Orientador: Rosiane Lopes Cunha / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-13T14:14:55Z (GMT). No. of bitstreams: 1 Sato_AnaCarlaKawazoe_D.pdf: 2187954 bytes, checksum: 9f67420e2e9bb6fdb40e51d15be43b4e (MD5) Previous issue date: 2009 / Resumo: A influência das características físicas e químicas do meio dispersante sobre a reologia de suspensões-modelo foi avaliada visando o entendimento do comportamento de sistemas reais como as polpas de frutas. Para isto, o trabalho foi dividido em duas etapas: 1) estudo do efeito da composição de sistemas-modelo de soro de polpas de frutas no comportamento reológico, e 2) estudo de suspensões-modelo de diferentes partículas dispersas em matrizes com diferentes propriedades físicas e químicas. Na primeira etapa, foi verificado o efeito da presença de pectinas de alto e baixo grau de metoxilação, assim como de suas misturas. Os resultados mostraram um efeito sinergístico da mistura destes diferentes tipos de pectinas, devido à maior viscosidade e pseudoplasticidade dos sistemas mistos quando comparados aos sistemas com um único tipo de pectina. Assim, ressaltou-se a importância dos diferentes tipos de ligação no comportamento reológico destes sistemas. A segunda etapa permitiu a compreensão das interações entre partículas e partícula-solvente e a sua influência no comportamento reológico de suspensões-modelo. De um modo geral, as interações entre partículas e partícula-solvente foram maiores nos meios menos viscosos e polares. Tais resultados foram refletidos pelo valor ajustado da fração máxima de empacotamento (fm) por diferentes modelos, dado que foi possível a adição de maior quantidade de sólidos para os sistemas com menos interações. Xantana foi adicionada às matrizes dispersantes para promover pseudoplasticidade, indicando comportamentos distintos quando adicionadas em água pura e em soluções aquosas de glicerina. No primeiro caso, as matrizes apresentaram comportamento altamente pseudoplástico, enquanto que a adição de mesma quantidade de xantana nas soluções aquosas de glicerina levou a um grande aumento na viscosidade, com menor influência no valor do índice de comportamento de escoamento. A adição de sólidos nestes dois tipos de matrizes levou a comportamentos distintos. No primeiro caso verificou-se uma leve desestruturação do sistema, refletido principalmente pela maior influência do módulo complexo com a freqüência e menor variação na viscosidade relativa das suspensões. Por outro lado, o aumento na fração de sólidos nos sistemas compostos com xantana, glicerina e água levou a suspensões mais estruturadas. Assim, os resultados apresentados mostram que além das características das partículas, as propriedades químicas e reológicas da matriz dispersante são essenciais na determinação do comportamento estrutural e de escoamento de suspensões e portanto, não deveriam ser desprezadas pelos modelos existentes / Abstract: The influence of the physical and chemical properties of dispersing matrices on the rheological behavior of model-suspensions was evaluated, aiming the understanding of real suspensions such as fruit pulps. The present research was divided into two parts: 1) influence of composition of serum of fruit pulps on their rheological characteristics, through the study of model-systems, and 2) evaluation of model-suspensions of different particles dispersed into matrices with distinct characteristics (physical and chemical). In the first part, the effects of low and high methoxy pectins were evaluated, as well as their mixture. Results indicated a synergistic effect on the mixture of different sorts of pectin, which was observed by the higher viscosity and pseudoplasticity of mixed systems as compared to pure pectin ones. Such results allowed emphasizing the importance of different binding characteristics on the rheological properties of these systems. The second part allowed for the comprehension of interparticle and particle-matrix interactions, and their influence on the rheological behavior of model suspensions. Generally, interactions were more pronounced at low viscous and polar matrices, which reflected the lower maximum packing fraction (fm) fitted by different models. Xanthan was added to dispersing matrices to impart pseudoplasticity, showing distinct behaviors when mixed in pure water and aqueous glycerin solutions. In the first case, matrices showed highly shear thinning behavior, while the addition of the same amount of xanthan in glycerin aqueous solutions promoted a significant increase on viscosity, with lower influence on the flow index behavior (n). Thus, distinct behavior was observed when increasing solids concentration on these two matrices. In the first case, the increase of the dependency of complex modulus with frequency and the lower influence of the relative viscosity reflected a slight loss of structure with solids addition. On the other hand, increasing solids content on systems composed with xanthan, glycerin and water increased structuring. Thus, results indicated that beyond particles characteristics, which have already been widely studied in literature, the knowledge of the chemical and rheological properties of dispersing matrix is of great importance on structural behavior of suspensions / Doutorado / Doutor em Engenharia de Alimentos

Les paramètres de formulation et les conditions de mise en place du béton frais affectent ses propriétés mécaniques et sa durabilité à l’état durci et in extenso la durabilité de l’ouvrage construit. De ce fait, l’ouvrabilité du béton doit être judicieusement choisi selon la géométrie de l’élément à couler et la disposition des armatures. Par exemple, le béton autoplacant (BAP) se met en place sous son propre poids et épouse adéquatement les coffrages sans apport de vibration mécanique. Ainsi le BAP est généralement utilisé pour couler les éléments ayant une géométrie complexe ou difficilement accessible. Le comportement à l’écoulement lors de la mise en place de cette classe de béton peut difficilement être prédit à l’aide des essais empiriques tels que le cône d’Abrams. Par ailleurs, une légère variation des propriétés des constituants peut conduire à un béton avec des faibles performances à l’écoulement. La rhéologie, une branche de la physique qui étudie l’écoulement des fluides, permet une meilleure description des propriétés à l’écoulement des BAP et facilite la compréhension de ce matériau. Le BAP peut être considéré comme une suspension de gros granulats dans un fluide suspendant (mortier). Dans ce cas, des modèles rhéologiques analytiques peuvent être exploités pour prédire les propriétés rhéologiques de ces matériaux et comprendre leur comportement à l’écoulement. Néanmoins, l’applicabilité de ces modèles est fonction de plusieurs paramètres, notamment la nature de la phase suspendante considérée (pâte, mortier de béton équivalent ou mortier), caractéristiques des particules solides, historique de cisaillement de la phase suspendante et de la suspension, etc. Cette recherche exhaustive vise essentiellement à évaluer l’influence de différents paramètres de formulation et d’essais sur les propriétés rhéologiques des BAP afin de comprendre le comportement à l’écoulement de cette classe de béton. Une approche de prédiction des propriétés rhéologiques des BAP simulés par des suspensions diphasiques, c’est-à-dire composés d’une phase suspendante et inclusions solides, est proposée. L’approche diphasique se heurte généralement à la difficulté de définir la phase suspendante. La première phase du programme expérimental est consacrée à une évaluation de l’applicabilité de la méthode de mortier de béton équivalent (MBE) pour prédire les propriétés à l’état frais des BAP. Les résultats obtenus montrent que cette méthode ne fournit pas une bonne corrélation entre les propriétés à l’état frais des BAP et leur MBE. Ceci est dû, en partie, au fait que seule la surface spécifique des gros granulats soit considérée comme critère pour formuler les mélanges de MBE. En effet, les résultats obtenus montrent que le concept de la pâte en excès doit être considéré pour améliorer les relations entre le BAP et son MBE. Ce concept tient compte du volume et de la compacité des gros granulats dans le béton. Bien que l’utilisation de la pâte en excès améliorer l’approche du MBE, mais résulte en des corrélations complexes et difficilement exploitables pour pouvoir appliquer une approche diphasique afin de prédire les propriétés à l’état frais et rhéologiques des BAP en considérant le MBE comme phase suspendante. Pour pallier à cette difficulté, une investigation plus exhaustive de la pâte-mortier/mortier-BAP est nécessaire afin de mieux comprendre la synergie des différents paramètres de formulation et d’identifier la phases suspendante la plus adéquate pour prédire les propriétés du BAP. La deuxième phase de cette étude porte sur l’évaluation de l’effet des caractéristiques des particules solides sur les propriétés rhéologiques des suspensions en exploitant des modèles analytiques, notamment les modèles de Krieger-Dougherty (KD) et de Château-Ovarlez-Trung (COT). Les résultats obtenus ont permis de mettre en évidence l’effet de la forme et de la granulométrie des particules solides sur les paramètres intrinsèques de ces modèles analytiques. De plus, il est montré que ces paramètres intrinsèques sont considérablement affectés par les paramètres de formulation, le protocole de cisaillement et la concentration de la phase suspendante (i.e. rapport Eau/Liant). Par ailleurs, il est montré que le modèle rhéologique (Bingham ou Herschel Bulkley) choisi pour décrire le comportement de la phase suspendante (pâte) et de la suspension (mortier) est un facteur influent sur les propriétés rhéologiques prédites des suspensions. La troisième phase de cette étude vise l’exploitation des modèles analytiques pour prédire les propriétés rhéologiques tout en identifiant une phase suspendante qui représente le plus fidèlement le BAP. Différentes phases suspendantes (mortier) ont été évaluées, notamment le mortier tamisé, mortier type I et le mortier II. Les corrélations entre les propriétés à l’état frais et rhéologiques des BAP et de différents mortiers ont été établies. De plus, l’effet des paramètres de formulation les plus influents sur les corrélations des propriétés rhéologiques entre les différentes phases ainsi que sur les paramètres intrinsèques des modèles de prédiction ont été mis en évidence. Des modèles sont proposés pour prédire les propriétés rhéologiques des mélanges de BAP en considérant le mortier type II comme phase suspendante.

In this work, microfluidic and millifluidic droplets are utilized to study and control complex fluid behavior with high composition resolution. Different techniques are used on two length scales to create unique approaches towards the same goal of merging droplet-based experiments with classical colloidal characterization experiments. First, a microfluidic dehydrating droplet device is characterized and a procedure established by concentrating a phase separating organic-inorganic system on chip and using geometric calculations to determine composition. The device is then expanded to a more complex, particle-polymer system to investigate suspension stability and interparticle behavior. A model system containing silica particles and PEO polymer is found to transition from a bridging flocculation mechanism to polymer-coated particle jamming based on the mass ratio of polymer to particle. Lastly, a phase separating particle-polymer system consisting of polystyrene particles and hydroxyethyl cellulose is concentrated on-chip. Interparticle interactions are controlled by varying particle size, polymer size, and polymer type and the effects on phase behavior are examined. Droplet experiments are scaled-up to millifluidic droplets and concentration gradients are used to produce high composition resolution in place of time, used in the dehydrating microfluidic experiments. A novel, millifluidic containment device is created to study aggregation and sedimentation in droplets containing carbon black and OLOA surfactant suspended in dodecane. A slow increase in stabilization behavior is observed as opposed to the previously observed sharp “on-off” effect. The droplet production technique is then improved to achieve more complex composition paths and the device is expanded for a small angle neutron scattering (SANS) application. SANS is performed on flowing droplets with varying concentration to map interparticle interactions and phase behavior of complex particulate systems. Feasibility of device is demonstrated and preliminary model systems of silica particles and polymer, salt, and surfactant are analyzed and characterized.

Lorsque des particules actives, des particules pouvant se mouvoir par elles-mêmes, sont mises en suspension dans un fluide, celles-ci peuvent avoir un comportement collectif. Dans ce document, nous présentons des travaux expérimentaux utilisant des Escherichia Coli, une particule biologique, des techniques microfluidiques, ainsi que des simulations numériques. Ceux-ci nous ont permis de caractériser les comportements collectifs de ces nageurs, leur modification en présence d'un cisaillement extérieur ainsi que l'impact de ces comportements microscopiques sur sa viscosité. Nous avons ainsi mis au jour le caractère progressif de l'apparition des mouvements collectifs avec la concentration, l'existence d'un taux de cisaillement critique commun pour les comportements individuels et collectifs des nageurs, ainsi qu'une rhéologie non-newtonienne de ces suspensions. / If we put active particles, ie. motile particles, in suspension into a _uid, collective behaviors can occur. In this document, we present experimental works using Escherichia Coli, a biological particle, micro_uidic devices, and numerical simulations. By these ways, we caracterized these swimmers, their collective motions, the impact of an external shear on their behavior, and rheological behavior of this kind of suspensions. We show that the typical size of these collective motions increases smoothly with the volume fraction, and that a critical shear rate exist and is the same for individual and collective motion under shear. We also show for that bacterial suspensions have a non-newtonian viscosity and describe their rheological behavior.

Les caséines, les protéines les plus abondantes du lait, sont associées sous forme de micelle ayant un rayon moyen de 100nm, pontées par du phosphate de calcium colloïdal (CCP). Lorsque le CCP est retiré par précipitation acide, les micelles se désintègrent formant les caséinates de sodium (NaCas), des particules de 10nm. Les caséines sont très sensibles aux ions calcium et phosphate présents dans certains produits alimentaires qui constituent un levier important dans l’industrie laitière pour contrôler la texture. La viscosité des suspensions de NaCas augmente fortement lorsque la concentration en protéines augmente à cause du remplissage compact par les particules, mais décroît lorsque la température augmente car la fraction volumique efficace des particules diminue. Au-delà d’un ratio critique Ca2+/caséine, les interactions attractives mènent à la formation de microdomaines denses qui diminuent la solubilité et augmententla turbidité. Le phénomène est amplifié lorsque la température augmente et modifie les propriétés viscoélastiques des suspensions de NaCas. En large excès, les ions Na+ entraînent la dissociation des micro-domaines denses par compétition avec les ions Ca2+. Au-dessus de 0.2M de Na+, la viscosité augmente à cause de la déshydratation des protéines (salting-out). L’orthophosphate (Pi) se lie aux protéines en présence de calcium, ce qui conduit à la formation de complexes. En large excès, le Pi se lie directement au calcium et précipite forme de phosphate de calcium ou sous forme de complexes avec les protéines. Lorsque les micelles des caséines sont acidifiées au-dessus de pH 5,2, le phosphateet le calcium solubilisés interagissent avec les protéines lorsque la température augmente, ce qui conduit à une gélification. Cette étude a démontré combien la nature du phosphate et du calcium est fondamentale dans l’organisation des caséines en suspension dense. / In milk, caseins, the main proteins, are associated into a casein micelle (100nm) held together with colloidal calciumphosphate (CCP). When CCP is removed by acid precipitation into sodium caseinate (NaCas), the caseins reassemble into smaller particles, the so-called submicelles (10nm). Caseins are highly sensitive to calcium and phosphate ions,used in most applications. Challenge for dairy industry is to control the texture, mainly determined by protein interactions.The viscosity of dense NaCas suspensions strongly increased with increasing concentration due to jamming of the particles. Increasing the temperature led to a decrease of the viscosity as the effective volume fraction of the particles decreased. When a ratio of Ca2+ is bound by the casein, attractive interactions are introduced and led to the formation of dense micron sized particles that decreased solubility and increased the turbidity. The effect was stronger with increasingtemperature. The visco-elastic properties of NaCas suspensions were also modified. The same behaviour was observed for calcium caseinate suspensions if the ratio of Ca2+ per casein was equal. Large excess of Na+ led to dissociationof the dense protein domains formed by Ca2+ by competiton for specific binding sites of caseins. For increasing the Na+concentration above 0.2M the viscosity increased by decreased hydration of the protein. Orthophosphate (Pi) was bound to the caseins with Ca2+ leading to the formation of complexes. Large excess of Pi competed with Ca2+. The precipitation of the caseins and large calcium phosphate particles were formed. When casein micelles are acidified above pH 5.2, calcium and phosphate are solubilized and interact with casein leading to the formation of a gel. This study showed how calcium and phosphate of different origins are fundamental in the organization of caseins in dense suspensions.

Dispersed multiphase flows occur in many biological, engineering and geophysical applications. Understanding the behavior of suspensions is a difficult task. In the present work, we numerically study the behavior of suspensions of finite-size rigid particles in different flows. Firstly, the sedimentation of spherical particles larger than the Taylor microscale in sustained homogeneous isotropic turbulence and quiescent fluid is investigated. The results show that the mean settling velocity is lower in an already turbulent flow than in a quiescent fluid. We also investigate the settling in quiescent fluid of oblate particles. We find that at low volume fractions the mean settling speed of the suspension is substantially larger than the terminal speed of an isolated oblate. Suspensions of finite-size spheres are also studied in turbulent channel flow. First, we change the solid volume and mass fractions, and the solid-to-fluid density ratio in an idealized scenario where gravity is neglected. Then we investigate the effects of polydispersity. It is found that the statistics are substantially altered by changes in volume fraction. We then consider suspensions of solid spheres in turbulent duct flows. We see that particles accumulate mostly at the corners or at the core depending on the volume fraction. Secondary motions are enhanced by increasing the volume fraction, until excluded volume effects are so strong that the turbulence activity is reduced. The inertial migration of spheres in laminar square duct flows is also investigated. We consider semi-dilute suspensions at different bulk Reynolds numbers and duct-to-particle size ratios. The highest particle concentration is found around the focusing points, except at very large volume fractions. Finally we study the rheology of confined dense suspensions of spheres in simple shear flow. We focus on the weakly inertial regime and show that the effective viscosity varies non-monotonically with increasing confinement. / <p>QC 20171117</p>

The purpose of this study was to determine if character education programs impact the suspension rates of students from regular instructional public elementary schools in Texas. The data was also examined to determine if the number of years since a school's implementation of a character education program has an impact on the effectiveness of the programs as measured by the suspension rates of students from school. Finally, the study sought to determine if the socio-economic status of the schools has an impact on the effectiveness of character education programs as measured by the student suspension rates. A random sample of 135 regular instructional public elementary schools in Texas was collected. The principal of each school completed a questionnaire that was used to sort schools into three groups: schools with "direct" character education programs, schools with "indirect" character education programs, and schools that have implemented no type of character education program. A two-year history of suspensions was obtained for each school. The data was analyzed using one-way and two-way ANOVAs. The results of the analyses indicated that the implementation of character education programs, no matter what type, did not produce statistically significant differences in student suspension rates from school. Furthermore, the data revealed that neither the number of years since the implementation of the character education programs nor the socio-economic status of the schools had an impact on the effectiveness of the character education programs as measured by the student suspension rates from school.

Diploma thesis is focused on development of method for preparation individualized bioscaffolds prepared by milling of HA foam prepared by gel casting method and consolidated via epoxy curing reaction. Diploma thesis continues in bachelor thesis Modern processing methods of porous bioceramics. Literature search is filled in the newest knowledge from the field of bioactivity enhancement of scaffolds. Experimental part of diploma thesis described development of system for individualized scaffold manufacturing from HA suspension preparation, preparation of ceramic blocks used as material for machining to final blocks machining. Pressure strength of foam were evaluated, too. Chosen samples were coated with calcium polyphosphate coating for biological response enhancement. Coated samples were given for in-vivo test to partner university in Beijing under the terms of project FP7-NMP-2013-EU-China: "Bioscaffolds"

Les travaux numériques et expérimentaux de cette thèse contribuent à une meilleure compréhension de la dynamique de grosses particules dans un écoulement turbulent. Un premier volet m’a permis de quantifier leur mouvement relatif au fluide, ainsi que leur influence locale sur l’écoulement turbulent. Dans un second volet, j'ai trouvé que l'effet collectif des particules est d'atténuer l’amplitude des fluctuations turbulentes. En revanche, celles-ci n’ont pas d’influence sur les propriétés statistiques fines de l’écoulement. Aussi, ces mesures suggèrent l’existence d’une transition de phase dans les grandes échelles de l’écoulement au-delà d’un seuil critique du nombre de particules. / The numerical and experimental work of this thesis contribute to a better understanding of the dynamics of large particles in a turbulent flow. The first part allowed me to quantify their relative motion to the flow and their local influence on the surrounding flow. In a second part, I found that the collective effect of particles is to reduce the amplitude of turbulent fluctuations. In revanche, they have no influence on the fine statistical properties of the flow. Also, these measurements suggest the existence of a phase transition in the larger scales of the flow beyond a critical threshold of the number of particles.

Nuclear Magnetic Resonance is used for the determination of the properties of porous media in Geophysics and oil exploration. As it stands, there is a challenge in understanding the connection between the times measured in Free Induction Decay Nuclear Magnetic Resonance experiments and the shape of samples. In this work, suspensions and watersaturated densely-packed porous media with the volume fraction of the glass solid phase in the range from 10–4 to ∼1 are found to exhibit FID decay rates proportional to the square root of the volume fraction of the solid phase of the samples. A model of spheres in liquid is proposed for the description of such behavior.