confirmé par microscopie à force atomique (AFM) et MEB. Finalement, l’effet du mélange des deux solvants, lors de l’électrofilage du mélange PS/PVME, a été étudié. La présence du chloroforme, même en quantité réduite, provoque une séparation de phases similaire à celle observée avec ce solvant pur. / Electrospinning is a simple method for the preparation of polymer fibers with diameters of hundreds of nanometers to a few micrometers. Although it is a versatile method, some issues remain in the control of the structure and properties of electrospun fibers. In this study, fibers electrospun from polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends were characterized. Differential scanning calorimetry (DSC) revealed that fibers electrospun from benzene are miscible while a phase separation occurs when the fibers are electrospun from chloroform. While films cast from chloroform show poor mechanical properties, immiscible fibers are ductile. The effects of the blend composition and the solvent on the fiber diameter and morphology were observed by scanning electron microscopy (SEM) and optical microscopy. Afterwards, contact angle measurements were made to evaluate the hydrophobicity of the fibers which decreases as hydrophilic PVME is added to the blend; the values for the fibers were found to be 60° higher than their equivalent in films. PVME was selectively removed from the immiscible fibers by complete immersion into water. Infrared spectroscopy revealed that this process increases the PS content from 70 to 95% for immiscible fibers but only to 75% for miscible fibers. These results show that the PVME-rich phase is almost completely distributed on the fiber surface, which was confirmed by atomic force microscopy (AFM) and SEM. Finally, the electrospinning of PS/PVME blends from chloroform/benzene solutions was studied. The presence of chloroform, even as a residual amount, causes a phase separation just as it does in fibers electrospun from pure chloroform.