O sucesso da conclusão de um poço por perfuração e o custo do projeto estão relacionados às propriedades dos fluidos de perfuração. O estudo experimental foi realizado a partir da determinação e análise das curvas de tensão de cisalhamento versus taxa de deformação de suspensões aquosas de bentonita e carboximetilcelulose com diferentes concentrações de NaCl. Investigou-se, inicialmente, o comportamento reológico de suspensões de carboximetilcelulose 0,5% (em massa) com concentrações de sal, NaCl de 0 a 4% (em massa), para temperaturas variando de 14 a 26ºC. Os resultados experimentais possibilitam a caracterização reológica destas soluções como fluidos pseudoplásticos e indicam que a adição de NaCl em soluções com CMC alteram significativamente o comportamento reológico desse tipo de solução. Numa segunda etapa, estudou-se o comportamento reológico de suspensões de bentonita e carboximetilcelulose em diferentes concentrações de sal, NaCl. Empregaram-se soluções contendo 4,8 % de bentonita, 0,5 % de carboximetilcelulose e concentrações de 0 a 4% de NaCl. Constata-se o comportamento tixotrópico destas suspensões e a forte dependência com a concentração de sal. O estudo foi complementado com uma análise comparativa dos resultados do comportamento reológico obtidos por reômetro de cilindros coaxiais modelo Brookfield e o viscosímetro FANN 35 A, usualmente empregado na análise de fluidos de perfuração. O equacionamento do escoamento do fluido nos aparelhos permitiu uma interpretação mais detalhada dos valores descritos na norma, obtendo-se uma equivalência dos valores medidos em campo com os obtidos no reômetro Brookfield apesar de as faixas de operação de taxas de deformação serem distintas. / The properties of drilling fluids have a very significant effect on the successful of a well completion and the project costs. The experimental study was conducted based on the determination and analysis of the curves of shear stress and shear rate of aqueous suspensions composed of bentonite and carboxymetil cellulose at different concentrations of NaCl. The rheological behaviour of carboxymetil cellulose suspensions 0.5% w/w at NaCl concentrations in the range of 0 to 4% w/w from 14 to 26°C was studied. The experimental results allow the rheological characterization of these solutions as pseudoplastic fluid. It was observed that the addition of NaCl to CMC solutions changes its rheological behaviour significantly. In addition, the rheological behaviour of 4,8% bentonite suspensions with 0,5% carboxymethyl cellulose at different concentrations of NaCl in the range of 0 to 4% was studied. The characterization of these solutions showed thixotropic behaviour and a strong dependence on the salt concentration. The study was complemented with a comparative analysis of the results obtained by using a coaxial cylinders rheometer model Brookfield and the FANN Model 35 A viscometer, usually employed in drilling fluids analysis. The analytical solutions allowed a more detailed interpretation of the values described in the standard resulting in an equivalence between the measured values obtained in the field and in the Brookfield rheometer despite the differents shear rate ranges.

Neste trabalho, várias técnicas foram utilizadas para estudar mesofases constituídas por laurato de potássio, cloreto de decilamônio, água e sulfato de brucina. Este sistema foi eleito por apresentar a fase colestérica biaxial, cuja caracterização continua se constituindo um problema digno de investigação. Foram efetuadas medidas reológicas sobre sistemas nemáticos e colestéricos, em diferentes composições e condições. Os valores das viscosidades aparentes foram calculados e o comportamento caracterizado. Para os estudos de RMN, introduziu-se nas amostras uma molécula probe, o racêmico dl alanina, procurando-se verificar se havia diferença na interação dos enantiômeros d e I com a matriz colestérica. Os espectros foram obtidos com variação de temperatura. Compararam-se os dados de variação do parâmetro de ordem, obtidos dos acoplamentos diretos, com a semi largura da linha larga dos espectros de próton, para obter informações sobre o comportamento da alanina e das micelas colestéricas. Todas as fases foram acompanhadas por estudos de microscopia sob luz polarizada, técnica simples e eficiente utilizada para caracterizar tipos de fases de cristais líquidos. / In this work, several techniques were used to study mesophases constituted by potassium laurate, decylammonium chloride, water and brucine sulfate. This system was chosen for presenting a cholesteric biaxial phase, whose characterization continues to be worthy of investigation. Rheological measurements were made on nematic and cholesteric systems, in different compositions and situations. The values of apparent viscosity were calculated and the behaviour was characterized. For the RMN studies, a probe moIecule, the racemic form of dl alanine, was introduced in the sampIes trying to verify difference between in interaction of the enantiomers d and I with the main cholesteric matrix. The spectra were obtained with temperature variation. It was compared the data of variation of the order parameter, obtained from the direct couplings, with the half width of the wide line of the proton spectra, to obtain information about the behaviour of the alanine and of the cholesteric micelles. All the phases were accompanied by microscopy studies under polarized light, simple and efficient technique to characterize types of liquid crystal phases.

Le combustible nucléaire pressenti pour les réacteurs de quatrième génération à neutrons rapides refroidis au sodium présente différentes caractéristiques qui le différencient du combustible utilisé dans les Réacteurs à Eau Pressurisée, notamment : une structure homogène (U,Pu)O2, une géométrie annulaire et une forte teneur en PuO2. Le procédé de fabrication des pastilles de combustible comprend la réalisation d’un mélange UO2/PuO2 par cobroyage suivie d’une mise en forme par pressage. Cependant, le mélange UO2/PuO2 cobroyé n’a pas les propriétés adaptées à un remplissage reproductible des moules de presses annulaires. Il s’agit donc d’identifier une opération intermédiaire, entre le cobroyage et la mise en forme, pour faciliter le remplissage des moules. Pour orienter le choix de cette opération, une étude à effets séparés a été réalisée sur des granulés d’UO2, considérés représentatifs de la poudre broyée en première approche. Les caractéristiques physiques cibles qui ont été étudiées sont la granulométrie et la morphologie (état de surface) de la poudre. Ainsi, des mélanges de granulés de tailles différentes ont été caractérisés pour évaluer l'influence de la quantité de fines (particules inférieures à 100 μm) sur les propriétés rhéologiques. En parallèle une intercomparaison entre les cellules de cisaillement de volumes et de types différents (Cellule de Schulze et FT4) a été effectuée afin d’avoir un bon compromis entre la quantité de poudre utilisée et la qualité des résultats. Un premier objectif a été de déterminer quelle proportion de fines est acceptable. Par ailleurs, pour évaluer l’effet de l’état de surface des granulés, une opération de type sphéroïdisation a été réalisée. Elle conduit à modifier la rugosité des granulés. Il a été montré que le taux de fines et la rugosité de surface sont deux paramètres influents qui permettent de modifier les propriétés rhéologiques. Notamment dans le cadre de ces travaux, la présence de fines de moins de 100 μm ne semble pas avoir d’impact négatif sur la mise en écoulement jusqu’à une proportion proche de 10%m. Par contre d’autres propriétés telle que la perméabilité sont sensibles à la proportion de fines même en dessous de 10%m. Une opération de sphéroïdisation permet d’améliorer les propriétés de mise en écoulement de la poudre même au-delà de 10%m de fines. Ces résultats font apparaitre deux modes d’action possibles qui sont la sélection granulométrique et la sphéroïdisation, cette dernière semblant la plus adaptée pour notre application. / The nuclear fuel for the fourth generation sodium-cooled fast neutron reactors presents characteristics which differentiate it from that used in Pressurized Water Reactors: a homogeneous structure (U,Pu)O2, an annular geometry and a high content of PuO2. The manufacturing process of the fuel pellets starts with the realization of a UO2/PuO2 mixture by co-grinding followed by forming by pressing. However, the UO2/PuO2 mixture does not exhibit the suitable properties for a reproducible filling of annular press moulds. An intermediate operation, between the co-grinding and the shaping, is necessary to facilitate the filling of the moulds. To direct the choice of this operation, a separate effects study was carried out on UO2 granules, considered as representative of the crushed powder in a first approach. The investigated target physical characteristics are the powder size distribution and morphology. Therefore, mixtures of granules of various sizes were characterized to evaluate the influence of the quantity of fines (particles with a size lower than 100 μm) on the rheological properties. In parallel an intercomparison study between shear cells of different volumes and types (Schulze cell and FT4) was carried out in order to have a good compromise between the quantity of powder used and the quality of the results. A first objective was to determine the proportion of fines acceptable. Then to evaluate the effect of the surface quality of the granules, an operation of spheroidization was carried out. This resulted in modifying the granules roughness. It has been shown that both the fines ratio and the surface roughness are influential parameters that make it possible to modify the rheological properties. In particular within the framework of this study, the presence of fines with a size lower than 100 μm does not seem to have a negative impact on incipient flow up to about 10 w%. On the contrary, other properties such as permeability are sensitive to the fines amount, even below 10 w%. A spheroidization stage enables to improve incipient flow properties of the powder even above 10 w% of fines. These results lead to two possible action modes, which are the grain size selection and the spheroidization, the latter being the most adapted for our application.

We formulate a model for acoustic excitations in a magnetorheological fluid. Constitutive equations are derived for Navier-Stokes flow coupled with Maxwell's Equations. The viscosity of the fluid is modified to reflect the dependence of waves propagating within the fluid itself and in the case where they propagate along the network of particles.

Les écoulements pyroclastiques sont des écoulements volcaniques complexes dont le comportement physique fait encore l'objet de débats. Ils sont composés de deux parties : l'écoulement dense basal, riche en particules et en blocs, surmonté par la déferlante, diluée et turbulente. Les interactions entre ces deux parties ne sont pas bien comprises, tout comme leurs échanges de masses et de quantités de mouvement. Partant de ce constat, cette thèse se concentre sur l’étude des mécanismes de formation de la déferlante à partir de l’écoulement dense.Les expériences mettent en évidence un mécanisme de formation d'un écoulement dilué par l’alternance d’incorporation d'air et d’élutriation des particules fines d’un lit granulaire dense soumis à des vibrations. L'air est aspiré dans le lit granulaire pendant les phases de dilatation puis expulsé pendant les phases de contraction. Une partie des particules est alors soutenue par l'air turbulent expulsé et forme un mélange de gaz et de particules qui, plus dense que l’air, se transforme en un écoulement de gravité. Extrapolé à l’échelle d’un volcan, ce mécanisme d’incorporation d’air et d’élutriation peut être reproduit par une topographie rugueuse, où chaque obstacle génère une compaction puis une dilation de l’écoulement dense. La quantification du mécanisme a été effectuée et l’approche expérimentale a permis d’aboutir à une loi reliant le flux de masse de la partie dense vers la déferlante à la vitesse de l’écoulement dense. Le modèle numérique est utilisé dans un premier temps pour étudier la rhéologie de l’écoulement dense qui, en contrôlant sa vitesse, contrôle le flux de masse précédemment évoqué. Un chapitre est consacré à l’effet de la fluidisation de l’écoulement dense sur sa rhéologie. Les résultats montrent que la fluidisation par les gaz est capable d’expliquer à la fois la grande mobilité de ces écoulements, ainsi que la formation des morphologies terminales en lobes et chenaux. L’ingestion d’air dans un écoulement au cours de sa mise en place semble pouvoir expliquer une partie de la dynamique des écoulements denses. Des rhéologies simples, de premier ordre, ont également été analysées : la rhéologie de Coulomb, la rhéologie plastique, et la rhéologie à coefficient de frottement variable. Les résultats montrent que la rhéologie plastique semble la mieux adaptée pour reproduire la vitesse et l’extension des écoulements denses.Ce modèle numérique a ensuite été utilisé pour tester la loi de flux de masse obtenue suite aux expériences de laboratoire. Appliqués à l’effondrement de dôme du 25 juin 1997 à la Soufriere Hills de Montserrat, les résultats montrent que les simulations reproduisent des dépôts de déferlantes dont l’épaisseur et l’extension sont tout à fait réalistes. Les simulations reproduisent même les écoulements denses secondaires issus de la sédimentation de la déferlante puis de la remobilisation des dépôts. Les cycles d’ingestion/expulsion d’air dans l’écoulement dense, par interaction avec la topographie, expliqueraient donc à la fois la grande fluidité des écoulements denses et la formation des déferlantes pyroclastiques. Les résultats de cette thèse mettent à jour un mécanisme nouveau qui pourrait être la clé de la mise en place des écoulements pyroclastiques et pourrait permettre d’améliorer la prévision future des risques et des menaces par modélisation numérique. / Small volume pyroclastic density currents are complex volcanic flows, whose physical behaviour is still debated. They comprise two parts: the pyroclastic flow, rich in particles and blocks, overridden by the ash-cloud surge, a turbulent and dilute flow. The interactions between these two parts are not fully understood, as well as their exchanges of mass and momentum. Therefore, the thesis focuses on the investigation of ash-cloud surge formation mechanisms from the pyroclastic flow. The experiments reveal a mechanism of dilute flow formation by alternation of air incorporation into and elutriation of fine particles from a dense granular bed subjected to vibrations. The air is aspirated into the granular bed during dilatations, and expulsed during the contraction phases. A part of the particles are then sustained by the turbulent expulsed air and form a mixture of gas and particles that transforms into a gravity current. Extrapolated to a volcanic edifice, this mechanism of air incorporation and elutriation can be reproduced by a rough topography, where each obstacle generates a compaction followed by a dilatation of the pyroclastic flow. The quantification of the mechanism has been accomplished and the mass flux from the dense flow to the ash-cloud surge has been deduced.The numerical model is first used to study the pyroclastic flow rheology, which controls the velocity of the flow, and then the mass flux previously mentioned. One chapter is dedicated to the fluidization effect on the pyroclastic flow rheology. Results show that this mechanism can explain the long runout of these flows, and also the formation of levées and channel morphologies. The air ingestion in the flow during its movement could explain a part of the pyroclastic flows dynamic. Simple rheologies has also been analyzed: a Coulomb rheology, a plastic rheology, and a variable friction coefficient rheology. Results show that the plastic rheology seems to be the most adapted rheology to simulate the pyroclastic flow dynamic. Then, the numerical model has been used to test the mass flow law obtained through experiments. Applied to the 25 June 1997 dome collapse at Soufrière Hills Volcano at Montserrat, results show that the simulations reproduce accurately the extension and the thickness of the surge deposits. The simulations are also able to reproduce the surge derived pyroclastic flow, generated by remobilisation of surge deposits. The cycles of ingestion/expulsion of air in the pyroclastic flow by interactions with the topography could explain both the great fluidity of these flows and the formation of ash-cloud surge. These results highlight a new mechanism that could be a key process in pyroclastic flow dynamic, which could improve significantly the hazard and risk assessment using numerical model.

The process of a single cell evolving into a complex organism results from a series of coordinated movements of cells and tissues, especially during early embryo development. Although a wealth of morphological data characterises the shapes and movements of cells in embryos, how these movements are driven, patterned and controlled, and how this patterning is related to the mechanical properties of tissues remains unknown. Four-pole electromagnetic tweezers have been developed to probe the mechanical properties of living embryonic tissues that are undergoing active morphogenetic development. The device is capable of generating magnetic forces in the order of nano-Newtons on a grafted magnetic bead. The local passive mechanical properties of the tissues can be characterised by measuring the three-dimensional bead movement and analysing cell shape changes and cell rearrangement in response to this externally applied force. The magnetic device is used to probe the rheology in early zebrafish embryos between high stage (3.3 hpf) and the onset of gastrulation (5.3 hpf) when rapid cell cycles give way to a hollow sphere of cells. The tissue response to the applied force is modelled as linear visco- elastic. The embryo becomes stiffer and more viscous during this period of development, showing that a loose collection of cells becomes cohesive tissues. A computational model is used to explore how cells respond to local or global mechanical perturbations in two systems. First, the model simulates the movement of the bead within an embryo, and the results illustrate the generation, patterning and relaxation of the local cell stress around the bead. Second, the model reproduces the autonomous changes in mitotic cells within a stretched monolayer, and the results show that propensity of cells to divide along their long axis facilitates stress relaxation and contributes to tissue homoeostasis.

No presente trabalho, avaliou-se os efeitos individuais e combinados de nove enzimas comerciais sobre as propriedades reológicas de massa das farinhas de trigo, com o objetivo de identificar seus efeitos sinérgicos ou antagônicos e as suas concentrações ótimas, como alternativa para substituição de oxidantes químicos no tratamento de farinhas. α-Amilases de origem fúngica (AMY-F), bacteriana (AMY-B) e maltogênica (AMY-M), xilanases fúngica (XYL-F) e bacteriana (XYL-B), glucose oxidase (GOX), lacase (LAC), lipase (LIP) e transglutaminase (TG) foram testadas em dois tipos de farinha: uma farinha forte padrão (farinha A) e uma farinha fraca comum (farinha B). Inicialmente, as enzimas foram adicionadas individualmente na farinha onde, seus efeitos sobre Falling Number (FN), farinografia e alveografia, foram avaliados variando-se suas concentrações de 25 - 833 U.kg-1, a fim de se identificar as faixas de concentração ideais de cada uma delas. Identificou-se que as α-amilases afetaram principalmente as propriedades farinográficas, reduzindo a capacidade de absorção de água (WA) e tempo de estabilidade (ST) das massas. Para o ajuste de FN, AMY-B (150 U.kg-1) foi mais eficiente que AMY-F (583 U.kg-1) e AMY-M (583 U.kg-1). As xilanases melhoraram o valor de W (10-4 J) e razão P/L, sendo que em todos os testes XYL-B foi mais eficiente do que XYL-F. Na concentração de 25 U.kg-1, GOX e LAC melhoraram o ST, razão P/L e valor de W; no entanto, aumentaram o tempo de desenvolvimento (DT) das massas. LIP (150 U.kg-1) promoveu a melhora no W e DT, enquanto que TG não apresentou efeitos significativos na maioria dos parâmetros avaliados. A partir disso, os efeitos combinados das enzimas foram avaliados através de dois planejamentos experimentais sequenciais. Para farinha A, a combinação enzimática ótima foi AMY-B (166 U.kg-1), AMY-M (133 U.kg-1), XYL-B (150 U.kg-1), GOX (8 U. kg-1) e LIP (150 U.kg-1). Identificou-se um efeito sinérgico entre XYL-B e GOX na melhoria do W e razão P/L. Para a farinha B, a combinação enzimática ótima foi AMY-B (150 U.kg-1), LIP (150 U.kg-1), GOX (100 U.kg-1) e LAC (200 U.kg-1), sendo que GOX e LAC apresentaram um efeito cooperativo, quando usadas em concentrações opostas. As combinações enzimáticas foram mais eficientes do que a azodicarbonamida, cujo efeito, mesmo na concentração máxima (40 ppm) permitida pela legislação, não melhorou os parâmetros reológicos das massas. Foi demonstrado que é possível a substituição de oxidantes químicos por enzimas para o tratamento de farinhas, a fim de melhorar a reologia das massas, mesmo para uma farinha fraca, tornando-a adequada para panificação. / In the present work, it was evaluated the individual and combined effects of nine commercial enzymes on the rheological properties of dough wheat flour, aiming to identify synergistic and antagonist effects between the enzymes and their optimal concentrations as substitutes of chemical oxidants. Fungal (AMY-F), bacterial (AMY-B) and maltogenic (AMY-M) -amylases, fungal (XYL-F) and bacterial (XYL-B) xylanases, glucose oxidase (GOX), laccase (LAC), lipase (LIP) and transglutaminase (TG) were tested in two types of flour: standard strong flour (flour A) and common weak flour (flour B). Initially, Falling Number, farinography and alveography analysis were carried out varying the enzymes concentrations from 25 to 833 U.kg-1, to identify the ideal ranges of each of them to improve the rheological characteristics of dough wheat flour. It was identified that α-amylases affected mainly the farinographic properties, reducing the water absorption (WA) and stability time (ST). AMY-B was the most effective enzyme for setting the FN, requiring 150 U.kg-1, while for AMY-F and AMY-M it was necessary 583 U.kg-1. In all tests, XYL-B was more efficient than XYL-F, but both improved the W (10-4 J) value and P/L ratio. At 25 U.kg-1, GOX and LAC had important improves on the ST, P/L ratio and W value, however increased undesirably the development time (DT). LIP (150 U.kg 1) promoted the improvement in W value and DT, while TG had not significant effects on most of the evaluated parameters. After that, the combined effects of enzymes were evaluated through two sequential experimental designs. For flour A, the optimal combination of enzymes was AMY-B (166 U.kg-1), AMY-M (133 U.kg-1), XYL-B (150 U.kg-1), GOX (8 U.kg-1) and LIP (150 U.kg-1). It was identified a synergistic effect between XYL-B and GOX to improvement of W value (10-4 J) and the P/L ratio. For the flour B, the optimal combination of enzymes was AMY-B (150 U.kg-1), LIP (150 U.kg-1), GOX (100 U.kg-1) and LAC (200 U.kg-1). GOX and LAC presented a cooperative effect, when they were used at opposite concentrations. The enzymes mixtures were compared with chemical oxidant azodicarbonamide, and, even at the maximum concentration (40 ppm) allowed by Brazilian Health Surveillance Agency, the enzyme mixture was more effective. It was demonstrated that it is possible to perform the complete substitution of chemical oxidants by enzymes in order to adequate and improve the rheological parameters of dough wheat flours, even for a weak flour, making it suitable for bakery.

Les suspensions minérales de particules fines sont connues pour leur comportement non-Newtonien pendant l'écoulement. Les interactions particule-particule dans de tels systèmes (c’est-à-dire, suspensions minérales) ne sont pas limitées au contact physique, e.g. collision et frottement. La capacité des minéraux de développer une charge dans l'environnement aqueux justifie des comportements différents des systèmes similaires de première vue. C’est à dire qu’étant caractérisées avec la même fraction volumétrique, composition chimique et granulométrie des solides et densité de dispersant, deux suspensions peuvent montrer un comportement rhéologique différent en raison de la chimie de la solution. Dans ce cas, la composition ionique du dispersant définira la charge des particules, et donc le degré d'agglomération/dispersion dans la suspension. Les argiles phyllosilicates sont connues pour être particulièrement problématiques dans les processus de valorisation des minéraux. L’origine de ces minéraux phyllosilicates implique leur inhomogénéité chimique spatiale, ce qui signifie que le bord et la face de la particule montrent des propriétés chimiques et physiques différentes. La présence de tels minéraux dans les dispositifs d'agitation (réservoirs d'agitation, cellules de flottation) est souvent caractérisée par la coexistence de volumes de suspension stagnants et agités, ce qui a un impact négatif sur l'efficacité de l'agitation. Dans ce travail, les suspensions aqueuses diluées de Na-bentonite ont été examinées par vélocimétrie par imagerie par résonance magnétique afin d'étudier l'influence du pH et du type d'électrolyte monovalent sur leur comportement rhéologique local. Les résultats ont montré que les suspensions contenant 0,1% de solide en volume peuvent présenter une bande de cisaillement, une localisation de cisaillement ou aucun phénomène local en fonction de la chimie du milieu de suspension. Il a été suggéré que l’existence d’une «master curve» (ou courbe d’écoulement globale) pour les suspensions diluées dépendait de l’organisation des particules de bentonite dans la suspension, cette organisation est influencée par la chimie de solution et l’historique des contraintes précédentes. Dans l'étape suivante, une seconde et troisieme phases minérales (hématite et quartz) ont été ajoutées dans la matrice de bentonite. L’intérêt dans tels systèmes est lié au comportement sous écoulement des matrices formées avec des types de contacts différents entre particules. Les types de contacts établis dans les suspensions avec une chimie différente du milieu ont été discutés, ainsi que leurs propriétés d’écoulement / Fine particle mineral slurries are known to exhibit non-Newtonian behavior under the load. The particle-particle interactions in such suspensions go beyond physical contact due to the collision and friction. An ability of minerals to gain the charge in the aqueous environment justifies different behaviors of the similar systems. Being characterized with the same volumetric fraction, chemistry and particle size distribution of solids, and specific gravity of dispersing media, two suspensions can possess different rheological behavior due to the chemistry of the solution. In this case, the ionic composition of the media defines particle charging, and thus the degree of agglomeration/dispersion in the suspension. Phyllosilicate clays are known to be particularly problematic in the mineral beneficiation processes. Their nature leads spatial chemical inhomogeneity, meaning that the particle edge and face possess different chemical and physical properties. The presence of such minerals in the stirring devices (stirring tanks, flotation cells) is often characterized with coexistence of stagnant and agitated volumes of slurry, which negatively impacts the efficiency of stirring. In this work, the dilute aqueous Na-bentonite suspensions were examined via magnetic resonance imaging velocimetry to investigate the influence of pH and type of monovalent electrolyte on their local rheological behavior. The results indicated that suspensions with 0.1 vol.% solid can exhibit shear banding, shear localization or no local phenomenon as a function of chemistry of the suspending media. It was suggested that the existence of master curve (or global flow curve) for dilute suspensions was dependent on the bentonite particle organization in the suspension, which was influenced by the chemistry of the environment and the previous flow history. In the next step, second mineral phase (hematite or quartz) was added to the bentonite matrix. The interest in examination of such systems is related to the flow behavior of matrix formed with different kinds of inter-particle contacts. For example, at pH 4 the resulting electrostatic interaction between positively charged bentonite edge and negatively charged quartz is attractive, whereas at the same pH it is repulsive with the positively charged hematite. These electrostatic interactions result in different organization of matrix particles around another mineral phase. In the system with solely repulsive interactions between all sites of all mineral phases (e.g., quartz and bentonite, pH 10) the deviation from Newtonian behavior is justified by the shear-induced particle rearrangements, collision and friction. The difference in the arrangement of bentonite particle aggregates around the hematite or quartz particles was observed using SEM. As a next step the third mineral phase was added. The types of contacts established in the suspensions with different chemistry of the media were discussed along with their flow propperties

The rheological behavior analysis of Engineered Cementitious Composites (ECC) is key to understand how the different preparation techniques affect the composite mechanical performance. However, the rheological assessment of reinforced materials becomes more complex since fibers usually cause flow disturbances not found in nonreinforced cementitious materials. Besides that, simple workability measurement techniques are not able to fully understand the composite behavior in the fresh state creating the need for more precise techniques to be employed. The main objectives of this study were to evaluate the ECC rheological behavior using different rheometer devices (Vane system and Ball measuring system) and investigate the influence of mixing processes on the fiber homogenization and rheological behavior. Additionally to this, a link between rheological behavior and mechanical performance was investigated. In the end, the ball measuring system revealed to be more efficient than the vane system when evaluating the composite rheological behavior. In addition, the mixing process influenced the rheological behavior of PVA-ECC especially regarding the moment which fibers are added. Fiber addition after mortar mixture improved fibers homogenization and reduced mixing energy by around 8%. Moreover, a correlation between rheological and mechanical properties showed that a 2-times variation in either yield stress or viscosity can lead to a variation of more than 50% in flexural strength without significantly affecting the composite compressive strength. It was also found that the lower the composite yield stress and viscosity the higher was its ultimate strain. To conclude, all those parameters contributed to understand the composite rheological behavior and globally optimize its performance. / Sem resumo

Este trabalho tem como objetivo caracterizar experimentalmente a difusão anômala de microesferas em células com alta resolução temporal. As microesferas são cobertas com um peptídeo para que elas fiquem aderidas ao citoesqueleto celular (CSK), de forma que quando o CSK se movimenta, as microesferas se movimentam junto. A grande parte dos trabalhos na literatura usa técnicas ativas, que consistem em aplicar uma perturbação na célula, para estudar a movimentação das microesferas, diferente da técnica usada neste trabalho, que é passiva. A vantagem de usar a técnica passiva é que é possível olhar a difusão das microesferas, sem haver fatores externos ativos atuando, porque o CSK já é um ambiente sujeito a forças dos próprios motores celulares, o que está relacionado com o comportamento anômalo. Ao calcular o deslocamento quadrático médio (MSD) das microesferas, os regimes aos quais as microesferas estão sujeitas, são o subdifusivo e o superdifusivo, e ambos possuem características que podem ser consideradas comportamento anômalo. Neste trabalho focamos em estudar a difusão anômala a altas frequências, usando uma câmera que pode chegar a 1000 frames por segundo (fps) para observações curtas, ou em torno de 200 fps, sustentável por longos tempos, a fim de evidenciar o comportamento anômalo. Conseguimos mostrar que a movimentação das microesferas segue uma lei de potência para deslocamentos normalizados |Z| > 3, o que indica que o fenômeno é livre de escala, corroborando com a hipótese de o citoplasma celular ter um comportamento do tipo mole. Além disso, como a análise do movimento é baseada na análise de imagem da posição das microesferas, propusemos um estudo para estimar o erro na posição das microesferas. / The aim of this master\'s thesis is to characterize experimentally anomalous diffusion of microbeads in cells with high temporal resolution. The microbeads are coated with a peptide, such that they can bound to integrins, which is a specific cell surface receptor, thus when the cytoskeleton moves the microbeads move together. The majority of works in scientific literature deals with active techniques, that consists of applying a disturbance on the cell, in order to investigate the movement of the beads, differently from the passive technique used in this work. The advantage of using the passive technique is that it makes possible to look to diffusion without having external active factors, because the cell cytoskeleton itself is an environment subjected to forces, provided by cell motors, which has been related to the anomalous behavior in the mean squared displacement. When calculating the microbeads mean squared displacement (MSD), they are subjected to the subdiffusive and supperdifusive regimes, and both have characteristics that can be considered anomalous behavior. Our goal was to study anomalous diffusion at high frequencies by using a camera that reaches up to 1000 frames per second (fps), for shorter observation times, or around 200 fps, sustainable for longer observation times, having the purpose of evidencing the anomalous behavior. We were able to show that the microbeads movement follows a power law for normalized displacements |Z| > 3, indicating that the phenomenon is scale-free, agreeing with the hypothesis that the cellular cytoplasm has a soft glassy behavior. Besides, since the movement analysis is based on the microbeads position image analysis, we have proposed a way to estimate the error in the microbeads position.