Polymer nanocomposites (PNCs) are hybrid materials incorporating organic or inorganic nanoparticles (NPs) with at least one dimension in the submicron scale. Over the last two decades, these materials have drawn a remarkable attention due to their central role in industrial formulations and technological applications, extending from food packaging to smart coatings. Incorporating nanoparticles (NPs) to a polymer matrix can significantly alter the conformation and the mobility of the polymer chains in their proximity. Moreover, understanding the delicate balance between the enthalpic and entropic interactions is crucial to control and predict the ability of NPs to diffuse and disperse in the polymer matrix. The impact of these interactions on the structure and the dynamics of polymer chains and NPs is fully revealed in how a number of macroscopic properties changes, justifying the high interest on these materials for industrial applications. In this thesis, the impact on the structure, dynamics, viscosity and thermal conductivity of a number of microscopic properties is investigated by performing Molecular Dynamics (MD) simulations. Specifically, the PNC is represented by a coarse-grained model of a melt of linear homopolymer chains containing spherical NPs. Throughout this work, a number of parameters are modified in order to unveil possible patterns in the PNC’s performance. To this end, this work focuses on the consequences of modifying the NP size dispersity, NP-polymer chain relative size, and chains’ degree of stiffness. Four theoretical models describing the diffusivity of NPs, three of which include nano-scale corrections, have been averaged to study the dependence of dilute NPs’ diffusivity on the NP polydispersity index. By comparing these models to the simulation results at different degrees of polydispersity, it is possible to obtain a more complete picture of their validity as compared to the monodisperse case. Regarding the diffusion of polymer chains, simulation results were in good agreement with the experimental results previously obtained by Composto and coworkers (Soft Matter 2012, 8, 6512), which relate the chains’ diffusivity to the average interparticle distance. As far as the transport properties are concerned, they show a weaker dependence on the polydispersity index. By contrast, results on viscosity and thermal conducitivity show that they are conditioned by the polymer-NP specific interfacial area and the inverse average mass, respectively. These results are in good agreement with previous experimental results. A deeper examination of this intriguing deviation from viscosity predictions in traditional composites, reveals a non-trivial combination of thickening and thinning effects contributing to the final viscosity of the PNC. This thesis also address the influence of the chains’ stiffness on the dynamical and viscous behaviour. An isotropic-to-nematic phase transition is observed, regardless of the NP-monomer interactions, below which a monotonic increase of both properties is observed, whereas orientationally ordered systems dramatically modify them, resulting into a steep increase or a smooth decrease depending on the direction in which they are measured.

Metilaluminoxano, trietilalumínio e trimetilalumínio foram encapsulados em uma rede de sílica usando sol-gel não hidrolítico. Óxidos mistos foram produzidos através da combinação dos precursores da sílica com Mg(OEt)2, MgCl2 e MgCl2 .6H2O. Os xerogéis resultantes foram caracterizados por uma série de técnicas para determinar os elementos, estrutura, textura e características morfológicas dos cocatalisadores encapsulados. A natureza do cocatalisador afeta o tempo de geleificação. A quantidade de cocatalisador encapsulado não parece ser afetada pelo volume do alquilalumínio, mas a rede de sílica e a organização do xerogel foram, de acordo com os resultados do infravermelho e XRD. Uma forte redução da área específica ocorre comparando os sistemas encapsulados com as sílicas sintetizadas em condições semelhantes. Os alquilalumínios encapsulados foram avaliados na polimerização de eteno usando Cp2ZrCl2 como catalisador na presença e ausência de MAO externo. Os cocatalisadores encapsulados não foram ativos em uma relação Al/Zr de 250 a 500. Para os sistemas mistos combinando MAO homogêneo (externo) com MAO encapsulado, a adição do cocatalisador encapsulado parece não afetar a atividade catalítica. O peso molecular dos polímeros obtido usando catalisador encapsulado é inferior ao obtido a partir das reações homogêneas. No entanto, a polidispersão obtida nos polímeros usando cocatalisador encapsulado foi maior que a obtida a partir de sistemas homogêneos e impregnado. / Methylaluminoxane, tetraethylaluminum and trimethylaluminum were encapsulated within a silica-based material using a non-hydrolytic sol-gel process. Mixed oxides were also produced by combining silica precursors with Mg(OEt)2, MgCl2 and MgCl2 .6H2O. The resulting xerogels were characterized by a series of complementary techniques to determine the elemental, the structural, the textural and the morphological characteristics of the encapsulated cocatalysts. The nature of the alkyl aluminum strongly affects the gelification time. The amount of encapsulated cocatalyst did not appear to be affected by the alkylaluminum volume, but the silica network and the xerogel organization were, according to infrared and X-ray diffraction measurements. There was a large surface reduction for the encapsulated systems compared with the silica that was synthesized under the same conditions. The resulting supported alkylaluminum was evaluated in the polymerization of ethylene using Cp2ZrCl2 as the catalyst in the presence and the absence of external MAO. The encapsulated cocatalysts were not shown to be active in the Al/Zr range of 250-500. For the mixed systems that combined homogeneous MAO with encapsulated MAO, the addition of the encapsulated cocatalyst did not appear to affect the catalyst activity. The molecular weight of the polymers that were obtained by using the encapsulated cocatalyst was lower than the molecular weight of the polymers that were obtained by using the homogeneous catalyst. Nevertheless, the polydispersity of the polymers that were obtained in the presence of the encapsulated cocatalyst was greater than polydispersity of the polymers that were produced with the homogeneous catalyst or the impregnated MAO.

Metilaluminoxano, trietilalumínio e trimetilalumínio foram encapsulados em uma rede de sílica usando sol-gel não hidrolítico. Óxidos mistos foram produzidos através da combinação dos precursores da sílica com Mg(OEt)2, MgCl2 e MgCl2 .6H2O. Os xerogéis resultantes foram caracterizados por uma série de técnicas para determinar os elementos, estrutura, textura e características morfológicas dos cocatalisadores encapsulados. A natureza do cocatalisador afeta o tempo de geleificação. A quantidade de cocatalisador encapsulado não parece ser afetada pelo volume do alquilalumínio, mas a rede de sílica e a organização do xerogel foram, de acordo com os resultados do infravermelho e XRD. Uma forte redução da área específica ocorre comparando os sistemas encapsulados com as sílicas sintetizadas em condições semelhantes. Os alquilalumínios encapsulados foram avaliados na polimerização de eteno usando Cp2ZrCl2 como catalisador na presença e ausência de MAO externo. Os cocatalisadores encapsulados não foram ativos em uma relação Al/Zr de 250 a 500. Para os sistemas mistos combinando MAO homogêneo (externo) com MAO encapsulado, a adição do cocatalisador encapsulado parece não afetar a atividade catalítica. O peso molecular dos polímeros obtido usando catalisador encapsulado é inferior ao obtido a partir das reações homogêneas. No entanto, a polidispersão obtida nos polímeros usando cocatalisador encapsulado foi maior que a obtida a partir de sistemas homogêneos e impregnado. / Methylaluminoxane, tetraethylaluminum and trimethylaluminum were encapsulated within a silica-based material using a non-hydrolytic sol-gel process. Mixed oxides were also produced by combining silica precursors with Mg(OEt)2, MgCl2 and MgCl2 .6H2O. The resulting xerogels were characterized by a series of complementary techniques to determine the elemental, the structural, the textural and the morphological characteristics of the encapsulated cocatalysts. The nature of the alkyl aluminum strongly affects the gelification time. The amount of encapsulated cocatalyst did not appear to be affected by the alkylaluminum volume, but the silica network and the xerogel organization were, according to infrared and X-ray diffraction measurements. There was a large surface reduction for the encapsulated systems compared with the silica that was synthesized under the same conditions. The resulting supported alkylaluminum was evaluated in the polymerization of ethylene using Cp2ZrCl2 as the catalyst in the presence and the absence of external MAO. The encapsulated cocatalysts were not shown to be active in the Al/Zr range of 250-500. For the mixed systems that combined homogeneous MAO with encapsulated MAO, the addition of the encapsulated cocatalyst did not appear to affect the catalyst activity. The molecular weight of the polymers that were obtained by using the encapsulated cocatalyst was lower than the molecular weight of the polymers that were obtained by using the homogeneous catalyst. Nevertheless, the polydispersity of the polymers that were obtained in the presence of the encapsulated cocatalyst was greater than polydispersity of the polymers that were produced with the homogeneous catalyst or the impregnated MAO.

Rheological properties of idealised models which exhibit all the non-Newtonian flow phenomenology commonly seen in dense suspensions are investigated by particulate-dynamics computer-simulations. The objectives of these investigations are: (i) to establish the origins of various aspects of dense suspension rheology such as shear-thinning, shear thickening and dilatancy; (ii) to elucidate the different regions of a typical dense suspension rheogram by examining underlying structures and shear induced anisotropies in kinetic energy, diffusivity and pressure; (iii) to investigate the scaling of the simplest idealised model suspension; i.e. the hard-sphere model in Newtonian media and its relationship to the isokinetic flow curves obtained through non-equilibrium molecular dynamics (NEMD) simulations; (iv) to preliminarily determine the effect of perturbations present in all real colloidal suspensions, namely particle size polydispersity and a slight 'softness' of the interparticle potential. Non-equilibrium isokinetic simulations have been performed upon ;systems of particles interacting through the classical hard-sphere potential and a perturbation thereof, in which the hard-core is surrounded by a 'slightly soft' repulsive skin. The decision to base the present work upon isokinetic studies was made in order to obtain a better under- standing of suspension rheology by making a direct connection with previous NEMD studies of thermal systemst(93). These studies have shown that the non-linear behaviour exhibited by these systems under shear is atttributable to a shear-induced perturbation of the equilibrium phase behaviour. The present study shows this behaviour to correspond to the high shear region of the generalised suspension flow curve. / Science and Engineering Research Council and Unilever Research

No description available.

Au cours de ce travail, nous nous sommes attachés à prédire les caractéristiques rhéologiques de suspensions de particules dans des situations non newtoniennes. Nous avons tout d'abord étudié expérimentalement le comportement rhéologique de suspensions bidisperses de particules non colloïdales et non browniennes immergées dans un fluide à seuil dans les situations où les interactions entre particules sont hydrodynamiques (mécaniques). Nous avons montré que l'influence de la polydispersité des particules sur le module élastique et le seuil de contrainte de la suspension pouvait être décrit en utilisant un modèle d'empilement développé pour les matériaux granulaires secs. Deux relations analytiques simples permettant d'estimer le module élastique et la contrainte seuil d'une suspension non newtonienne polydisperse en fonction des caractéristiques des constituants ont alors été proposées et validées. Nous nous sommes ensuite intéressés à la prédiction des caractéristiques globales de suspensions contenant une forte concentration de particules de taille différente dans le cadre d'une approche par changement d'échelle. Pour cela, nous avons mis en uvre une approche par motifs morphologiques permettant la prise en compte de paramètres géométriques tels que la distribution de tailles des inclusions ou les distances entre particules voisines. Les résultats de ce modèle ont été validés par comparaison avec des données expérimentales de la littérature. Nous avons ensuite montré que les modèles morphologiques permettaient également de décrire l'évolution des modules complexes d'un matériau thixotrope subissant une transition de phase liquide-solide due à la croissance et la percolation d'un réseau de particules attractives. Dans la dernière partie de cette étude, nous avons étudié expérimentalement l'influence de l'histoire de cisaillement sur la structuration et la déstructuration d'une suspension colloïdale thixotrope / In this work, we aimed to predict the rheological properties of suspensions of particles in non-Newtonian fluids. We first studied experimentally the rheological behaviour of bidisperse suspensions of non colloidal particles and non-Brownian immersed in a yield stress fluid in situations where interactions between particles are hydrodynamic (mechanical). We showed that the influence of the polydispersity on the elastic modulus and yield stress of the suspension could be described using a packing model developed for dry granular materials.Two simple closed form estimates for both the elastic modulus and the yield stress of non-Newtonian polydisperse suspension as a function of the characteristics of the constituents were proposed and validated. This study was then extended in a micromechanical analytical framework to predict the macroscopic characteristics of suspensions containing highly concentration of particles with different size. Our ne w model, called a "Morphologically Representative Pattern - Based Approach" (MRP-based approach), successfully predicts the behaviour of such materials by taking into account some geometrical parameters such as the particle size distribution or the distance between the nearest-neighbour particles. This model has been validated by a comparison with the experimental data in the literature. We then showed that the MRP-based approach also allowed describing the evolution of complex modules of a thixotropic material undergoing a liquid-solid transition due to the growth and the percolation of an attractive particle network. In the last part of this work, we studied experimentally the influence of the flow history on the structure of a thixotropic colloidal suspension

On étudie la propagation d’ondes acoustiques dans un milieu poreux obéissant à la théorie de Biotet contenant une distribution aléatoire de cavités cylindriques et celle d’une onde acoustique dans un fluide contenant une distribution polydisperse aléatoire de sphères poreuses. Dans le premier cas on utilise la généralisation de Conoir-Norris de la formule de Linton-Martin. En effet, elle permet de prendre en compte le phénomène de la conversion entre les trois ondes (deux longitudinales et une transversale) se propageant naturellement dans un milieu poreux de Biot contenant une distribution aléatoire de cavités. Des expressions analytiques sont trouvées pour les nombres d’onde effectifs des ondes cohérentes dans la limite de Rayleigh (régime basse fréquence). Les approximations des masses volumiques et modules des milieux hétérogènes sont fournies jusqu’à l’ordre de c2 en concentration. Le cas limite des cavités fluides aléatoires dans une matrice élastique est également discuté. Dans le deuxième cas on détermine les nombres d’ondes, modules et masses volumiques effectifs pour des distributions polydisperses de sphères poroélastiques. Pour y parvenir, les formules récentes du nombre d’onde effectif données par Linton et Martin dans le cas dilué monodisperse ont été modifiées. Compte tenu de l’incertitude entourant la prédiction de la distribution en taille des obstacles, trois densités de probabilité différentes sont étudiées et comparées : uniforme, Schulz et log-normal. Plus précisément, la limite de Rayleigh (régime de basse fréquence) est prise en compte lorsque les longueurs d’onde peuvent être supposées très grandes par rapport à la taille des obstacles. Dans cette limite, des formules simplifiées des concentrations sont fournies en fonction du paramètre caractérisant la dispersion en taille. / We study the propagation of acoustic waves in a porous medium obeying the Biot theory and containing a random distribution of cylindrical cavities and that of an acoustic wave in a fluid containing a random polydisperse distribution of porous spheres. In the first case we use the generalization by Conoir-Norris of the Linton-Martin formula. It allows to take into account the phenomenon of the conversion between the three waves (two longitudinal and one transverse) naturally propagating in a porous Biot medium containing a random distribution of cavities. Analytical expressions are found for the effective wavenumbers of coherent waves in the Rayleigh limit (low frequency regime). The approximations of the densities and heterogeneous media modules are presented up to the order of c2 in concentration. The limiting case of random fluid cavities in an elastic matrix is also discussed. In the second case the effective wavenumbers, moduli and density are determined for polydisperse distributions of poroelastic spheres. To achieve this, the recent formulas of the effective wave number given by Linton and Martin in the dilute monodisperse case have been modified. Given the uncertainty for predicting the distribution in size of obstacles, three different probability densities are studied and compared: uniform, Schulz and lognormal. More precisely, the Rayleigh limit is taken into account when the wave lengths can be assumed to be very large compared to the size of the obstacles. Within this limit, simplified formulas for concentrations are provided depending on the parameter characterizing the size dispersion.

L’objectif des travaux présentés dans ce mémoire de thèse est de développer une modélisation numérique de la compaction des poudres composées de particules sécables dans le cadre de la méthode de Dynamique des Contacts en vue d’application au procédé de fabrication du combustible nucléaire. Les particules sont modélisées comme des agrégats cohésifs de fragments potentiels (cellules) de formes polyédriques irréguliers. A l’aide de ce modèle de cellules liées (Bonded Cell Method), nous avons réalisé une étude paramétrique de la résistance des particules par rapport aux paramètres géométriques et mécaniques du modèle. Nos résultats révèlent deux régimes et une mise à l’échelle en loi de puissance de la résistance à la compression en fonction de l’adhésion normale et du rapport entre l’adhérence tangentielle et l’adhésion normale entre cellules. Nous avons optimisé les paramètres du modèle pour la compaction uni-axiale des assemblages d’un grand nombre de particules sécables. Les simulations ont permis d’identifier les mécanismes de compaction et de rupture des particules, et de caractériser l’évolution de la texture et des tailles et formes des fragments. Les résultats obtenus montrent clairement que le processus de compaction est fortement non-linéaire en raison notamment de l’évolution de l’étalement granulométrique qui contrôle la texture et la transmission des contraintes. Enfin, nous avons mené une étude systématique de l’effet de la polydispersité de taille dans le cas de particules sphériques. / The goal of this PhD work is to develop a numerical modeling approach of the compaction of powders composed of crushable particles in the framework of the Contact Dynamics method in view of application to the manufacture process of nuclear fuel. The particles are modeled as cohesive aggregates of potential fragments (cells) of irregular polyhedral shape. Using this Bonded Cell Method, we performed a parametric investigation of the strength of particles with respect to the geometrical and mechanical model parameters. Our results reveal two regimes and a power-law scaling of the compressive strength as a function of the ratio between tangential adherence and normal adhesion between cells. We optimized the model parameters for the uniaxial compression of packings of a large number of crushable particles. The simulations allow us to identify the mechanisms of compaction and fracture of particles, and to characterize the evolution of texture and the sizes and shapes of fragments. Our simulation results clearly show that the compaction process is strongly nonlinear as a consequence of the evolution of particle size distribution, which controls the texture and stress transmission. We also perform a systematic analysis of the effect of size polydispersity in the case of spherical particles.

Orientador: Liliane Maria Ferrareso Lona / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-19T13:42:42Z (GMT). No. of bitstreams: 1 ChaparroMontezuma_GermanGiovanny_M.pdf: 3877380 bytes, checksum: 8f8924d77c55a7ec361451caa074630e (MD5) Previous issue date: 2011 / Resumo: A Polimerização radicalar mediada por nitróxido (NMRP) é uma técnica da polimerização controlada com a habilidade de produzir polímeros com um alto controle da sua microestrutura, estreita distribuição de massa molar e baixos valores de polidispersidade (muito próximos a um). As características do polímero obtidas na polimerização controlada têm aumentado o interesse de levar essa técnica para um nível industrial, no entanto a polimerização controlada ainda apresenta desafios como, por exemplo, desenvolver com sucesso a NMRP em emulsão, a baixas temperaturas e usando nitróxidos de baixo custo e disponíveis comercialmente, como 2,2,6,6-tetrametil-1-piperidiniloxi (TEMPO). A NMRP em emulsão de estireno a temperaturas inferiores a 100 ° C foi realizada com sucesso neste trabalho. TEMPO foi utilizado como agente controlador ainda que este nitróxido normalmente opere a temperaturas acima de 120 °C, sendo demonstrado o controle da massa molar e da polidispersidade, juntamente com uma rápida taxa de polimerização em um sistema de emulsão / Abstract: Nitroxide-mediated radical polymerization (NMRP) is a controlled polymerization technique with the ability to produce polymers with a highly controlled microstructure, narrow molecular weight distribution and low polydispersity values (very close to one). The polymer characteristics obtained in controlled radical polymerization have increased the interest of bringing this technique to an industrial level, however there are still some challenges to be faced, like, successfully develop NMRP in emulsion at low temperatures (lower than 100 °C) with inexpensive nitroxides commercially available, as 2,2,6,6- tetramethyl-1-piperidinyloxy (TEMPO). In this work NMRP of styrene in emulsion at temperatures below to 100 °C was carried out successfully. TEMPO was used as controller agent although this nitroxide usually works at temperatures above 120 °C. It was demonstrated an optimal control of molecular weights and polydispersities, together with a fast polymerization rate in an emulsion system / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Orientadores: Antonio Jose de Almeida Meirelles, Pedro de Alcantara Pessoa Filho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-14T08:10:52Z (GMT). No. of bitstreams: 1 MonteiroFilho_EliasdeSouza.pdf: 12530059 bytes, checksum: 1e25eb71e0f6b6a45db80658070acd61 (MD5) Previous issue date: 2009 / Resumo: A proposta do presente trabalho foi estudar o equilíbrio de fases de sistemas binários e ternários formados por um polímero sintético de óxido de propileno (PO) ou de um co-polímero bloco de óxido de etileno (EO) e PO e/ou um carboidrato de glicose dissolvidos em água. No total 25 diagramas de equilíbrio líquido-líquido (ELL) foram determinados a temperaturas entre 288,15 e 308,15 K para sistemas ternários, 4 diagramas de ELL para sistemas binários e 9 conjuntos de dados de atividade de água para soluções aquosas binárias e ternárias de diversos dos reagentes estudados. Dos diagramas de ELL ternários, 18 são diagramas cujo oligossacarídeo é polidisperso. A polidispersão influencia significativamente no comportamento do sistema. A temperatura também foi adotada como variável em alguns casos. Os resultados obtidos contribuem para elucidar o comportamento em solução aquosa de co-polímeros bloco de EO e PO com diversas massas molares e relações entre os blocos, e de glicose, maltose ou diversos polímeros de glicose em uma faixa razoável de temperaturas. Estes polímeros são bastante pesquisados para uso em sistemas bi ou mesmo polifásicos para purificação de substâncias de origem biotecnológica. Diferentes tipos de diagramas foram observados, bem como comportamentos diversos da atividade de água. A modelagem termodinâmica foi realizada com base em diversas equações propostas e de uso corrente. Incorpora, ainda, o comportamento diferenciado devido à polidispersão e à temperatura. Os resultados indicam que um bom modelo termodinâmico é capaz não apenas de fornecer informações para controle de processos, mas também sobre as interações moleculares e, com isso, predizer o comportamento de sistemas mais complexos / Abstract: This work relates phase equilibrium of binary and ternary systems formed by aqueous mixtures of EO-PO block co-polymers of five different molar masses and EO/PO ratios, and maltodextrins of three different mean molar masses studied at 298.15 K. 25 Liquid-Liquid Equilibrium (LLE) phase diagrams for ternary systems at temperatures ranging from 288,15 to 308,15 K, plus 4 LLE diagrams for binary systems and 9 water activity data sets, were determined. Of the ternary systems, 18 contain a polydisperse carbohydrate, and this polidispersity influences markedly the system's behavior. Temperature was also investigated in some cases. The results obtained contribute to elucidate the behavior of water solutions containing EO-PO block co-polymers of various molar masses and blocks ratios and glucose, maltose or several glucose polymers in a reasonable temperature range. These polymers are investigated for applications in aqueous two-phase systems. Different kinds of diagrams were observed, as well as water activity reductions. Thermodynamic modeling was performed employing current models. Also, polydispersity and temperature effects were incorporated. The results indicate that a good thermodynamic model is capable of not only provide information for process control purposes, but also about molecular interaction and predict the behavior of more complex systems / Universidade Estadual de Campi / Engenharia de Alimentos / Doutor em Engenharia de Alimentos