Nous étudions numériquement la solidification directionnelle d'un alliage binaire à base de succinonitrile. Pour cela, nous développons un code s'appuyant sur le formalisme du champ de phase adapté au cas de la croissance dans des lames minces. Les résultats numériques obtenus sont comparés qualitativement et quantitativement avec les observations expérimentales. Une bonne confirmation des lois expérimentales et de nouvelles informations sur la dynamique des microstructures sont obtenues.La direction de croissance est généralement limitée par deux axes : l'axe cristallin principal et la direction du gradient thermique. Une première partie de la thèse porte sur l'étude des effets de la désorientation de l'axe cristallin sur la direction de croissance des structures et sur leurs morphologies. Nos résultats sont directement comparés à la loi expérimentale qui donne la réponse en orientation des microstructures sur l'ensemble de leur domaine d'existence en fonction du nombre de Péclet. Nous obtenons un accord très satisfaisant entre simulation et expérience. Dans la seconde partie de la thèse, une instabilité oscillante (mode 2λ − O) est étudiée en se basant sur le diagramme de stabilité expérimental. Dans ce mode deux cellules voisines oscillent en opposition de phase en largeur et en hauteur. Nos simulations reproduisent ce mode oscillant dans des lames minces et permettent une comparaison quantitative avec les expériences. Le régime des oscillations forcées est notamment exploré pour obtenir des informations sur la réponse en fréquence du système. / We report on a numerical study of directional solidification in thin samples of succinonitrile-based dilute alloy. This thesis is based on 3D phase-field simulations. Numerical results are compared qualitatively and quantitatively with experimental observations. The comparison gives a good confirmation of the experimental laws, while providing new information on the dynamics of microstructures. Growth direction of the microstructure is constrained by two axes : the main crystal axis and the direction of the thermal gradient. Simulations allow us to test the variations of the growth direction and the microstructure stability at various misorientation angles. Our results are directly compared with the experimental law that gives the microstructure orientation response in a large domain of Péclet numbers. We obtain a good agreement, both on qualitative and quantitative grounds, between experiments and 3D simulations.In the second part of this manuscript, an oscillatory instability (2λ − O mode) is numerically studied. This mode involves oscillations of both cell width and cell tip position. This instability is reproduced in numerical simulations with the aim of allowing a fine and relevant comparison with experiments of the domain of existence and the periods of oscillation. In particular, the forced oscillation regime is explored to obtain information on the frequency response of the system.

Com o objetivo do entendimento do modo pelo qual são formadas as diferentes morfologias dos óxidos de lantanídeos obtidos a partir da calcinação de citratos, neste trabalho foram sintetizados óxidos de lantanídeos (La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3 e Eu2O3) a partir da calcinação dos respectivos citratos. Durante a síntese da série dos sais [LnCit.xH2O], uma nova série de sais com a composição [Ln2(HCit)3.2H2O] foi isolada e caracterizada para (Ln = La, Ce, Pr, Nd, Sm, Eu). Em contraste com os sais amorfos [LnCit.xH2O] configurando agregados irregulares, os sais [Ln2(HCit)3.2H2O] são cristalinos com hábitos cristalinos fibrosos. Os estudos térmicos destes sais mostraram perfis distintos de decomposição térmica em atmosfera de ar. A decomposição da espécie amorfa fornece itaconatos de lantanídeos, seguido pela formação do oxicarbonato de lantanídeo e finalmente o respectivo óxido. A espécie cristalina, por sua vez, se decompõe, formando oxalato de lantanídeos seguido pela formação de oxicarbonato e posteriormente óxido. A morfologia dos óxidos de lantanídeos foi investigada utilizando microscopia eletrônica de varredura. Esta técnica mostrou a correlação entre as morfologias dos óxidos e as dos respectivos precursores obtidos a partir da calcinação dos diferentes citratos. Enquanto a calcinação dos sais amorfos formado por partículas irregularmente formadas resultou em óxidos com partículas irregulares, a calcinação dos citratos cristalinos, com partículas fibrosas, resultou na formação de óxidos com partículas fibrosas. Isso sugere fortemente que a morfologia dos precursores age como molde na formação dos óxidos dando origem a partículas com morfologias hierarquicamente similares. Foram conduzidos testes catalíticos de ozonização de fenol em meio ácido utilizando, as diferentes morfologias do CeO2. Todos os tipos morfológicos do CeO2 mostraram excelente atividade, proporcionando taxas de mineralização de aproximadamente 100%, contra 60% da ozonização na ausência de catalisador. O óxido tipo 2, proveniente do precursor [Ce2(HCit)3.2H2O] mostrou a mais alta ela foi de 5,1 unidade de (Kcorr / min-1.m-2.10-3) atividade. As diferentes atividades aprtesentadas pelas diferentes morfologias dos óxidos foram atribuídas às quantidades de Ce(III) como centro ativo na superfície os óxidos. Estas diferentes quantidades de Ce (III), estimadas por luminescência óptica e o Uv/Vis, foram atribuídas aos diferentes teores de carbono nos precursores que competem pelo oxigênio durante a calcinação. Isso leva à estabilização de Ce(III) e vacâncias de oxigênio na superfície dos óxidos. / With the aim of understanding the way that the morphologies of lanthanide oxides are influenced by precursors two series of lanthanide citrates were synthesized, characterized and used as precursors in the synthesis of these oxides through calcinations (La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3 and Eu2O3) . A new series of lanthanide citrates with formula [Ln2(HCit)3.2H2O] was synthesized and characterized. Compared to amorphous [LnCit.xH2O], these new salts have a fibrous morphology pointed out by SEM analysis. Thermal analysis show that [LnCit.xH2O] decompose through two major steps: itaconates, oxycarbonates and finally lanthanide oxides. [Ln2(HCit)3.2H2O], on the other hand, decompose through two distinct steps: oxalates, oxycarbonates and lanthanide oxides. The morphology of lanthanide oxides was investigated using scanning electron microscopy. A correlation between the morphologies of the oxides and their precursors could be found. While amorphous citrates consisting of irregular shaped particles give rise to irregular shaped oxides particles, calcinations of fibrous crystalline salts series led to fibrous crystalline oxide shaped particles. These results strongly suggest that the morphology of a citrate polymeric precursor acts as a template, producing to hierarchically similar particles. Acid catalytic ozonation of phenol using three morphologies of CeO2 were carried out. All tested oxides show high activity providing 100% of mineralization of phenol, whereas without catalyst only 60% of mineralization was observed. The oxide synthesized from [Ce2(HCit)3.2H2O] shows the higher activity per surface area. CeO2 synthesized from [CeCit.xH2O] shows intermediary activity per surface area. The internal combustion synthesized CeO2 showed the worst activity. The different activities showed by the three morphological forms of CeO2 were attributed to the presence of different Ce(III) amounts in the surface of catalysts. The quantities of Ce(III) were estimated by luminescence and the results agreed very well with the activity of catalysts. The different Ce(III) contents in the precursors were attributed to different carbon contents in the precursor, which compet for oxygen of environment during calcinations, leading to stabilization of Ce(III) and vacancies in the oxides.

Com o objetivo do entendimento do modo pelo qual são formadas as diferentes morfologias dos óxidos de lantanídeos obtidos a partir da calcinação de citratos, neste trabalho foram sintetizados óxidos de lantanídeos (La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3 e Eu2O3) a partir da calcinação dos respectivos citratos. Durante a síntese da série dos sais [LnCit.xH2O], uma nova série de sais com a composição [Ln2(HCit)3.2H2O] foi isolada e caracterizada para (Ln = La, Ce, Pr, Nd, Sm, Eu). Em contraste com os sais amorfos [LnCit.xH2O] configurando agregados irregulares, os sais [Ln2(HCit)3.2H2O] são cristalinos com hábitos cristalinos fibrosos. Os estudos térmicos destes sais mostraram perfis distintos de decomposição térmica em atmosfera de ar. A decomposição da espécie amorfa fornece itaconatos de lantanídeos, seguido pela formação do oxicarbonato de lantanídeo e finalmente o respectivo óxido. A espécie cristalina, por sua vez, se decompõe, formando oxalato de lantanídeos seguido pela formação de oxicarbonato e posteriormente óxido. A morfologia dos óxidos de lantanídeos foi investigada utilizando microscopia eletrônica de varredura. Esta técnica mostrou a correlação entre as morfologias dos óxidos e as dos respectivos precursores obtidos a partir da calcinação dos diferentes citratos. Enquanto a calcinação dos sais amorfos formado por partículas irregularmente formadas resultou em óxidos com partículas irregulares, a calcinação dos citratos cristalinos, com partículas fibrosas, resultou na formação de óxidos com partículas fibrosas. Isso sugere fortemente que a morfologia dos precursores age como molde na formação dos óxidos dando origem a partículas com morfologias hierarquicamente similares. Foram conduzidos testes catalíticos de ozonização de fenol em meio ácido utilizando, as diferentes morfologias do CeO2. Todos os tipos morfológicos do CeO2 mostraram excelente atividade, proporcionando taxas de mineralização de aproximadamente 100%, contra 60% da ozonização na ausência de catalisador. O óxido tipo 2, proveniente do precursor [Ce2(HCit)3.2H2O] mostrou a mais alta ela foi de 5,1 unidade de (Kcorr / min-1.m-2.10-3) atividade. As diferentes atividades aprtesentadas pelas diferentes morfologias dos óxidos foram atribuídas às quantidades de Ce(III) como centro ativo na superfície os óxidos. Estas diferentes quantidades de Ce (III), estimadas por luminescência óptica e o Uv/Vis, foram atribuídas aos diferentes teores de carbono nos precursores que competem pelo oxigênio durante a calcinação. Isso leva à estabilização de Ce(III) e vacâncias de oxigênio na superfície dos óxidos. / With the aim of understanding the way that the morphologies of lanthanide oxides are influenced by precursors two series of lanthanide citrates were synthesized, characterized and used as precursors in the synthesis of these oxides through calcinations (La2O3, CeO2, Pr6O11, Nd2O3, Sm2O3 and Eu2O3) . A new series of lanthanide citrates with formula [Ln2(HCit)3.2H2O] was synthesized and characterized. Compared to amorphous [LnCit.xH2O], these new salts have a fibrous morphology pointed out by SEM analysis. Thermal analysis show that [LnCit.xH2O] decompose through two major steps: itaconates, oxycarbonates and finally lanthanide oxides. [Ln2(HCit)3.2H2O], on the other hand, decompose through two distinct steps: oxalates, oxycarbonates and lanthanide oxides. The morphology of lanthanide oxides was investigated using scanning electron microscopy. A correlation between the morphologies of the oxides and their precursors could be found. While amorphous citrates consisting of irregular shaped particles give rise to irregular shaped oxides particles, calcinations of fibrous crystalline salts series led to fibrous crystalline oxide shaped particles. These results strongly suggest that the morphology of a citrate polymeric precursor acts as a template, producing to hierarchically similar particles. Acid catalytic ozonation of phenol using three morphologies of CeO2 were carried out. All tested oxides show high activity providing 100% of mineralization of phenol, whereas without catalyst only 60% of mineralization was observed. The oxide synthesized from [Ce2(HCit)3.2H2O] shows the higher activity per surface area. CeO2 synthesized from [CeCit.xH2O] shows intermediary activity per surface area. The internal combustion synthesized CeO2 showed the worst activity. The different activities showed by the three morphological forms of CeO2 were attributed to the presence of different Ce(III) amounts in the surface of catalysts. The quantities of Ce(III) were estimated by luminescence and the results agreed very well with the activity of catalysts. The different Ce(III) contents in the precursors were attributed to different carbon contents in the precursor, which compet for oxygen of environment during calcinations, leading to stabilization of Ce(III) and vacancies in the oxides.

La présence de matières plastiques dans les DEEE (déchets des équipements électriques et électroniques) a augmenté de 25% ces cinq dernières années. Avec la mise en place de nouvelles réglementations imposant des objectifs de recyclage élevés et l’augmentation des cours du pétrole, le recyclage des matières plastiques devient plus que jamais d’actualité. Dans ce contexte, tout en travaillant avec des polymères vierges, l’objectif de ce travail est de trouver une voie de valorisation des DEEE par le mélange de polymères. Le travail s’est focalisé sur l’amélioration des propriétés mécaniques des mélanges ABS/PC (70%/30% en masse) en structurant la morphologie de mélanges sous formes allongées (fibres et/ou lamelles). Pour ce faire, des outils spécifiques novateurs (éléments multiplicateurs de couches, filière de coextrusion fibrillaire) sont développés et utilisés. La démarche consiste à structurer d’abord des joncs, qui sont ensuite granulés, puis injectés lors d’une deuxième étape pour fabriquer des éprouvettes. Lorsque des morphologies allongées sont obtenues, des améliorations notables de propriétés (au choc en particulier) sont observées. Le travail termine par l’étude de l’effet sur la structuration et les propriétés finales d’un compatibilisant, l’ABS greffé anhydride maléique, synthétisé par extrusion réactive et rajouté au mélange ABS/PC. / Plastics in WEEE (Waste of Electric and Electronic Equipments) have increased up to 25% in the last five years. As new regulations are setting up increased recycling objectives and the oil prize is also increasing, plastic recycling is more than never an issue. In this context, while still working on virgin polymers, this work objective is to find a way to valorize the WEEE by the use of polymer blends. This work is focused on the upgrading of mechanical properties of ABS/PC (70%/30% wt%) blends by structuring the morphology of the blends creating elongated shapes (fibers and/or lamellas). To do so, innovative specific tools have been developed and used such as layer-multiplying mixing elements or fibrillar coextrusion dye. The first step of the procedure is to create structured strands of polymers which are then pelletized. Then these pellets are injected in a second step to create specimens. When elongated morphologies are obtained, significant improvements are observed in properties, especially for impact behavior. Finally, this work studies the effect of a compatibilizer on the structuration and the final properties of the blends. The compatibilizer, maleic anhydride grafted ABS, was synthesized through reactive extrusion and added in ABS/PC blends.

La présence de matières plastiques dans les DEEE (déchets des équipements électriques et électroniques) a augmenté de 25% ces cinq dernières années. Avec la mise en place de nouvelles réglementations imposant des objectifs de recyclage élevés et l’augmentation des cours du pétrole, le recyclage des matières plastiques devient plus que jamais d’actualité. Dans ce contexte, tout en travaillant avec des polymères vierges, l’objectif de ce travail est de trouver une voie de valorisation des DEEE par le mélange de polymères. Le travail s’est focalisé sur l’amélioration des propriétés mécaniques des mélanges ABS/PC (70%/30% en masse) en structurant la morphologie de mélanges sous formes allongées (fibres et/ou lamelles). Pour ce faire, des outils spécifiques novateurs (éléments multiplicateurs de couches, filière de coextrusion fibrillaire) sont développés et utilisés. La démarche consiste à structurer d’abord des joncs, qui sont ensuite granulés, puis injectés lors d’une deuxième étape pour fabriquer des éprouvettes. Lorsque des morphologies allongées sont obtenues, des améliorations notables de propriétés (au choc en particulier) sont observées. Le travail termine par l’étude de l’effet sur la structuration et les propriétés finales d’un compatibilisant, l’ABS greffé anhydride maléique, synthétisé par extrusion réactive et rajouté au mélange ABS/PC. / Plastics in WEEE (Waste of Electric and Electronic Equipments) have increased up to 25% in the last five years. As new regulations are setting up increased recycling objectives and the oil prize is also increasing, plastic recycling is more than never an issue. In this context, while still working on virgin polymers, this work objective is to find a way to valorize the WEEE by the use of polymer blends. This work is focused on the upgrading of mechanical properties of ABS/PC (70%/30% wt%) blends by structuring the morphology of the blends creating elongated shapes (fibers and/or lamellas). To do so, innovative specific tools have been developed and used such as layer-multiplying mixing elements or fibrillar coextrusion dye. The first step of the procedure is to create structured strands of polymers which are then pelletized. Then these pellets are injected in a second step to create specimens. When elongated morphologies are obtained, significant improvements are observed in properties, especially for impact behavior. Finally, this work studies the effect of a compatibilizer on the structuration and the final properties of the blends. The compatibilizer, maleic anhydride grafted ABS, was synthesized through reactive extrusion and added in ABS/PC blends.

L'attractivité des matériaux polymères issus de ressources renouvelables augmente continuellement en raison de la prise de conscience environnementale de la société. Dans ce contexte, l’acide polylactique (PLA) est un biopolymère qui possède d’indéniables atouts (notamment en termes de rigidité et résistance en traction/flexion) permettant d’envisager des applications à grande échelle, par exemple pour l’automobile. Cependant, les applications durables du PLA sont encore considérablement restreintes à cause de sa fragilité et de sa stabilité thermique limitée. Dans cette thèse, nous nous sommes focalisés sur la conception de nouveaux matériaux à base de PLA pour des applications dans l’automobile, en travaillant notamment sur l’amélioration des propriétés thermiques et mécaniques (notamment la ductilité), y compris sous haute vitesse de déformation. Ainsi, la composition optimale permettant d’atteindre le meilleur compromis entre différentes propriétés (ductilité, résistance et rigidité, résilience, stabilité thermique…), tout en étant composée d’au moins 50% de matériaux biosourcés est déterminée. D'autres stratégies visant à améliorer la capacité ou la vitesse de cristallisation des compositions à base de PLA ont également été étudiées. Dans tous ces développements, une attention particulière est portée sur l’étude des interactions entre structure, propriétés et process. / The interest to use polymeric materials derived from renewable resources increases continuously due to considerably improved environmental awareness and the expected depletion of petrochemical ressources. In this regard, Poly(lactic acid), PLA, is a biopolymer that can respond to the demand for such materials for a wide range of applications, thanks to interesting mechanical properties such as high tensile/flexural strength and rigidity, in particular. However, in many cases, durable applications of PLA have been significantly limited by its inherent brittleness and limited thermal stability. In this dissertation, we focused on the design of new biobased PLA materials for automotive parts subjected to severe loading and environmental conditions, by improving thermal and mechanical properties, including under high strain rate loadings. Thus, the most promising compound is selected as the one that offers the best balance between different properties (ductility, strength and stiffness, impact toughness, good thermal stability…) with a content of bio-sourced polymer in the blend at least equal to 50%. Other strategies to improve crystallinity of PLA-based compounds are also studied. In all those developments, a particular attention is paid to the study of structure-process-properties interactions.

We present a mean field model for a mixture of AB diblock-copolymers and A-block selective nanoparticles confined between two identical non-selective walls. A horizontally symmetric lamellar structure of the nanocomposite is considered where nanoparticles are allowed to segregate between the polymer–wall interfaces. For a fixed value of wall separation, we study changes in the free energy as a function of the number of lamellar layers and the amount of nanoparticle uptake in the A-phase denoted by y = ϕx with 0 ≤ x ≤ 1 for a given value of ϕ, where ϕ is the overall nanoparticle volume fraction. The absorption isotherm for nanoparticle uptake in the A-phase as a function of ϕ shows saturation beyond a threshold value ϕs, and the optimal value of uptake y increases with increasing strength of monomer–nanoparticle attractive interaction. Increasing ϕ above ϕs produces a decrease in the optimal number of lamellar layers which is related to a jump-like transition of the chain extension. The effect of varying film thickness is also studied. By considering A-block selective walls we also investigated a wetting transition of the copolymer film and found the transition to be discontinuous. A corresponding phase diagram is constructed. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

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No description available.

This thesis is a study of the morphology and sediment transport dynamics of mountain streams in southeast Australia. Mountain streams represent important geomorphological and ecological systems in Australia which have hitherto been poorly studied. The variability of mountain stream reach morphology was investigated at the regional scale using topographical surveys and sediment sampling techniques. Study sites were stratified by slope and local lithology. Eight channel-morphologies including Bedrock, Cascade, Step-pool, Planebed, Pool-Riffle, Cascade-pool, Riffle-step and Infilled, were identified using an objective statistical approach. Overall, channel types were found to correspond to existing reach-scale mountain stream templates. Five morphologies were associated with a specific lithology type which controlled the size and shape of grains supplied to the channels. Differences in coarse sediment transport processes between morphologies were investigated using stream monitoring techniques and Optically Stimulated Luminescence (OSL) dating. Monitoring results from a 3 year period indicated that channel beds are resistant to entrainment with shear stress thresholds for bedload transport ranging between 64 to 74 N/m2. Transport of reach median grain sizes requires floods that exceed bankfull discharge. Existing competence equations were found to over-predict the hydraulic driving force and consequently, a modified entrainment model was used to account for the regional channel characteristics. OSL dating was investigated as a tool to provide data on long-term sediment transport processes. Minimum age model results from the OSL dates show overall agreement with a selected entrainment model, and indicate differences in sediment transport dynamics between some reach morphology types. A regime model was used to quantify the physical domains of different channel morphologies. Limitations of the model were overcome by modifying the sediment supply surrogate to better reflect the dominant transported bedload size. Morphology types were delineated according to different sediment transport capacity-sediment supply domains. The distribution of channel morphology types within a series of catchments in southeast Australia was modelled within a GIS platform using the diagnostics of reach morphology derived from this study. The model provides a conceptual framework to evaluate the potential link between channel form, potential habitat diversity and aquatic biodiversity within the channel network in mountain streams.