The transient extensional rheology and the dynamics of elastocapillary thinning in aqueous solutions of polyethylene oxide (PEO) are studied with high-speed digital video microscopy. At long times, the evolution of the thread radius deviates from self-similar exponential decay and competition between elastic, capillary and inertial forces leads to the formation of a periodic array of beads connected by axially-uniform ligaments. This configuration is unstable and successive instabilities propagate from the necks connecting the beads and ligaments. This iterated process results in multiple generations of beads developing along the string in general agreement with predictions of Chang et al. [Phys Fluids, 11, 1717 (1999)] although the experiments yield a different recursion relation between the successive generations of beads. At long times, finite extensibility truncates the iterated instability, and slow axial translation of the bead arrays along the interconnecting threads leads to progressive coalescence before the ultimate rupture of the fluid column. Despite these dynamical complexities it is still possible to measure the steady growth in the transient extensional viscosity by monitoring the slow capillarydriven thinning in the cylindrical ligaments between beads. / Accepted for publication in JNNFM, December 2005. / NASA and the Portuguese Science Foundation

In separating the Form from its particulars, Plato is left with the task of describing the way in which they are related to one another. One possible way of construing this relation is to suppose that particulars receive a share ofthe Form. The discussion between Parmenides and Socrates, in the Parmenides 131 a9-e3, interprets this sharing in a material sense: either the whole of the Form is received by each particular, or part of the Form is received by each particular. This disjunction turns out to be a destructive dilemma -the socalled Dilemma of Participation. The three main sections ofthis work study in detail the Dilemma of Participation, as it is presented in the Parmenides. The first section considers the disjunct that the whole of the Form is received by each particular (13 la9-b2). By using a system of classical extensional mereology, it is demonstrated that Parmenides' reductio ad absurdum of this disjunct is deductively valid. The second section deals with Socrates' objection to this argument (which he makes in the guise of the Day Analogy), and Parmenides' response to the objection (which he makes in the guise ofthe Sail Analogy) (131 b3-c4). The validity of Parmenides' response depends on the sense of"day" Socrates intends in the Day Analogy. It is argued (against S. Panagiotou) that there is a sense of "day" that makes Parmenides' response invalid. The third section considers the disjunct that part of the Form is received by each particular (131 c5-e3). Two current interpretations of this disjunct (that ofT. Scaltsas and R. E. Allen) are recounted and critiqued, and a new interpretation is proposed (an interpretation based partially on that of Proclus, and under which Parmenides' argument against this disjunct is valid). / Thesis / Master of Arts (MA)

no / The shear and extensional properties of injection moulding grade hydroxyapatite¿polyethylene composites developed for orthopaedic applications have been studied. The composite was prepared without processing aids owing to concerns over the potential biological responses to such additives. The composite containing 20 vol.-% hydroxyapatite filler showed typical pseudoplastic behaviour. However, that containing 40 vol.-% hydroxyapatite filler tended to exhibit yield. The Maron¿Pierce equation was found to be useful in predicting the viscosities of the composite systems. The activation energy of the composite and the unfilled polymer were equal, indicating that the 20 vol.-% system exhibits the same flow mechanism as the unfilled polymer. A qualitative assessment of extensional properties was made following Cogswell's method. The extensional stress of the unfilled polymer decreases with increasing temperature whereas the composites behave in a complex manner. For all the systems the Trouton ratios tend to increase with apparent shear rates. The Trouton ratio also indicates that at higher temperatures the flow of these composites is dominated by extensional properties.

The design of fiber-reinforced thermoplastic (FRT) parts is hindered by the determination of the various empirical parameters associated with the fiber orientation models. A method for obtaining these parameters independent of processing doesn't exist. The work presented here continues efforts to develop a rheological test that can obtain robust orientation model parameters, either by fitting directly to orientation data or by fitting to stress-growth data. First, orientation evolution in a 10 wt% long-glass-fiber-reinforced polypropylene during two homogeneous flows (startup of shear and planar extension) was compared. This comparison had not been performed in the literature previously, and revealed that fiber orientation is significantly faster during planar extension. This contradicts a long-held assumption in the field that orientation dynamics were independent of the type of flow. In other words, shear and extension were assumed to have equal influence on the orientation dynamics. A non-lubricated squeeze flow test was subsequently implemented on 30 wt% short-glass-fiber-reinforced polypropylene. An analytical solution was developed for the Newtonian case along the lateral centerline of the sample to demonstrate that the flow is indeed a superposition of shear and extension. Furthermore, an existing fiber orientation model was fit to the gap-wise orientation profile, demonstrating that NLSF can, in principle, be used to obtain fiber orientation model parameters. Finally, model parameters obtained for the same FRT by fitting to orientation data from startup of steady shear are shown to be inadequate in predicting the gap-wise orientation profile from NLSF. This work is rounded out with a comparison of the fiber orientation dynamics during startup of shear and non-lubricated squeeze flow using a long-fiber-reinforced polypropylene. Three fiber concentrations (30, 40, and 50 wt%) were used to gauge the influence of fiber concentration on the orientation dynamics. The results suggest that the initial fiber orientation state (initially perpendicular to the flow direction and in the plane parallel to the sample thickness) and the fiber concentration interact to slow down the fiber orientation dynamics during startup of shear when compared to the dynamics starting from a planar random initial state, particularly for the 40 and 50 wt% samples. However, the orientation dynamics during non-lubricated squeeze flow for the same material and initial orientation state were not influenced by fiber concentration. Existing orientation models do not account for the initial-state-dependence and concentration-dependence in a rigorous way. Instead, different fitting parameters must be used for different initial states and concentrations, which suggests that the orientation models do not accurately capture the underlying physics of fiber orientation in FRTs. / Ph. D. / In order to keep pace with government fuel economy legislation, the automotive and aerospace industries have adopted a strategy they call “lightweighting”. This refers to decreasing the overall weight of a car, truck, or plane by replacing dense materials with less-dense substitutes. For example, a steel engine bracket in a car could be replaced with a high-temperature plastic reinforced with carbon fiber. This composite material will be lighter in weight than the comparable steel component, but maintains its structural integrity. Thermoplastics reinforced with some kind of fiber, typically carbon or glass, have proven to be extremely useful in meeting the demands of lightweighting. Thermoplastics are materials that can be melted from a feedstock (typically pellets), reshaped in the melted state through use of a mold, and then cooled to a solid state, and some common commodity-grade thermoplastics include polypropylene (used for Ziploc bags) and polyamides (commonly called Nylon and used in clothing). Although these commodity applications are not known for their strength, the fiber reinforcement in the automotive applications significantly improves the structural integrity of the thermoplastics. The ability to melt and reshape thermoplastics make them incredibly useful for highthroughput processes such as injection molding. Injection molding takes the pellets and conveys them through a heated barrel using a rotating screw. The melted thermoplastic gathers at the tip of the barrel, and when a set volume is gathered, the screw is rammed forward to inject the thermoplastic into a closed mold of the desired shape. This process typically takes between 30-60 seconds per injection. This rate of production is crucial for the automotive industry, as manufacturers need to put out thousands of parts in a short period of time. The improvement to mechanical properties of the thermoplastics is strongly influenced by the orientation of the reinforcing fibers. Although design equations connecting the part’s mechanical properties to the orientation of the fibers do exist, they require knowledge of the orientation of the fibers throughout the part. Fibers in injection-molded parts have an extremely complicated orientation v state. Measuring the orientation state at each point would be too laborious, so empirical models tying the flow of the thermoplastic through the mold to the evolving orientation state of the fibers have been developed to predict the orientation state in the final part. These predictions can be used in lieu of direct measurements in the part design equations. However, the orientation models rely on empirical fitting parameters which must be obtained before injection molding simulations are performed. There is currently no standard test for obtaining these parameters, nor is there a standardized look-up table. The work presented in this dissertation continues efforts to establish such a test using simple flows in a laboratory setting, independent of injection molding. Previous work focused exclusively on using shearing flow (e.g. pressure-driven flow found in injection molding) to obtain these parameters. However, when these parameters were used in simulations of injection molding, the agreement between measured and predicted fiber orientation was mediocre. The work here demonstrates that another type of flow, namely extensional flow, must also be considered, as it has a non-negligible influence on fiber orientation. this is crucial to injection molding, as injection molding flows have elements of both shearing and extensional flow. The first major contribution from this dissertation demonstrates that extensional flow (e.g. stretching a film) has a much stronger influence than shearing flow, even at the same overall rate of deformation. The second major contribution used a combination shear/extensional flow to demonstrate that the empirical model parameters, thought to be characteristic of the composite, are actually strongly influenced by the type of flow experienced by the sample, and that no single set of model parameters can fit the full orientation state. The final major contribution extends the previous case to long-fiber reinforcement at multiple fiber concentrations which are of industrial interest. This finds the same results, that the model parameters are dependent on the type of flow experienced by the sample. The flow-dependence of the parameters is a crucial point to address in future work, as the flows found in injection molding contain both shearing and extensional flow. By further developing this flow-type dependence, future injection molding simulations should become more accurate, and this will make computer-aided injection-molded part design much more efficient.

[pt] Neste trabalho foi analisado o escoamento de fluidos não Newtonianos através de canais axisimétricos convergentes divergentes. A solução da conservação de massa e de conservação de momento foi obtida numericamente via volumes finitos utilizando o programa de computador Fluent. A equação constitutiva de fluidos Newtonianos generalizados foi utilizada para modelar o comportamento não Newtoniano, utilizando a equação constitucional de Shunk-Scriven para cálculo da viscosidade, que assume como sendo a média geométrica ponderada pelo classificador de escoamento R entre a viscosidade de cisalhamento e a viscosidade de extensão. Os resultados de perda de pressão e vazão são comparados com os resultados calculados pela relação simplificada proposta por Souza Mendes e Naccache, 2002 entre a perda de carga e vazão de fluidos viscoelásticos fluindo através do meio poroso, para analisar a sua performance. / [en] In this work, the flow of non-Newtonian fluids through axisimmetric convergingdiverging channels is analyzed. The solution of mass and momentum conservation equations is obtained numerically via finite volume technique using the Fluent software. The Generalized Newtonian Fluid constitutive equation was used to model the non- Newtonian fluid behavior, using the Shunk-Scriven model for the viscosity, where a weighted geometric mean by the flow classifier R between shear and extensional viscosities is assumed. The results of pressure drop and flow rate are compared to the ones predicted by a previously proposed simplified relation (Souza Mendes and Naccache, 2002) between pressure drop and flow rate, for viscoelastic fluids flow through porous media, in order to analyze its performance.

[pt] A poliacrilamida parcialmente hidrolisada (HPAM) é amplamente empregada no processo de recuperação avançada de petróleo (EOR). No entanto, sua eficácia é prejudicada pela degradação das moléculas do polímero durante o fluxo através das linhas de injeção, válvulas e reservatório. Essa degradação leva a uma diminuição do peso molecular médio e, consequentemente, reduza viscosidade e as propriedades viscoelásticas da solução, afetando sua eficácia no deslocamento do petróleo. Para abordar essas questões, nossa pesquisa caracterizou o grau de degradação mecânica das soluções de HPAM usando reologia de cisalhamento e extensional. Induzimos a degradação fazendo as soluções fluírem por uma válvula com constrição e diferentes vazões através deum modelo microfluídico de um médio poroso. Os resultados revelam que aadição de nanopartículas de sílica (SiO2) tem um efeito insignificante sobreas viscosidades de cisalhamento e extensional de soluções frescas e minimiza a degradação mecânica das soluções de HPAM. As propriedades reológicas das soluções de HPAM com nanopartículas de SiO2 não são significativamente afetadas pela degradação mecânica, o que sugere que a incorporação de nanopartículas poderia aumentar a eficiência da injeção de polímeros em processosde EOR por meio da estabilização das soluções de HPAM. Além disso, nosso estudo explorou escoamento de deslocamento de óleo usando soluções de polímero HPAM frescas e degradadas em dispositivos microfluídicos usados como modelos de meios porosos. Os resultados sugerem que o HPAM fresco é mais eficiente na produção de óleo do que o HPAM degradado. Além disso, a adição de nanopartículas de sílica em soluções degradadas de NPs-HPAM resultou em um aumento de 9-13 por cento na recuperação de petróleo, destacando o enorme potencial das nanopartículas no aprimoramento dos processos de EOR. / [en] Partially hydrolyzed polyacrylamide (HPAM) is widely employed in enhanced oil recovery (EOR) process. However, its effectiveness is hindered by degradation of polymer molecules during flow through injection lines, valves and reservoir. This degradation leads to a decrease in average molecular weight and subsequently reduces the solution’s viscosity and viscoelastic properties, impacting its effectiveness on displacing oil. Our research characterized the degree of mechanical degradation of HPAM solutions using shear and extensional rheology. We induced degradation by flowing the solutions through a valve with varying constriction and flow rates and through a microfluidic porous medium model. Our findings reveal that the addition of silica (SiO2) nanoparticles has a negligible effect on the shear and extensional viscosities of fresh solutions and minimizes the mechanical degradation of HPAM solutions. The rheological properties of HPAM solutions with SiO2 nanoparticles are not significantly affected by mechanical degradation, suggesting that incorporating nanoparticles could enhance the efficiency of polymer injection in EOR processes by stabilizing HPAM solutions. In addition, our study explored oil displacement flow using both fresh and degraded HPAM polymer solutions in microfluidic devices used as models of porous media. The findings suggest that fresh HPAM is more efficient in displacing oil than degraded HPAM. Furthermore, the addition of silica nanoparticles into degraded NPs-HPAM solutions resulted in a 9-13 percent increase in oil recovery, highlighting the enormous potential of nanoparticles in enhancing EOR processes.

Les structures extensives d'âge Mésozoïque tardif (Crétacé) sont très répandues en Eurasie orientale, depuis la Transbaïkalie en Russie jusqu'à l'intérieur de la Chine du Sud. Elles constituent la plus grande province de distension crustale dans le monde. Cette thèse a sélectionné des structures développées dans trois endroits différents du bloc de Chine du sud en utilisant les méthodes de la géologie structurale, de l'anisotropie de la susceptibilité magnétique et de la géochronologie (U-Pb sur zircon et titanite, U-Th-Pb sur monazite et Ar-Ar sur micas et amphiboles). L'expression des structures extensives diffère selon les endroits étudiés: (1) la ceinture orogénique de HP/UHP Tongbai-Dabie, le long de la bordure nord du bloc de Chine du sud a été remaniée par au Crétacé par la formation d'un antiforme ou d'un dôme métamorphique extensif. Contemporaine de la migmatisation et du magmatisme syntectonique, le régime extensif a commencé à environ 145 Ma et s'est approché de son point culminant vers 130 Ma. Ce qui a été interprété comme le résultat de la suppression de la racine orogénique. Localement, un nouvel épisode de distension vers 110-90 Ma a également été enregistré; (2) le batholite de Dayunshan-Mufushan intrudif dans l'orogène Neoproterozoic Jiangnan se compose de deux phases d'intrusions granitiques d'âge Jurassique (ca. 150 Ma) et Crétacé inférieur (ca. 132 Ma). Le pluton le plus récent s'est mis en place dans un contexte d'extension NW-SE correspondant au processus amincissement crustal du Crétacé inférieur, avec une faille de détachement développée le long de sa bordure ouest; (3) l'anticlinal de Huangling dans le craton du Yangtze est un pli asymétrique d'axe N-S formé entre le Jurassique et le Crétacé inférieur. Sur les deux flancs, la couverture sédimentaire a participé à une série de plis d'effondrement de vergence opposée et de glissements banc-sur-banc des couches. Les exemples étudiés ci-dessus représentent une série de structures d'extension d'âge Crétacé développées dans différents niveaux structuraux: exhumation de croûte inférieure et moyenne de accommodée par un fort étirement, mise en place syntectonique de plutons granitiques avec étirement limité, déformation de la couverture sédimentaire sous une faible extension. Ils indiquent que la Chine du Sud a également participé au régime extensif bien connu en Chine du Nord. Ces résultats apportent des données nouvelles de première main permettant de discuter le cadre tectonique et géodynamiques spatio-temporel du régime extensif du Crétacé sur la marge orientale de l'Eurasie. / Late Mesozoic extensional structures are widespread in eastern Eurasia (from Transbaikalia region in Russia to inland South China). They constitute the largest crustal extensional province in the world. This thesis selected extensional structures developed in three different tectonic settings in the South China block. Detailed studies including structural geology, anisotropy of magnetic susceptibility and geochronology (zircon and titanite U-Pb, monazite U-Th-Pb, and mica Ar-Ar) were conducted. The expression of these extensional structures is not the same for each area: (1) the Tongbai-Dabie HP/UHP orogenic belt along the northern edge of the South China block was reworked by Cretaceous extensional antiform or metamorphic core complex. Coeval with migmatization and syntectonic magmatism, the extensional regime started at ca. 145 Ma, and approached its climax at ca. 130 Ma that was signaled by removal of the orogenic root. Locally, a late (110-90 Ma) extensional event was also recorded; (2) the Dayunshan-Mufushan batholith intruding the Neoproterozoic Jiangnan orogen is composed of two phases of granitic intrusions with Late Jurassic (ca. 150 Ma) and Early Cretaceous (ca. 132 Ma) ages, respectively. The late pluton emplaced under a NW-SE extensional setting corresponding to the Early Cretaceous crustal thinning process, with a detachment fault developed along its western margin; (3) the Huangling anticline within the Yangtze craton is a nearly N-S striking asymmetric dome formed between the Late Jurassic and Early Cretaceous. The sedimentary cover on the two flanks was involved in a series of oppositely-directed collapse folding and layer-parallel slipping. These examples of Cretaceous extensional structures in different tectonic levels (exhumation of middle-lower crust by strong stretching, syn-tectonic emplacement of granitic pluton with limited stretching, deformation of sedimentary cover under a weak extension) indicates that South China also was involved into the regional extensional regime coeval with the destruction of the North China craton. These results provide first-hand new structural evidence for further discussing the temporal-spatial framework and geodynamic setting of the Cretaceous extensional tectonics on the eastern margin of Eurasia.

Grasshopper basin, located in southwest Montana, is an east-tilted graben bounded by the listric Muddy-Grasshopper fault and the Meriwether Lewis fault on the eastern and western margins of the basin, respectively. This basin contains a complex stratigraphy of intertonguing facies comprised of five unconformity-bounded sequences of Tertiary alluvial, flu vial, deltaic, and lacustrine sedimentary and volcanic rocks. Sequence 1 consists of the Challis volcanic Group (Middle Eocene). The sedimentary rocks of the Medicine Lodge beds (Late Eocene-Late Oligocene) represent sequence 2 and approximately 90% of the basin-fill within Grasshopper basin. Sequence 3 consists 11 of the Sedimentary Rocks of Everson Creek (Late Oligocene-Early Miocene), sequence 4 is represented by the Sedimentary Rocks of Bannack Pass (Middle-Late Miocene), and the Six Mile Creek Formation (Late Miocene?) corresponds to sequence 5. Sequence 2 is the synrift deposit for the Muddy-Grasshopper fault, and was dominated by lakes that filled axially by rivers from the north. Transverse sediment influx was present on small fan-delta complexes shed into the lake from the eastern margin and periodic large fluvial-dominated alluvial fan and deltaic deposition from the western margin. Paleocurrent analyses are consistent with these observations and show predominantly south-southeastward axial paleoflow directions with west-directed and east-directed paleoflow on the eastern and western margins, respectively. Petrologic studies, including sandstone petrography and conglomerate petrology, reveal a mixed "basement uplift" and "recycled orogen" tectonic provenance. These findings support a model for Eocene-Oligocene rifting characterized by moderate to high relief superimposed on the Cretaceous-Early Tertiary Sevier fold-and-thrust belt. Paleogeographic reconstructions of Grasshopper basin reveal the lack of a southern basin margin. A correlation of the basin-fill contained in the Medicine Lodge and Horse Prairie basins to the south with the Medicine Lodge beds (sequence 2) in Grasshopper basin suggests that each of these basins represents a third of a larger preexisting extensional basin that was partially dismembered by later phases of continued extension. Large extensional folds in Grasshopper basin had a small influence on facies architecture in the basin.

Traditional blowing agents (e.g., hydrochlorofluorocarbons) in plastic foaming processes has been phasing out due to environmental regulations. Plastic foaming industry is forced to employ greener alternatives (e.g., carbon dioxide, nitrogen), but their foaming processes are technologically challenging. Moreover, to improve the competitiveness of the foaming industry, it is imperative to develop a new generation of value-added plastic foams with cell structures that can be tailored to different applications. In this context, the objective of this thesis is to achieve a thorough understanding on cell nucleation and growth phenomena that determine cell structures in plastic foaming processes. The core research strategy is to develop innovative visualization systems to capture and study these phenomena. A system with accurate heating and cooling control has been developed to observe and study crystallization-induced foaming behaviors of polymers under static conditions. The cell nucleation and initial growth behavior of polymers blown with different blowing agents (nitrogen, argon and helium, and carbon dioxide-nitrogen mixtures) have also been investigated in great detail. Furthermore, two innovative systems have been developed to simulate the dynamic conditions in industrial foaming processes: one system captures a foaming process under an easily adjustable and uniform extensional strain in a high temperature and pressure environment, while the other achieves the same target, but with shear strain. Using these systems, the extensional and shear effects on bubble nucleation and initial growth processes has been investigated independently in an isolated manner, which has never been achieved previously. The effectiveness of cell nucleating agents has also been evaluated under dynamic conditions, which have led to the identification of new foaming mechanisms based on polymer-chain alignment and generation of microvoids under stress. Knowledge generated from these researches and the wide range of future studies made possible by the visualization systems will be valuable to the development of innovative plastic foaming technologies and foams.

Traditional blowing agents (e.g., hydrochlorofluorocarbons) in plastic foaming processes has been phasing out due to environmental regulations. Plastic foaming industry is forced to employ greener alternatives (e.g., carbon dioxide, nitrogen), but their foaming processes are technologically challenging. Moreover, to improve the competitiveness of the foaming industry, it is imperative to develop a new generation of value-added plastic foams with cell structures that can be tailored to different applications. In this context, the objective of this thesis is to achieve a thorough understanding on cell nucleation and growth phenomena that determine cell structures in plastic foaming processes. The core research strategy is to develop innovative visualization systems to capture and study these phenomena. A system with accurate heating and cooling control has been developed to observe and study crystallization-induced foaming behaviors of polymers under static conditions. The cell nucleation and initial growth behavior of polymers blown with different blowing agents (nitrogen, argon and helium, and carbon dioxide-nitrogen mixtures) have also been investigated in great detail. Furthermore, two innovative systems have been developed to simulate the dynamic conditions in industrial foaming processes: one system captures a foaming process under an easily adjustable and uniform extensional strain in a high temperature and pressure environment, while the other achieves the same target, but with shear strain. Using these systems, the extensional and shear effects on bubble nucleation and initial growth processes has been investigated independently in an isolated manner, which has never been achieved previously. The effectiveness of cell nucleating agents has also been evaluated under dynamic conditions, which have led to the identification of new foaming mechanisms based on polymer-chain alignment and generation of microvoids under stress. Knowledge generated from these researches and the wide range of future studies made possible by the visualization systems will be valuable to the development of innovative plastic foaming technologies and foams.