A computer-controlled microfluidic extensional flow device is developed for trapping and manipulating micron-sized hard and soft particles. The extensional flow is generated in a diamond-shaped cross-slot that has each corner connected to a pressure-controlled liquid reservoir. By employing an imaging-based control algorithm, a particle can be made to move to an arbitrary position within the slot by adjusting the reservoir pressures and hence the fluid flow rates into/out of the slot. Thus, a soft particle can be trapped indefinitely at a point within the slot, and a known hydrodynamic force can be applied to study the dynamics of stretching and breakup of the particle. Alternatively, adhesion or coalescence dynamics of soft particles may be investigated by effecting a controlled collision between two particles. The device is validated by measuring the low interfacial tension of a compatibilized oil-water interface.

A computer-controlled microfluidic extensional flow device is developed for trapping and manipulating micron-sized hard and soft particles. The extensional flow is generated in a diamond-shaped cross-slot that has each corner connected to a pressure-controlled liquid reservoir. By employing an imaging-based control algorithm, a particle can be made to move to an arbitrary position within the slot by adjusting the reservoir pressures and hence the fluid flow rates into/out of the slot. Thus, a soft particle can be trapped indefinitely at a point within the slot, and a known hydrodynamic force can be applied to study the dynamics of stretching and breakup of the particle. Alternatively, adhesion or coalescence dynamics of soft particles may be investigated by effecting a controlled collision between two particles. The device is validated by measuring the low interfacial tension of a compatibilized oil-water interface.

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.

The influence of turbulence on the orientation state of a dilute suspension of stiff fibers at high Reynolds number in a planar contraction is investigated. High speed imaging and LDV techniques are used to quantify fiber orientation distribution and turbulent characteristics. A nearly homogenous, isotropic grid generated turbulent flow is introduced at the contraction inlet. Flow Reynolds number and inlet turbulent characteristics are varied in order to determine their effects on orientation distribution. The orientation anisotropy is shown to be accurately modelled by a Fokker-Planck type equation. Results show that rotational diffusion is highly influenced by inlet turbulent characteristics and decays exponentially with convergence ratio. Furthermore, the effect of turbulent energy production in the contraction is shown to be negligible. Also, the results show that the flow Reynolds number has negligible effect on the development of orientation anisotropy, and the influence of turbulence on fiber rotation is negligible for $mathrm{Pe_r}>$ 10. It was concluded that inertia induced fiber motion played a negligible role in the experiments.

A filament stretching extensional rheometer was used to investigate the effect of uniaxial flow on the crystallization of polypropylene. Samples were heated to a temperature above the melt temperature to erase their thermal and mechanical histories. The Janeschitz-Kriegl protocol was applied and samples were stretched at various extension rates to a final strain of e = 3.0. Differential scanning calorimetry was applied to crystallized samples to measure the degree of crystallinity. The results showed that a minimum extension rate, corresponding to a Weissenberg number of approximately Wi = 1, is required for an increase in percent crystallization to occur. Below this Weissenberg number, the flow is not strong enough to align the tubes of constrained polymer chains and as a result there is no change in the final percent crystallization. An extension rate was also found for which percent crystallization is maximized. The increase in crystallinity is likely due to flow-induced orientation and alignment of tubes of constrained polymer chains. Polarized-light microscopy verified an increase in number and decrease in size of spherulites with increasing extension rate. Small angle X-ray scattering showed a 7% decrease in inter-lamellar spacing at the transition to flow-induced increase in crystallization. Crystallization kinetics were examined by observing the time required for melts to crystallize under uniaxial flow. The crystallization time decreased with increasing extension rate, even for extension rates where no increase in percent crystallization was observed. These results demonstrate that the speed of crystallization kinetics is greatly enhanced by the application of extensional flow.

This dissertation establishes a mathematical framework for analyzing a viscoelastic model that displays thixotropic behavior as a model parameter gets very small. The model is the partially extending strand convection model, originally derived for polymeric melts that have long strands that get in the way of fully retracting. A Newtonian solvent is added. The uniaxial and equibiaxial extensional flows are studied using combined asymptotic analysis and numerical simulations. An initial value problem with a prescribed elongational stress is solved in the limit of large relaxation time. This gives rise to multiple time scales. If the initial stress is less than a critical value, the initial elastic elongation is followed by settling to an unyielded state at the slow time scale. If the initial stress is larger than the critical value, then yielding ensues. The extensional flows produce delayed yielding and hysteresis, both associated with thixotropy in complex fluids. / Ph. D.

Non-spherical particles are present all around us, in biological, industrial and environmental processes. Making predictions of their impact on us and systems in our vicinity can make life better for everyone here on earth. For example, the ash particles from a volcano eruption are non-spherical and their spreading in the atmosphere can hugely impact the air traffic, as was also proven in 2010. Furthermore, the orientation of the wood fibres in a paper sheet influences the final properties of the paper, and the cause of a specific fibre orientation can be traced back to the fluid flows during the manufacturing process of the paper. In this thesis, experimental and numerical work is presented with the goal to understand and utilize the behavior of elongated particles in fluid flows. Two different experimental setups are used. The first one, a turbulent half channel flow, aims at increasing the understanding of how particles with non-zero inertia behave in turbulence. The second setup is an attempt to design a flow field with the purpose to align nanofibrils and create high performance cellulose filaments. Experiments were performed in a turbulent half channel flow at different flow set- tings with dilute suspensions of cellulose acetate fibres having three different aspect ratios (length to width ratio). The two main results were firstly that the fibres agglom- erated in streamwise streaks, believed to be due to the turbulent velocity structures in the flow. Secondly, the orientation of the fibres was observed to be determined by the aspect ratio and the mean shear, not the turbulence. Short fibres were oriented in the spanwise direction while long fibres were oriented in the streamwise direction. In order to utilize the impressive properties (stiffness comparable to Kevlar) of the cellulose nanofibril in a macroscopic material, the alignment of the fibrils must be controlled. Here, a flow focusing device (resulting in an extensional flow), designed to align the fibrils, is used to create a cellulose filament with aligned fibrils. The principle is based on a separation of the alignment and the assembly of the fibrils, i.e. first align the fibrils and then lock the aligned structure. With this process, continuous filaments were created, with properties similar to that of the wood fibre at the same fibril alignment. However, the highest alignment (lowest angle) of the fibrils in a filament created was only 31o from the filament axis, and the next step is to increase the alignment. This thesis includes modeling of the alignment process with the Smoluchowski equation and a rotary diffusion. Finding a model that correctly describes the alignment process should in the end make it possible to create a filament with fully aligned fibrils. / <p>QC 20140908</p>

Neste trabalho estudou-se o comportamento reológico e morfológico da mistura polimérica imiscível de polipropileno e poliamida. Como resultado deste estudo obtiveram-se valores de tensão interfacial entre 10mN/m e 13mN/m. A tensão interfacial diminuiu em até 87% quando a mistura é compatibilizada com polipropileno maleado. A análise morfológica no regime de viscoelasticidade linear quando avaliada uma morfologia de emulsão de poliamida em polipropileno revelou diâmetro médio da fase dispersa entre 1,5µm e 20µm. O diâmetro das gotas da fase dispersa diminuiu com a adição de polipropileno maleado chegando a reduções de até 98%, mantendo-se constante a concentração da fase dispersa. No regime de viscoelasticidade não linear foram testados modelos para avaliar o comportamento da mistura em fluxos de cisalhamento e extensão, sendo que somente para os fluxos de extensão foi obtida boa correlação dos resultados experimentais com as previsões teóricas. / Rheological and morphological behaviour of polypropylene and polyamide polymer blend was studied. The values of interfacial tension were obtained between 10mN/m and 13mN/m. The interfacial tension decreased in 87% for compatibilized blend. Morphology analysis for linear viscoelastic regime shows dispersed drop diameter between 1,5µm and 20µm. The diameter of the drops decreased with the addition of maleic polypropylene reducing until 98%, keeping constant the concentration of the disperse phase. In non linear viscoelastic regime different models were tested to evaluate the behavior of the blends in shear and elongacional flows. However, only the elongacional flow results were acquired with theoretical - experimental corroboration.

Neste trabalho estudou-se o comportamento reológico e morfológico da mistura polimérica imiscível de polipropileno e poliamida. Como resultado deste estudo obtiveram-se valores de tensão interfacial entre 10mN/m e 13mN/m. A tensão interfacial diminuiu em até 87% quando a mistura é compatibilizada com polipropileno maleado. A análise morfológica no regime de viscoelasticidade linear quando avaliada uma morfologia de emulsão de poliamida em polipropileno revelou diâmetro médio da fase dispersa entre 1,5µm e 20µm. O diâmetro das gotas da fase dispersa diminuiu com a adição de polipropileno maleado chegando a reduções de até 98%, mantendo-se constante a concentração da fase dispersa. No regime de viscoelasticidade não linear foram testados modelos para avaliar o comportamento da mistura em fluxos de cisalhamento e extensão, sendo que somente para os fluxos de extensão foi obtida boa correlação dos resultados experimentais com as previsões teóricas. / Rheological and morphological behaviour of polypropylene and polyamide polymer blend was studied. The values of interfacial tension were obtained between 10mN/m and 13mN/m. The interfacial tension decreased in 87% for compatibilized blend. Morphology analysis for linear viscoelastic regime shows dispersed drop diameter between 1,5µm and 20µm. The diameter of the drops decreased with the addition of maleic polypropylene reducing until 98%, keeping constant the concentration of the disperse phase. In non linear viscoelastic regime different models were tested to evaluate the behavior of the blends in shear and elongacional flows. However, only the elongacional flow results were acquired with theoretical - experimental corroboration.

Les particules soumises à un écoulement peuvent manifester des orientations préférées et une variété de déformations en fonction de leur géométrie et élasticité et du champ de vitesse de l'écoulement. A l’inverse, les flux peuvent être modifiés lorsque les contraintes des particules sont non négligeables. Cette thèse présente des résultats théoriques et numériques sur cette relation bilatérale en deux parties. La Ière partie commence par une analyse de stabilité et des simulations numériques qui montrent une particule brownienne semi-flexible dans un écoulement élongationnel effectuant un retournement, un phénomène associé aux flux de cisaillement. Le Chap. 2 étend les outils analytiques dédiés aux modèles simples ou aux flux indépendante du temps pour les modèles perle-barre-bond généraux dans les flux aléatoires. En partant des résultats des chapitres précédents, Le Chap. 3 aboutit à l'étude d'un degré de liberté lagrangien inexploré dans un écoulement turbulent : la flexion. Une particule semi-flexible courbe différemment dans les flux aléatoires bidimensionnels et tridimensionnels. La IIème partie concerne la turbulence élastique, un régime chaotique créé dans un écoulement de faibles forces inertielles par l'ajout de polymères élastiques. Le Chap. 4 estime le nombre de degrés de liberté d'une solution de ce régime via la dimension Lyapunov de l'attracteur du modèle Oldroyd-B bidimensionnel, un modèle connu de reproduire la turbulence élastique dans les simulations numériques. Le Chap. 5 pose des questions sur la nécessité d'élasticité pour produire un régime chaotique et conclut qu'une solution de polymère de barres peut créer un régime comparable à la turbulence élastique. / Particles, when subjected into a flow, may display preferred orientations and a variety of deformations depending on their geometry and elasticity and the flow velocity field. Flows can conversely be modified when the particle stresses are sufficiently large. This thesis presents theoretical and numerical results on this two-way relationship between particles and flows in two parts. Part I starts with a stability analysis and numerical simulations that show a simple semiflexible Brownian particle in an extensional flow undergo tumbling, a phenomenon normally associated to shear flows. Chapter 2 extends analytical tools available only for elementary polymer models or for steady flows to general bead-rod-spring models in random flows. By building on the results from the previous chapters, Chap. 3 culminates with the study of an unexplored Lagrangian degree of freedom in a turbulent flow: bending. A semiflexible particle is shown to display different bending behaviours in two- and three-dimensional random flows. This prediction is confirmed via direct numerical simulations of the particle in a turbulent flow. Part II concerns “elastic turbulence", a chaotic regime created in a flow with low inertial forces by the addition of elastic polymers. Chapter 4 provides an estimate for the number of degrees of freedom of a solution of this chaotic system via the Lyapunov dimension of the attractor of the two-dimensional Oldroyd-B model, a model known to reproduce elastic turbulence in numerical simulations. Chapter 5 questions the necessity of elasticity in producing a chaotic regime and concludes that a rodlike polymer solution can create a regime similar to elastic turbulence.