Rozprawy doktorskie na temat „Rheology”

This thesis compares the rheology of unspun silk from both the spider and the silkworm in order to understand their evolutionary constraints and to turn these into design criteria for artificial silks.

I describe an experimental apparatus used to perform deformation experiments relevant to volcanology. The apparatus supports low-load, high-temperature deformation experiments under dry and wet conditions on natural and synthetic samples. The experiments recover the transient rheology of complex (melt ± porosity ± solids) volcanic materials during uniaxial deformation. The key component to this apparatus is a steel cell designed for high-temperature deformation experiments under controlled water pressure. Experiments are run under constant displacement rates or constant loads; the range of accessible experimental conditions include: 25 - 1100 °C, load stresses 0 to 150 MPa, strain rates 10⁻⁶ to 10⁻² s⁻¹, and fluid pressures 0-150 MPa. I present a suite of high-temperature, uniaxial deformation experiments performed on 25 by 50 mm unjacketed cores of porous Φ∼0.8) sintered rhyolitic ash. The experiments were performed at, both, atmospheric (dry) and elevated water pressure conditions (wet). Dry experiments were conducted mainly at 900 °C, but also included a suite of lower temperature experiments at 850, 800 and 750 °C. Wet experiments were performed at ∼650 °C under water pressures of 1, 2.5, 3, and 5 MPa, and at a fixed PH2O of ∼2.5 MPa for temperatures of ∼385, 450, and 550 °C. During deformation, strain is manifest by shortening of the cores, reduction of porosity, flattening of ash particles, and radial bulging of the cores. The continuous reduction of porosity leads to a dynamic transient strain-dependent rheology and requires strain to be partitioned between a volume (porosity loss) and a shear (radial bulging) component. The effect of increasing porosity is to expand the window for viscous deformation for dry melts by delaying the onset of brittle deformation by ∼50 °C (875 °C to 825 °C). The effect is more pronounced in hydrous melts (∼0.67 — 0.78 wt. % H₂0) where the viscous to brittle transition is depressed by ∼140 to 150 °C. Increasing water pressure also delays the onset of strain hardening due to compaction-driven porosity reduction. These rheological data are pertinent to volcanic processes where high-temperature porous magmas I liquids are encountered (e.g., magma flow in conduits, welding of pyroclastic materials).

Rheological behavior of two commercial brands of stirred yogurt were investigated using a Haake RV 20 rotational viscometer. For samples from both brands, the upward shear-rate flow behavior generally followed the Herschel-Bulkley model and the downward flow curves were linear. They demonstrated progressive structural degradation with repeated shearing. In the steady shear runs, all samples exhibited apparent thixotropic behavior and did not attain the equilibrium condition even after 60 min of continuous shearing. The time-dependent stress decay behavior of all samples were accurately described by Weltman's logarithmic time model. The rheological properties of both yogurt brands were qualitatively similar. Both Arrhenius and Turian models were found suitable to assess the temperature influence in the range 10-25$ sp circ$C.
The influence of pectin (0.0 to 0.5%) and fruit concentrates (raspberry and strawberry) (64$ sp circ$B, 0 to 10%) on the rheology of stirred yogurt were evaluated. The influence of storage time at 2$ sp circ$C up to a period of four weeks on the rheological properties of the two brands were evaluated.

The rheology of caramel was determined as a function of processing temperature and hydrocolloid additions. As the processing temperature increased the water content decreased and the caramel viscosity increased. X-ray diffraction showed that although crystalline fat was present, for the most part the sugars were in the amorphous state. The exception was the lowest water content caramel (7.9% water w.w.b.) which had been processed to a temperature of 122ºC. This had a small amount of crystalline fructose. Caramel rheology was assessed by rotational and capillary rheometry. Rotational rheometry gave information on the steady shear viscosity, the dynamic parameters (storage and loss moduli and related functions) and the creep compliance and recovery response. Capillary rheometry gave shear viscosities at high shear rates and an extensional viscosity. It was found that caramel without added hydrocolloids had behavior which was close to a Newtonian liquid. The only exception to this was the values obtained for the Trouton ratio which ranged from 10 to 40. This was considerably higher than the value of 3 for a Newtonian fluid and may reflect the difficulties in making measurements on these relatively low viscosity systems in the capillary rheometer. The viscosities obtained from steady shear, oscillation and creep were combined and three approaches were used to model the data as a function of measurement temperature and water content. An empirical statistical model using a second order polynomial, an Arrhenius fit and a Williams Landel Ferry (WLF) model. The former and the latter gave a good fit to the data although the constants used in the WLF model varied with the water content of the caramel. Arrhenius plots showed curvature particularly at low water contents. Incorporation of the hydrocolloids carrageenan and gellan gum into the caramel made the material non-Newtonian and elastic. For carrageenan incorporation in particular the Trouton ratio increased with carrageenan concentration reaching a value ~500 at a strain rate of 100s-1 for the caramel containing 0.2% carrageenan It was demonstrated that incorporation of carrageenan could be used to prevent cold flow in caramels processed at relatively high water contents. Glass transition temperatures were measured by differential scanning calorimetry and calculated from the temperature dependence of the shift factors used to superimpose the oscillatory rheological data. Generally there was agreement between the two approaches although for some gellan gum containing samples the rheological Tg was about 10ºC higher than the DSC value. Fragility calculated from the WLF constants for caramel was high as has been reported for sugars. The Tg for both caramel and sugar water mixtures calculated using the Couchman-Karastz equation in the water content of interest (9-15% w.w.b.) was some 30-40°C higher than measured. It is suggested that this disagreement could be related to the high fragility of the sugar water systems. Isoelectric point measurements using a streaming potential technique was shown to give information on the extent of the Maillard reaction and the presence of hydrocolloids.

The behaviour of paste is complex.  It has many unusual properties that do not fit with other engineering materials.  These can be linked to the volume effects that occur as the material is sheared. A multi-phase model based on a soil mechanic approach has been developed to consider the particle, liquid and gas components.  The volume is allowed to change during shearing and links these effects to the shear stress through pore fluid pressure and surface tension.  There is also a movable reference strain to allow the model the ability to simulate both cyclic and monotonic deformations in one system. Constrained pressure tests were conducted over a fixed strain amplitude cyclic deformation.  These were conducted in a series to consider the effects of strain rate, amplitude and pressure in a paste.  They were then analysed visually and statistically to find which of the variables were significant to the stress-strain response in paste. A further series of tests carried out with an increasing amplitude cyclic test.  This test was simpler but allowed a series of different pastes to be analysed without attempting to control the pore pressure in the materials.  A number of different responses were noted and a fuller picture of paste reaction was developed. Finally, the material model was matched to physical tests to evaluate the model’s ability to fit to different paste responses.  This was completed successfully with the use of an optimisation algorithm.

Thesis (MScEng)--Stellenbosch University, 2003.
ENGLISH ABSTRACT: Desired behaviour of paint during processing, storage, application and after application is of great importance in the coatings industry. Rheology (the study of flow and deformation behaviour) is used as a method to investigate the behaviour of the flow and deformation properties of the paint during these stages. Some of the more important phenomena that can occur during these stages, which were examined rheologically, are: 1. The rheological behaviour of certain complex raw materials during processing - vesiculated beads suspensions 11. The paint behaviour during storage - in-can stability, e.g. phase separation and sedimentation of particles; Ill. The paint during application - ease of application, spatter, etc.; IV. The paint behaviour after application - sag, layer thickness, levelling (ability to hide brush marks), etc. A rheometer was used to obtain rheological curves from a paint sample (± 1 ml). Correct interpretation of these curves, which display rheological properties of the sample such as the viscosity, shear stress, structural strength and many more, produced information about the properties mentioned in i, ii, iii and iv above. It was found that the rheological data correlated well with empirical tests carried out in the laboratory for spatter, sag, levelling behaviour and in-can stability of the paint. A wide variety of paints were studied ranging from tough/durable outdoor paints to smooth/velvety indoor paints. The rheological behaviour explained the specific end-use properties of the paints. Paints from two different companies were compared on a rheological basis. In some cases large differences in rheological behaviour were observed. Rheology modifiers were tested on a new paint. It was found that specific rheology modifiers could be incorporated into the formulation to give the specific rheological behaviour required. Rheological modelling was performed and it was found that the flow behaviour of paint cou1d be modelled accurately with existing viscosity models (Ostwald/de Waal, Bingham, Casson, Herschel-Bulkley, Cross and Philips-Deutsch). Other rheological properties of paint were also modelled successfully with a simple linear regression model. Rheology was also used as a method to examine the flow and deformation properties of vesiculated beads, a component of paint with very complex rheology. The most important factors that influence the rheological behaviour of the vesiculated beads were determined. It was found that the type of manufacturing process for the beads affected the rheological behaviour. The effect of the raw materials used to manufacture the vesiculated beads were rheologically determined.
AFRIKAANSE OPSOMMING: Dit is baie belangrik dat verf die gewenste gedrag moet toon tydens berging, vervaardiging, tydens aanwending en direk na aanwending. Reologie (die studie van vloei- en vervorming) word gebruik as a metode om die vloei- en vervormingseienskappe van verf gedurende bogenoemde stadia te ondersoek. Sommige van die belangriker verskynsels wat gedurende hierdie stadia kan plaasvind, is d.m.v reologiese toetse ondersoek. Die verskynsels is as volg: i. Die reologiese gedrag van komplekse grondstowwe soos gevesikuleerde partikel suspensies. ll. Verfgedrag tydens berging - stabiliteit van verf in die blik, bv. faseskeiding en sedimentasie van partikels lll. Verfgedrag tydens aanwending - gemak van aanwending, spatsels IV. Verfgedrag direk na aanwending - afsakking, dikte van verflaag, vloei-eienskappe 'n Reometer is gebruik om die reologiese kurwes te bepaal deur gebruik te maak van ± 1 ml monster. Korrekte interpretasie van hierdie kurwes, wat onder meer eienskappe soos viskositeit, spanning en struktuursterkte insluit, lei tot inligting wat die verskynsels in i, ii, iii en iv kan verklaar. Daar is gevind dat inligting wat verkry is i.v.m die verskynsel van spatsels, afsakking, vloei en die stabiliteit van verf in die blik, goed korreleer met empiriese toetse wat in die laboratorium uitgevoer is. 'n Groot verskeidenheid van verwe, wat wissel van duursame/sterk buitemuurse verf, tot fluweelsagte binnenshuise verf, isondersoek. Die reologiese toetse het daarin geslaag om die eienskappe van die eindproduk suksesvol te verduidelik. Verf van twee verskillende maatskappye is ook met mekaar vergelyk op 'n reologiese grondslag. Daar is by sommige van die verwe aansienlike verskille in die reologiese gedrag gevind. 'n Nuwe verf is gebruik om die uitwerking van reologie modifiseerders te ondersoek. Daar is gevind dat daar spesifieke reologie modifiseerders bestaan wat unieke reologiese gedrag verseker. Reologiese modellering is gedoen op verf en daar is gevind dat die vloeigedrag van die verf akkuraat gemodelleer kan word deur van die bestaande viskositeitsmodelle gebruik te maak (Ostwald/de Waal, Bingham, Casson, Herschel- Bulkley, Cross en Philips-Deutsch). Ander reologiese eienskappe is gemodelleer deur gebruik te maak van eenvoudige regressie modelle. Daar is ook van reologiese tegnieke gebruik gemaak om die vloei en vervormingseienskappe van gesuspendeerde gevesikuleerde partikels, wat as 'n grondstof vir verf gebruik word, te ondersoek. Die belangrikste faktore wat die reologiese gedrag beïnvloed het, was onder meer die verskillende prosesse waarmee die gevesikuleerde partikels vervaardig is. Die effek van sekere van die grondstowwe wat gebruik word om die gevesikuleerde partikels te vervaardig, is ook reologies ondersoek.

Caramel is a mixture of sugars, milk proteins, fat and water cooked at high temperatures to initiate Maillard reactions. We study caramels as ‘active emulsion-filled protein gels’, in which fat droplets are chemically-bonded to a background gel matrix of cross-linked proteins in a concentrated aqueous sugar solution. A ‘caramel region’ in composition space is delimited by the varying the four ingredients; sugar, milk protein, fat and water. The boundaries of the composition space define various modes of ‘failure’. Boundaries are determined for transitions to toffee and emulsification failure leaking out of the caramel, and protocol dependent failures, scum formation during the cooking step and subsequent boil over or the formation of a ‘creme Chantilly. Oscillatory rheology within the caramel region reveals that we can superpose the mechanical spectra of all caramels into a single pair of G'(ω),G''(ω) master curves using time-composition superposition (tCS) over 12 decades of frequency, so that all caramels are instances of an underlying ‘universal material’. The master curve is an example of a very lightly cross-linked amorphous polymer, a weak rubber. Utilising the cross-over point of G'(ω) and G''(ω) as a common point to compare caramel master curves the viscous and elastic dependency of caramel is determined and linked to the caramels ingredients. Viscosity is dependent on the aqueous sugar content and the elastic dependency on protein content. This insight constrains the molecular mechanisms for structure formation, and implies that measuring a couple of parameters suffices to predict the rheology of caramels over 12 orders of magnitude in frequency.

Polystyrene latices of particle diameter 0.97 ~, 1.41 ~ and 1.92 ~, at an electrolyte concentration of 0.5 mol dm- 3 sodium chloride, were' sterically stabilised by the adsorption of a monolayer of a monodisperse nonionic surface active agent, C12E6• Optical microscopy showed that the resultant systems were weakly flocculated, with only slight agitation required to destroy the flocs. Calculations showed that the van der Waals attractive potential dominated the highly screened electrostatic repulsive potential; the particles were prevented from coagulating into the primary minimum through the presence of the steric barrier. Potential energy well depths of 7 - 15 kT were obtained. Rapid sedimentation of the systems occurred by consolidation of r..he aggregated structure after an induction period which increased with increasing volume fraction to give a final sediment volume fraction of approximately 0.4 - 0.45. Constant stress viscometry demonstrated that the suspensions were shear thinning with a limiting Newtonian viscosity at low stresses. At high stresses the viscosity was similar to that expected for a dispp.rsion of hard spheres as calculated from Krieger's equation~2 Shear wave propagation experiments were performed to measure the high frequency limit of the shear modulus as a function of volume fraction. The values obtained were compared with a theoretical model due to Zwanzig and Mountain79 and based on a statistical mechanical description of the microstructure combined with the pair interaction potential of the particles. Parameters required for the model were the suspension volume fraction, the Stern potential, the Hamaker constant and the extent of the adsorbed layer, all of which were determined independently of the rheological measurements. Good agreement was obtained between theoretical and experimental data when using a Barker Henderson perturbed hard sphere potential model to calculate the pair distributionfunction. The model thus provided a strong test of the use of liquid state theory for the prediction of the transport properties of colloidal suspensions. Predictions of the zero shear viscosity were made using a similar model.

Thesis (Honors paper)--Florida State University, 2008.
Advisor: Dr. Subramanian Ramakrishnan, Florida State University, College of Engineering, Dept. of Chemical Engineering. Includes bibliographical references.

In recent years, high-resolution topographic images from Mars’ surface as well as mineralogical and chemical data, have rapidly become more accessible. Martian volcanic landforms are characterized by giant low slope shield volcanoes, abundant lava flood plains and long lava flows. In-situ rock analysis and remote sensing spectroscopy reveal mainly basaltic compositions with particularly high iron concentrations, distinct from terrestrial basalts. As yet, very little is known about the rheological properties of such iron-rich Martian magmas that are essential to understand magmatic processes. Understanding the chemical and physical contributions to lava rheology is fundamental to provide constraints on magma ascent and lava flow emplacement that shaped the volcanic landforms on Mars. This study provides an experimental investigation of the rheological properties of Martian lavas and discusses the diversity of compositions in terms of lava viscosity / flow morphology relationship. The effect of iron, and its redox state on silicate melt viscosity is experimentally investigated and the viscosities of five synthetic silicate liquids having compositions representative of the diversity of Martian volcanic rocks were measured under controlled ambient oxygen fugacity. The results highlight the low viscosity of the iron-rich Martian melts that is consistent with viscosity values derived from morphological observations. A solidified lava flow on Earth was studied by combining analyses of remote sensing images (as commonly done on Mars), as well as experimental investigations of the rheological properties of the sampled rocks, in order to describe the viscous behavior of lava as emplacement, cooling, and crystallization occur. We show that a cooling-limited basaltic flow seemingly stop flowing when it reaches a critical viscosity value that is function of crystals content and shapes. As a result, the lava apparent viscosity appears to be largely influenced by the details of the crystallization sequence and is not uniquely and simply related to the bulk chemical composition of the erupted material. Variation of the chemical evolution of Martian primary mantle melts through the volcanic history is not large to produce an significant shift of the viscosity range that could be observed them from their morphologies. Low apparent viscosities inferred from lava flow morphology on Mars may in turn be attributed to lavas with primary mantle melt composition crystallizing high proportion of olivine and possibly forming spinifex textures. Higher viscosity values derived from the morphology are compatible with mildly alkaline or trachybasalts and do not necessarily imply the occurrence of silica-rich lavas.
Über die letzten Jahre sind hochauflösende topographische Bilder der Oberfläche des Mars, sowie chemische und mineralogische Daten der Marsgesteine zunehmend verfüg- bar geworden. Die vulkanischen Formationen des Mars beinhalten gigantische Schild- vulkane flacher Ausprägung, grosse Flutbasaltebenen und weitfliessende Lavaströme. In- situ Analysen der Mars Gesteine und “Remote Sensing Spectroscopy“ zeigen grösstenteils basaltische Zusammensetzungen, jedoch mit besonders hohem Eisengehalt, der Mars- gesteine von terrestrischen Proben unterscheidet. Bis dato sind die rheologischen Eigen- schaften dieser eisen-reichen Mars Magmen wenig erforscht. Das Verständnis der physiko- chemischen Parameter, die die Lava Rheologie beeinflussen, ist jedoch fundamental, um Magmaaufstieg und die Ablagerung von Lavaströmen auf dem Mars zu verstehen. In dieser Studie wurden die rheologischen Eigenschaften marsianischer Laven experi- mentell untersucht und die Variabilität der natürlich vorkommenden Zusammensetzungen in Beziehung zu Lava-Viskosität und Lava-Morphologie gesetzt. Der Effekt von Eisen und seines Redox Zustandes auf die Viskosität von Silikatschmelzen wurde experimentell untersucht. Unter kontrollierten Sauerstofffugazitäten wurden die Viskositäten von fünf synthetischen Silikatschmelzen untersucht, deren Zusammensetzun- gen repräsentativ für die Spannbreite der Zusammensetzungen der vulkanischen Gesteine des Mars ist. Die niedrige Viskosität der eisenreichen, marsähnlichen Schmelzen ist kon- sistent mit den Viskositätswerten, die durch morphologische Analysen bestimmt wurden. Als terrestrisches Analog wurde ein erkalteter Lavastrom mit Hilfe von fernerkundlichen Bildern, die in der gleichen Weise für Mars angewendet werden, sowie Messungen der Rheologie an Gesteinsproben dieser Lava untersucht, um Änderungen in der Viskosität während der Ablagerung, des Abkühlens und der Kristallisation zu charakterisieren. Laut unserer Ergebnisse wird ein durch Abkühlen limitierter basaltischer Lavastrom aufgrund von erhöhtem Kristallgehalt und als Funktion von Kristallhabitus gestoppt. Die appar- ente Viskosität scheint daher grösstenteils von der Kinetik der Kristallisatiosnsequenz beeinflusst und weniger von der Gesamtzusammensetzung des eruptierten Materials. Als Folge hätte die Variabilität in der Zusammensetzung der primären, marsianischen Man- telschmelzen über die vulkanische Historie keinen signifikanten Effekt auf die apparente Viskosität, die durch Lava-Morphologie-Analysen bestimmt wird. Niedrige apparente Viskositäten aus diesen Morphologie-Analysen erklären sich dadurch hauptsächlich als Folge von primären Mantelschmelzen, die einen hohen Anteil von Olivin kristallisieren und möglicherweise Spinifex Texturen ausbilden. Wenn Morphologieanalysen höhere Viskositäten ausgeben ist dies kompatibel mit schwach alkalinen Basalten oder Trachy- basalten, bedeutet jedoch nicht notwendigerweise das Vorkommen felsischer Laven.
Ces dernières années, des nouvelles données satellites de la surface de Mars de haute résolution (topographiques ainsi que minéralogiques et chimiques), sont devenues accessi- bles à la communauté scientifique. Sur Mars, les paysages volcaniques sont caractérisés par des volcans boucliers géants à pentes faibles, des plaines de lave et des longues coulées de lave. L’analyse des roches in situ et par spectroscopie orbitale révèlent que la composition des roches est essentiellement basaltique contenant une quantité de Fer particulièrement élevée, clairement distincte des basaltes terrestres. À ce jour, les propriétés rhéologiques des magmas martiens riches en Fer, qui sont essentielles pour comprendre les processus magmatiques, n’ont pas été étudiées en détails. Définir comment la teneur en Fer con- trôle la rhéologie des laves est fondamental pour comprendre l’ascension des magmas et interpréter la mise en place des coulées de lave qui façonnent les paysages volcaniques sur Mars. Cette thèse fournit une étude expérimentale des propriétés rhéologiques des laves martiennes et discute de la diversité des compositions en termes de relation entre viscosité et morphologie des coulées. L’effet du Fer et son état d’oxydo-réduction sur la viscosité des liquides silicatés sont étudiés expérimentalement et les viscosités de cinq laves ayant des compositions représen- tatives de la diversité des roches volcaniques martiennes ont été mesurées en fonction de la température. Les résultats mettent en évidence la faible viscosité de ces liquides martiens riches en fer, ce qui est compatible avec la viscosité déduite des observations morphologiques. Afin de décrire le comportement visqueux d’une coulée de lave pendant sa mise en place (refroidissement et cristallisation), une coulée terrestre a été étudiée, en combinant l’analyse des images de télédétection (comme on le fait sur Mars) et l’étude expérimentale des propriétés rhéologiques des roches échantillonnées. Nous montrons que la forme des coulées basaltiques qui ont cessé d’avancer à cause de leur refroidissement, atteignent une limite rhéologique qui dépend des détails de la séquence de cristallisation et de la forme des cristaux. Leur viscosité apparente n’est pas uniquement et simplement liée à la composition chimique de la lave. Ainsi, l’évolution chimique des liquides pri- maires issus de la fonte partielle du manteau martien à travers l’histoire volcanique de Mars n’a pas d’effet significatif sur la viscosité apparente déterminée par la morphologie des coulées. Les faibles viscosités apparentes déduites de la morphologie des laves sur Mars peuvent être attribuées à des compositions de liquides primaires qui cristallisent des olivines en forte proportion et pouvant former une texture spinifex. Les viscosité plus élevées dérivées de la morphologie sont elles compatibles avec des basaltes légèrement alcalins ou trachytique et n’impliquent pas nécessairement la présence de laves riches en silice de type andésitique.

Many different physical systems, such as granular materials, colloids, foams and emulsions exhibit a jamming transition where the system changes from a liquid-like flowing state to a solid jammed state as the packing fraction increases. These systems are often modeled using soft-core particles with repulsive contact forces. In this thesis we explore several different dynamical models for these kinds of systems, and see how they affect the behavior around the jamming transition. We investigate the effect of different types of dissipative forces on the rheology, and study how different methods of preparing a particle configuration affect their probability to jam when quenched. We study the rheology of sheared systems close to the jamming transition. It has been proposed that the athermal jamming transition is controlled by a critical point, point J, with certain scaling properties. We investigate this using multivariable scaling analysis based on renormalization group theory to explore the scaling properties of the transition and determine the position of point J and some of the critical exponents.

This thesis describes a novel experimental system for the study of polymer flow in a cross-slot using a Cambridge Multi-Pass Rheometer (MPR). Cross-slot flow is capable of generating pure rotation-free extensional flow and the rheological information from the MPR is in a format which can easily be compared with the results of numerical simulations. Using only a small quantity of polymer, this technique provides a quantitative test of the performance of constitutive equations and numerical solvers in extensional flow. The cross-slot apparatus was developed and experiments were studied principally using optical birefringence. It was found that the different shapes of the birefringence patterns observed reveal useful information about the rheology and molecular structure of the polymers. For unbranched low molecular weight polymers at low extension rates, an almost Newtonian response was observed, generating a symmetric fringe pattern. as the level of branching, the molecular weight or the extension rate increased, the fringe pattern became more elongated, suggesting stronger viscoelastic effects. For highly branched polymers a very localised stress concentration was observed along the exit symmetry plane. Pioneering experiments with monodisperse polymer have been particularly revealing – a flow transition is observed at extension rates approximately equal to the inverse of the relaxation time. At low flowrates the response was almost Newtonian, but for extension rates above the inverse of the relaxation time a non-homogeneous stress pattern was observed suggesting possible melt fracture of the fluid in the continuum. The experiments have been compared with numerical simulations using generalised Newtonian, integral-Wagner, Rolie-Poly and pom-pom constructive equations. It has been found that the viscoelastic numerical simulations revealed many of the important features observed from the experiments. However, the quantitative value for stress predicted in some case was higher than the measured value.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Este trabalho trata do escoamento na escala das gotas e da Reologia de emulsões diluídas. Técnicas analíticas e numéricas são empregadas na solução do problema. Nas vizinhan»cas das gotas o escoamento pode ser considerado livre de efeitos de inércia e conseqüentemente as equações governantes são as equações de Stokes. Esse limite é conhecido na literatura como Microhidrodinâmica. O campo de velocidade e de tensão sobre a superfície das gotas é calculado. Um processo de média espacial é realizado em um volume representativo da suspensão tal que a mesma possa ser estudada como um ruido contínuo equivalente. Métodos assintóticos baseados em aproximações de pequenas deformações das gotas são empregados para produzir teorias de primeira e segunda ordens da razão de viscosidade. Uma extensão da teoria para emulsões diluídas polidispersas é desenvolvida. Uma teoria viscoelástica quasi-linear é construída para emulsões diluídas de alta razão de viscosidade em cisalhamento oscilatório. Em regimes de grandes deformações utiliza-se o Método Integral de Contorno para determinar-se a forma da gota e o campos de velocidade sobre a mesma. O método é descrito em detalhes, tanto do ponto de vista teórico como de sua implementação numérica. A validação da metodologia numérica é feita utilizando resultados teóricos e experimentais, disponíveis na literatura. A reologia da emulsão é estudada em escoamentos de cisalhamento simples, oscilatório, pura extensão e cisalhamento quadrático (escoamento de Poiseuille). Os resultados numéricos para cisalhamento simples são utilizados para determinar constantes materiais da teoria assintótica de segunda ordem para a tensão. Limites não-lineares de escoamento em regimes de razões de viscosidade moderadas para os cisalhamentos simples, oscilatório e quadrático são estudados
This work deals with the flow in the scale of the drops and the Rheology of diluted emulsions. Analytic and numerical techniques are employed in order to solve the problem. In the drop neighborhoods the flow may be considered as free of inertia effects and consequently governed by Stokes equations. In the literature this limit is known as Microhydrodynamics. The flow field and the stress tensor on the drop surface are calculated. A spatial mean process was taken, in a representative suspension volume, in order to study the emulsion as an homogeneous and continuous fluid. Asymptotic methods based in small drop deformation approximation are used to produce first and second orders theories which the parameter is the viscosity ratio. An extension of these theories for polydisperse diluted emulsion is developed. A quasi-linear viscoelasticity theory is constructed for diluted emulsion of high viscosity ratios in oscillatory shear flows. In the regimes of large deformations, the velocity and the stress on the particles are evaluated by a numerical procedure based on the Boundary Integral Method for deformable drops. The theoretical and numerical aspects of the Boundary Integral Method are described in details. The code is validated by comparison the numerical results with the experimental data presented in the literature, and also by comparison with the theoretical results of small deformation. The emulsion rheology is studied in simple shear, oscillatory shear, extensional and also in pressure driven flows. The numerical results are used to determine material constants of the stress theory of the second order. Non linear flow regimes of moderate viscosity ratios in simple shear, oscillatory shear and pressure driven flows are also studied.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 107-122).
Protein-surfactant mixtures appear in many industrial and biological applications. Indeed, a fluid as vital as blood contains a mixture of serum albumin proteins with various other smaller surface-active components. Proteins and other surface active molecules are often adsorbed at an air-liquid or liquid-liquid interface due to favorable thermodynamics, and these interfaces play a role in such diverse fields as stabilizing foams and emulsions, controlling high speed coatings, the blood clotting process, designing synthetic replacements of biological fluids, etc. It is thus important to understand the interfacial behavior of protein-surfactant mixtures, especially the role it can play in bulk measurements of material properties. A complete description of the dynamics of these multi-component systems is still elusive. In this thesis, a comprehensive study of the rheology of a model globular protein solution is described. In conventional bulk rheological studies of globular protein solutions a yield-like behavior and shear thinning in the viscosity at low shear rates is observed, even for concentrations as low as 0.03% by weight. Typical explanations for this yield stress involve the introduction of long range colloidal forces that are stronger than electrostatic forces, and which stabilize a colloidal structure formed by the protein molecules. However, evidence for this structure from small angle X-ray scattering and small angle neutron scattering is lacking. In the first part of this thesis, it will be shown using interfacial steady and oscillatory shear experiments how the yield-like behavior observed in bulk rheology in fact arises out of a purely interfacial effect. We show that the yield-like behavior and shear-thinning observed in bulk rheology can be modeled by treating the interfacial layer of the adsorbed protein as a pure plastic material that yields at a critical strain. This model also accounts for the geometric dependence seen in bulk rheology experiments. The second part of this thesis investigates the rheological consequences of adding low molecular weight surfactants to globular protein solutions. Because non-ionic surfactants compete for the interface with the protein molecules, the resulting dynamics at the fluid interface can be complex. In addition to steady and oscillatory interfacial shear rheology, a new phenomenon called interfacial creep ringing-a term used to denote the periodic oscillations arising from the coupling between instrument inertia and interface elasticity-arises. It is demonstrated how these damped inertioelastic oscillations can be used to rapidly estimate interfacial viscoelastic moduli and also study the effect of the addition of non-ionic surfactants to globular protein solutions. We show that exploiting the interfacial creep ringing technique is useful as a way to rapidly determine the effects of interfacial viscoelasticity. It is also observed that increasing the concentration of the competing surfactant leads to progressively decreasing ringing frequencies and amplitudes, until visible ringing completely disappears beyond a certain concentration. Finally, we indicate future avenues of work including surface particle tracking to study these complex dynamics of protein surfactant mixtures.
by Aditya Jaishankar.
S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (p. 99-107).
We investigated the extensional properties of wheat flour dough on the Filament Stretching Rheometer (FISER), in which the sample approaches uniform uni-axial extension flow at a constant strain rate over a large portion of the experiment, thereby allowing us to directly probe the transient material function characterizing the behavior of dough in extension. The large dynamic range of this Rheometer permitted us to investigate the visco-elastic nature of the dough well into the baking/proofing range. Special experimental protocols and modifications to the rheometer fixtures were designed and built to overcome problems in sample preparation. Parameters such as water content, base flour type and mixing conditions were varied to determine their respective effects on the extensional properties. Ultimately we would like to develop a constitutive equation describing the evolution of stress during extension and arrive at a model for the stability against rupture in these doughs.
(cont.) This will form the basis for developing protocols to map results from the true uni-axial extension experiments onto empirical measurements obtained from existing and widely utilized industrial standard testing devices. As an example in this first stage, we focused on the Mixograph, which is a widely accepted method of testing dough in the food industry, and considered how its output can be related to the true material functions generated in filament stretching rheometry.
by Shen Kuan Ng.
S.M.

The interaction of carbon black with an acrylic resin in aqueous solution has been investigated by rheology. Two carbon blacks Raven L and Raven M, with similar particle size and surface characteristics but quite different particle morphologies, have been examined. In the absence of polymer, stable aqueous dispersions could not be obtained. Stable dispersions could be obtained however upon addition of polymer to a level corresponding to a ratio of 50mg of polymer per 13m2 of surface area (i.e.l5wt% particles). These stable dispersions exhibit flow typical of concentrated dispersions - Newtonian behaviour up to some apparent "yield" or critical value. Above which shear thinning is observed. This critical stress increases with increasing polymer concentration. At low polymer concentrations, the dispersions are predominantly viscous at low shear stresses. The phase angle decreases significantly over a narrow shear stress range and the rheology tends to more elastic behaviour. At higher shear stresses, the dependence on particle morphology is weak. Furthermore, increasing the pH of the aqueous dispersions has little effect, but changing the adsorbent does alter the rheology somewhat. In addition to Raven L and Raven M, other carbon blacks were also investigated in which the surface chemistry had been modified by ozonolysis. In addition to aqueous systems, a selection of oil based systems have also been investigated. Here, four carbon blacks were used with a bitumen binder: the low-medium structured fine particle (Raven L), the medium-high structured fine particle (Raven M), a low-medium structured coarse particle (N772) and a medium-high structured coarse particle (N660). For these systems, the rheology and the dispersion colour properties have been investigated. Finally, a rheology study on the effect of bimodal dispersions was undertaken.

Wood plastic composite (WPC) is a material composed of a thermoplastic matrix filled with wood fibers at different concentrations. This material is widely used for decking and automotive applications. With respect to wood it requires less maintenance, shows better durability in wet environment and can be obtained from recycled materials. With respects to plastics the main advantage is its lower cost. The aim of this thesis has been to investigate the mechanical and rheological properties of PP based Wood Polymer Composites. The mechanical characterization has shown that wood fibers make the composite stiffer without lowering strength values too much, while thermal properties have confirmed that the processing window for this material is rather narrow, being limited upwards by wood fiber degradation and downwards by the melting temperature, which is around 165°C. Commercial PP-based WPCs filled with different filler concentration have been investigated with an off – line rheometer in oscillation mode at 170°C. Complex viscosity increases with the percentage of fibers. All materials show a shear-thinning behaviour with similar slopes of the flow curves and neat PP also displays a Newtonian plateau at low shear rates. The test temperature is imposed by the requirement of performing the test within the linear viscoelasticity region, but the data that are measured are not directly useful for processing, as a convenient processing temperature should be around 195°C. In order to obtain the WPC viscosity at such temperatures, a model that uses the WPC viscosity measured at 170°C at various wood quantities and of neat PP viscosity measured at various temperatures is proposed. The main hypothesis of this model is that the effects of temperature and filler content on the composite viscosity are disjoint. These measurements permit to create shift factors that allow to estimate the WPC viscosity on the basis of neat PP viscosity, temperature and fibers content. In order to validate the model, flow curve of 30%wt. and 70%wt. WPC at 195°C have been measured with an instrumented extruder slit die that allows the determination of the flow characteristics of the material in a condition that is very similar to the actual processing conditions. The slit die, connected with a single screw extruder, has a channel that is 50 mm wide and 105 mm long. Three heights are used for the Mooney procedure and three pressure transducers are flush mounted along the slit to eliminate the need for the Bagley correction. The results show that the viscosity curve for the 30% wt. WPC validates the model presented with a reasonably good agreement. Since the agreement for the 70% wt. is less justified and such a material displays a marked yield stress, we can conclude that it is the yield stress that is probably the single issue that makes the present model questionable. In this regard, a future work that we propose is to modify the model by selecting a Carreau-Yasuda model with an yield stress to account for the increase in the viscosity at low shear rates

Une étude combinant expériences et analyses est menée afin de rationaliser la dynamique et la rhéologie des suspensions très concentrées de fibres rigides, non colloïdales dans un fluide newtonien. Des mesures rhéologiques couplées à des mesures de la microstructure sont réalisées à l’aide de plusieurs dispositifs expérimentaux permettant d’analyser différents types de géométries et d’écoulements. Des expériences de rhéologie standards (rhéologie à volume contrôlé), ainsi qu’une méthode de rhéologie non-conventionnelle (rhéologie à pression contrôlée) sont associées afin de mesurer la contrainte de cisaillement, la pression de la phase particulaire et la fraction volumique des suspensions très concentrées. Un autre dispositif expérimental a été conçu dans le but d’étudier la microstructure (distribution spatiale et distribution d’orientations) d’une suspension de fibres rigides dans un écoulement de Poiseuille oscillant. Alors que ce type d’écoulement est réversible pour un liquide newtonien, dans le cas d’une suspension concentrée, les interactions entre particules introduisent des changements irréversibles de microstructure. Cette microstructure est affectée et a un effet sur l’écoulement imposé, cette dépendance non-linéaire incluant les interactions hydrodynamiques. L’objectif de ces expériences est d’apporter un éclairage sur des effets tels que la rhéofluidification observée à fort taux de cisaillement et sur le démixage dû à la migration induite par cisaillement
A combined work of experiments and data analyses is proposed to investigate the dynamics and rheology of highly concentrated suspensions of non-colloidal rigid rods in a Newtonian fluid. Detailed measurements of the rheology and the microstructure are made using a variety of experimental devices with different geometries and imposed flows. Standard rheology experiments (volume-controlled rheology), as well as a novel method of rheometry, are carried out to measure torques, particle pressures, and volume fractions at high concentration (pressure-controlled rheology). Another experiment has been designed and constructed to study the microstructure (spatial and orientation distribution) of a suspension of rigid rods in an oscillatory parabolic flow. Though the flow is reversible in these systems, the changes in the microstructure are irreversibile in the case of concentrated suspensions due to particle interactions. The microstructure is affected by, and has an effect, on the imposed flows; this non-linear dependency includes hydrodynamic interactions. The purpose of these experiments is to gain insight into phenomena such as apparent shear-thinning at high shear rates and demixing due to shear-induced migration

Thesis (Honors)--Ohio State University, 2005.
Title from first page of PDF file. Document formattted into pages: contains vii, 81 p.; also includes graphics. Includes bibliographical references (p. 81). Available online via Ohio State University's Knowledge Bank.

We investigate the behaviour of DNA-colloid systems using micro-rheology, with a view to demonstrating the efficacy of passive particle-tracking methodologies and developing entirely new systems. Chapter 1 introduces the fields of DNA coated colloids (DNACCs) and passive micro-rheology, with a particular fo cus on the challenges of creating an equilibrating DNACC system and the practicalities and limitations of passive microrheology in gaining access to valid rheological information. In Chapter 2, we present a newly developed realtime monitoring algorithm for complex moduli in optical tweezer micro-rheology sys,tems. Further to eliminating high frequency artefacts, our method is memory light and computationally efficient. Chapter 3 investigates the dynamics of ADNA coated colloids using Brownian Dynamics simulation and a theoretical model, also applying the algorithm developed in Chapter 2. A two-regime diffusivity is identified, in contrast to previous works, which simply found an increased hydrodynamic size. Chapter 4 looks at tuning the hydrophobicity of silica particles using poly(L)lysinepolyethylene glycol (PLL-PEG). We find an incubation pH dependence on their coverage. From analysing video microscopy trajectories, PLL-PEG coated beads sedimented onto A-DNA brushes are found to be significantly more diffusive. In Chapter 5, we int roduce an entirely new DNACC system, the functionalised fd bacteriophage, where high aspect ratio filamentous virions are coated with short oligonucleotides. Aggregation behaviour is confirmed with Atomic Force Microscopy and Dynamic Light Scattering, and systems where rods can act as a linker between spherical particles are also briefly investigated.

A brief review is made of the rheology of suspensions in general and cement slurries in particular. The factors influencing the flow behaviour of these systems are discussed. It is pointed out that the rheological properties of cement slurries can not be determined by theory alone from the original constituents, and experimental tests combined with empirical formulae are needed. The co-axial cylinder viscometer was used to characterise the rheological behaviour of the cement slurry used in this investigation, the slurry being made highly thixotropic by the use of additives, It is shown that no single flow model, however complex, can correctly fully describe the flow behaviour of such materials. The cement slurry used in this research programme had a structure which changed continuously with time and, when pumped through a pipe, formed a high water content slip layer on the pipe surface. An accurate theoretical solution for this type of pipe flow is lacking in the literature. A new method to predict the pressure gradient of such suspensions flowing in pipes is proposed and the technique was tested using a small pumping line and also with data extracted from the literature. The shear vane test, commonly used to measure shear strength of soils, was developed to measure gel strength of the cement slurry used in this investigation. It is shown that the gel strength measured with this technique is of considerable benefit when assessing the real material behaviour.

Abstract In order to improve the optimisation of mineral processing operations the rheological properties of slurries must be determined as accurately as possible under the conditions that closely resemble actual site conditions. The rheology of particles suspended in Newtonian fluids is well documented. However, the rheology of particles in non-Newtonian fluids has not been the subject of much investigation till now. The work conducted here attempts to fill this gap in knowledge. The rheological properties of slurries are heavily dependent on the solids concentrations and particle-solid interaction. At low solids concentrations, constant viscosity and Newtonian behaviour is observed, but as solids concentration increases the rheological behaviour becomes increasingly complex and non-Newtonian with viscosity becoming dependent on the shear rate. The nature of the non-Newtonian behaviour depends on the solid concentration, particle shape, particle size, particle size distribution and the suspending liquid rheological properties. The suspension/slurry may develop a yield stress and become time dependent in nature as structures develop within the fluid at higher solids concentrations. This study however, is primarily focused on the measurement of the rheological properties, where it is assumed that the fluid will be fully sheared and that the rheological properties will be unlikely to change with time. Shear thickening behaviour of slurries was the focus of this work. The aim was to investigate the slurry concentration region where shear thickening occurs. The first objective of the project was to develop a fluid analogue which will have similar rheological behaviour to that of concentrated tailings from gold mines so that it can be used as a test material to simulate the flow behaviour of the tailings in a pipe. The second objective of this project was to enable the prediction of flow behaviour in the pipe loop under certain conditions using the fluid analogue for slurry from Sunrise dam. In order to achieve the objectives, experiments were carried out to obtain a fluid analogue of a shear thickening slurry. CSL 500 and SR 200 rheometers were used for the characterisation of different fluid analogues and shear thickening mineral slurries. Malvern Sizer, model: mastersizerX v1.1, was used to obtain particle size distributions. A mini pipe loop system, located in the laboratory of the Rheology and Materials Processing Centre (RMPC) was used to get pipe line flow data for comparison with the rheometer data. A few fluid analogues with different suspending medium and different concentrations of glass spheres was tested before finally using, 48 vol% glass spheres in 1.8 wt% CMC solution as a fluid analogue for the mineral tailings obtained from Sunrise dam, WA. For comparison between the pipe line and rheometer data, all pipe line data (in the form of 8V/D) were converted to rheometer data (in the form of du/dr) using the Robinowitsch-Mooney equation. The above comparison indicated that it is possible to produce fluid analogue to simulate the flow behaviour of Sunrise dam slurry using a shear thinning suspending medium with high concentration of glass particles. Shear thickening flow behaviour was clearly observed in the rheometer while it was less predominant in a pipe line flow.

Taken as an engineering material, mozzarella cheese can be considered as a complex food system that has dynamic structure and complex flowproperties. Food scientists have been actively developing methods to characterize mozzarella cheese rheologically, but most of these methods are empirical in nature. In the past decades, there has been a paradigm shift towards the utilization of well-developed rheological methods which have been widely applied in the study of commercial synthetic polymers. In this work, the rheology of mozzarella cheese was studied using well-developed rheological techniques. Utilizing various rheometers, the linear and non-linear rheology of mozzarella cheese was examined. General practical properties of mozzarella cheese such as meltability, flowability and stretchability were extracted from these results. Capillary flow and rolling experiments were also performed to determine their suitability as innovative post-production processing techniques for mozzarella cheese. Finally, a comparative study on the effect of frozen storage on the rheology of three different brands of mozzarella cheese was performed. In general, it was found that mozzarella cheese can be classified as a pseudoplastic (shear thinning) semi-solid material possessing a yield stress at room temperature. Upon heating, the yield stress gradually diminishes and it can be considered as a viscoelastic fluid. The results obtained from the various rheometers indicate that the yield stress, duration of experiment, sample geometry and temperature greatly affect the consistency of the results. It was also shown that extrusion can be used as a processing technique for mozzarella cheese above a certain temperature where the cheese is in a melt state. Rolling was also found to be a potentially feasible processing method. Finally, in terms of the effect of frozen storage, in general, the dynamic moduli decrease with the period of storage due to the freezing of the proteins in the cheese.

A series of linear and H-shaped polybutadienes (PBDs) were prepared by living anionic polymerization. These polymers were prepared in a novel way using a DPE derivative instead of a difunctional initiator to prepare the cross-bar. This new synthesis strategy was designed to reduce the presence of intermediate species and undesired by-products in the final samples. Details of the structures were revealed using temperature gradient interaction chromatography (TGIC) and the results were compared with those indicated by size exclusion chromatography (SEC) data from reputable researchers at three laboratories. Discrepancies in molecular weights and molecular weight distributions were observed amongst the three sets of SEC data. Furthermore, TGIC, which is believed to have a higher resolution than SEC, revealed that the H-shaped PBDs were actually mixtures of components having several molecular structures. Rheological characterizations were carried out over a broad frequency range by combining small amplitude oscillatory shear (SAOS) and creep (and recovery in some cases) data. Time-temperature superposition was found to work well at temperatures ranging from -75oC to 25oC, and dynamic moduli inferred from creep (or creep/recovery) data agreed well with the SAOS data at the reference temperature Tref=25oC. Material constants including the zero shear viscosity , plateau modulus and steady state compliance were extracted from experimental data. The effects of long-chain branching and polydispersity of arms and cross-bars on rheological behavior were studied. Two tube-based models: The Hierarchical-3.0 model developed by Larson et al. and the branch-on-branch (BoB) model of Das et al. were evaluated and compared quantitatively. The evaluation consisted of a summary of peer reviews, sensitivity and uncertainty analyses and comparison of simulations with experimental data. Hierarchical-3.0 gave the most accurate predictions for the H-shaped polymers when polydispersity in t
Des polybutadiènes linéaires et à structure branchée en « H » (avec deux points de branchement) ont été synthétisés par polymérisation anionique en utilisant un dérivé du diphényle-éthylène à la place d'un amorceur bi-fonctionnel pour synthétiser le segment connectant les deux points de branchement. Cette nouvelle approche a permis de réduire le nombre de produits intermédiaires et de structure moléculaires indésirables dans les échantillons produits. Une comparaison de la structure moléculaire déterminée par une méthode chromatographique à gradient de température (TGIC) avec les résultats de trois études indépendantes par chromatographie d'exclusion (SEC) réalisées par des experts en la matière a révélé des différences, en particulier parmi les résultats de SEC. La méthode TGIC, jugée plus précise et sensible, a établi que les échantillons de polybutadiène « H » étaient un mélange de structures diverses. Le comportement rhéologique sur une large gamme de fréquences a été déterminé en combinant des données dynamiques à faible amplitudes avec des donnés de fluage. Le principe de superposition temps-température a été validé entre -75°C et 25°C, et le module complexe déduit des données de fluage-recouvrance est en bon accord avec le module directement mesuré dans le mode oscillatoire à la température de référence (25°C), ce qui a permis la détermination de la viscosité au plateau Newtonien, du module et de la complaisance à l'équilibre. L'influence de la présence de longues branches et de la polydispersité des branches et du segment entre les points de branchement a été étudiée, et les données rhéologiques ont été utilisées pour évaluer deux modèles théoriques basés sur la théorie de la reptation. Le modèle hiérarchique « Hierarchical-3.0 » développé par Larson et al., et le modèle BoB (« branch-on-branch ») proposé par Das et al. ont été comparés sur la base d

We develop a mesoscopic theoretical framework to study viscoelastic response of block copolymers in the vicinity of their order-disorder transition point. We use it to study orientation selection of lamellar phases of diblock copolymers under oscillatory shears. We examine the effect of hydrodynamics on the relaxation of lamellar phases, and include anisotropic viscous stresses that follow from the uniaxial nature of the phase. We also introduce network viscoelastic effects that model chain entanglements, also made consistent with the symmetry of the phase. A numerical algorithm has been developed to solve the governing equations, which has been implemented on a parallel computer architecture. Simple cases involving the relaxation of small transverse perturbations, or viscoelasticity arising from diffusive relaxation of the order parameter have been investigated, and used to validate the numerical code. We also address the issue of spontaneous orientation selection from an initially disordered state due to an imposed oscillatory shear. In the absence of hydrodynamic coupling, we observe that the so called parallel orientation is selected for small shear frequency and amplitude, crossing over to a perpendicular orientation at higher shear frequencies and amplitudes. Hydrodynamic effects are seen to shift this crossover region. We have also examined the effect of network entanglement at finite frequencies. We find that network entanglement can lead to faster alignment, and that anisotropic network stresses can significantly influence the orientation selection process.
Nous developpons un cadre theorique propre a l'echelle me oscopique dans le but d'etudier la reponse viscoelastique des blocs de copolymeres pres du point de transition entre leur etat ordonne et desordonne. Nous utilisons cette theorie pour e tudier la selection de l'orientation des phases de lamelles des blocs de copolymeres subissant des cisaillements oscillatoires. Nous examinons les effets hydrodynamiques de la relaxation des phases lamellaires et nous incluons les stress visqueux anisotropes, dues a la nature uniaxiale des phases. Nous introduisons aussi les effets viscoelastique relatifs aux r eseaux modelisant l'enchevetrement des chaines dans une approche consistante avec la symetrie des phases. Un algorithme nume rique sous implementation parallele a ete developpe pour resoudre les equations relatives a cette etude. Des cas simples impliquant la relaxation diffuse du parametre relatif a l'ordre ont ete examines et utilises pour verifier le code numerique. Nous adressons aussi la question de la selection de l'orientation spontane d'un etat initialement desordonne due a un cisaillement oscillatoire impose au systeme. Dans l'absence d'interaction hydrodynamique, nous observons que l'orientation denomme e parallele est selectionnee pour des petites frequences et amplitudes de cisaillement mais adopte une orientation perpendiculaire pour de grandes frequences et amplitudes de cisaillement. Les effets hydrodynamiques changent la region de transition. Nous avons aussi examin e l'effet d'enchevetrement du reseau pour des frequences finies. Nous trouvons que l'enchevetrement du reseau mene a un alignement plus rapide et que les stress des reseaux anisotropes peuvent influencer de maniere significative le processus de se lection d'orientation.

This thesis presents the results of laboratory experiments, theoretical analysis, field work and petrological analysis conducted to study the rheology and dynamics of lava flows. The rheology of suspensions of cubic crystals in viscous liquids was investigated with a series of experiments, consisting of the release of a fixed volume of fluid inside a horizontal channel. A Herschel-Bulkley rheology was assumed and the consistency K and the shear rate exponent n of this constitutive equation were calculated using the evolution of the flow front; the yield strength was calculated using the final shape of the flow. Results show an increase in K when crystal content increases. The mixtures start to show a shear thinning behaviour at 4>-0.3 with n values going from approximately 1 (Newtonian behaviour) to 0.5 at 4>=0.6. Yield strength was detected at the same 4> as the beginning of shear thinning behaviour and increases with a power-law relationship with crystal content. Suspensions with bimodal crystal sizes show a dramatic decrease of the apparent viscosity compared to unimodal suspensions, especially at the higher total crystal concentrations. Further experiments, with the same types of fluids (with approximately Herschel- Bulkley rheology) in a sloping channel with a constant flux rate were approximated with a simplified 2-D model. The results show an excellent agreement between the theory and the experiments. Additionally, experiments with two fluids, where a low viscosity fluid (syrup) is injected in a fixed volume of more viscous material (syrup plus crystals) suggest that the front advance and height is controlled mainly by the rheology of the fixed volume fluid. The simplified 2-D theory was applied to real lava flows. Three dynamical regimes were considered: A Newtonian viscous regime, a yield strength-dominated regime, and a crust-dominated regime. The resulting equations were applied to published data from eruptions of 10 lava flows with a range of compositions and conditions. Comparisons of the fits of the models to the data reveal that short-lived, high effusion rate eruptions typical of Hawaiian lava flows, are dominated by the internal viscosity of the lava, whereas low effusion rate or long lived eruptions are dominated by the yield strength in the growing crust. Finally, eruptions with very high initial crystal contents are dominated by the internal yield strength. The developed rheological model and 2-D theory were applied to the 2002 lava flow deposits at the NE flank of Etna volcano to reconstruct the variations in flow rate and advance of the flow front. Analyses of samples were used to estimate crystal content and liquid viscosity variations with distance. Yield strength variations were estimated from levee width measurements. The modelled flow rate and advance of the flow front compare well with the measured data, with a mean flow rate of 19.5 m3/s. The method developed in this thesis provides the prospect of using measurements of flow dimensions together with analysis of samples from the deposits to estimate the rheology of the flow and reconstruct variations of eruption parameters.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references (leaves 24-25).
We present a novel optical methodology including both instrumentation and theory aimed at retrieving the full viscoelastic information of cell membrane material properties. Red blood cells (RBC) are chosen for this study because of their simple structure, which consists of a bi-layer cell membrane supported by a cytoskeleton enclosing a homogeneous fluid. The full complex modulus of RBC in terms of temporal frequency and spatial frequency is retrieved 'without contact, for the first time to our knowledge. Sub-nanometer sensitivity diffraction phase and fluorescence microscopy (DPF) quantifies non-invasively three dimensional morphological information of live cell with high speed. The fluctuation dissipation theory and generalized Stokes-Einstein relationship provide the complex modulus associated with the cell membrane, in a spatially-resolved manner. This information is used to retrieve the dynamic and spatial behavior of red blood cell membranes during the process of shape deterioration. The viscoelasticity results on RBC strongly correlate with cell morphology. Thus, we find that the cell evolution from a normal, doughnut shape to a spheroid can be interpreted from a viscoelastic point of view as a liquid-solid transition.
by YongKeun Park.
S.M.

Foams are ubiquitous in many industrial processes and therefore have been subjected to extensive research in the past few decades. However, a number of fundamental issues relating to foams remain poorly understood including the production and control of bubbles and how they contribute to product structure, appearance, and rheology. The work in this thesis thus sets out to study the foam rheological behaviour and its related structural evolution, to explore a potential method in controlling bubble structure during foam generation, and to introduce a novel non-invasive technique in probing foam microstructure. Foam rheological behaviour was studied by using two approaches. In a rheometric approach, the foam response to external shear and the related microstructural change, its time dependency, thixotropic behaviour and viscoelastic properties were investigated for both detergent (Gillette) and protein (egg white protein) foams. The flow curves constructed were well fitted with four-parameter rheological models, the Cross and Carreau models and revealed the true flow behaviour of foam; there was no yield stress as reported in the literature. On the other hand, the macroscopic flow behaviour of a protein foam (WPC) in straight pipes and through fittings (sudden expansion, orifice plates and perforated plates) were studied. A friction factor analysis approach which treats foam as a non-Newtonian power law fluid was successfully used to model the flow of WPC foam, this has a practical significance in that pressure drop can be calculated using a constant friction factor along a pipe of a constant cross section in any flow regime. The potential of ultrasound in controlling foam structure during the foam generation process was investigated. Depending on the types of surfactant and concentrations, ultrasound reduced the mean bubble size of foams and improved foam homogeneity. Single bubble formation in an ultrasound field managed to shed light onto the possible mechanism involved; ultrasound increased the bubble formation rate and reduced the bubble coalesce events at the nozzle. X-ray micro-computed tomography was used successfully in revealing the true three dimensional structure of some cellular/foam food products, both solid and semi liquid. Both two- and three-dimensional quantitative analyses of structural parameters were done and the spatial bubble size distribution was reconstructed using a stereology technique.