Browsing by Subject "rheology"
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Item Capillary thinning analysis(2022-01-03) Lauser, Kathleen T; Calabrese, Michelle A; mcalab@umn.edu; Calabrese, Michelle A; University of Minnesota Calabrese Research labThis collection of scripts is a package for analyzing extensional rheology data of liquid bridges. While this was created with Dripping-onto-Substrate datasets, this data analysis package may be useful for other liquid bridge thinning applications such as CaBER. Any pre-processing of images, such as binarizing, converting to png or cropping, can be completed with ImageJ.Item Dependence of Whole Blood Rheology on Oxygen Tension in Sickle Cell DIsease(2018-02) Lu, XinranIn sickle cell disease, oxygen tension plays a major role in dictating the mechanical function of single red blood cells. As oxygen tension decreases, cellular stiffness increases, to the point where the flow of whole blood can come to a compete occlusion. Unfortunately, there are also many unknowns in sickle cell disease, which is clinically expressed by the severe lack of approved treatment options for the disease. To solve many of these issues, we aim to expand our understanding of sickle cell disease by diving into the fundamental mechanisms by which the whole blood rheology becomes impaired in response to oxygen tension. Here, we use an in vitro disease model of sickle cell rheology, built within a microfluidic platform, to simulate whole blood flow within the microvasculature. We first report on the relationship between whole blood rheology and oxygen tension in sickle cell disease under steady state conditions and map out the specific oxygen tension where rheological impairment of blood flow begins. We then report on this measurement in both sickle cell trait (the heterozygous carrier state of sickle cell disease) as well as transfusion therapy in sickle cell disease, where we find and report on the rheological differences compared to native sickle cell disease. Next, we modify our microfluidic disease model to investigate the temporal and spatial dynamics of sickle cell disease by creating a microvascular capillary tree design couple to physiologically relevant oxygen tension gradients. Finally, we revisit the specific response of whole blood rheology as a function of oxygen tension by mapping out the velocity gradients and velocity profiles of blood flow, where we find characteristic differences in velocity profile shapes relative to oxygen.Item The Effects of Therapeutic Strategies in Restoring Sickle Cell Disease Blood Rheology(2022-04) Hansen, ScottSickle cell disease is a hereditary disease of the hemoglobin with devastating acute and chronic complications. The pathological polymerization of sickle hemoglobin during hypoxia reduces red blood cell deformability and increases blood viscosity. These biophysical changes to the red blood cells and whole blood rheology can obstruct blood flow and contribute to vaso-occlusion in the microcirculation. Though the genetic and molecular basis for the disease has been understood for decades, limited treatment options are available to those who suffer from this disease. Microfluidic platforms provide a physiologically relevant pre-clinical model to assess the response of sickle cell blood rheology to therapeutic strategies in vitro. This work focuses on the roles of affinity modifying compounds and high expression of fetal hemoglobin in inhibiting sickle hemoglobin polymerization and restoring healthy blood rheology. Isolating the biophysical effects of these therapeutic strategies on blood flow provides a better understanding of their mechanisms of action that may be of clinical significance. Microfluidic studies of sickle cell disease blood flow may help accelerate drug development and improve patient outcomes.Item Improvement of low fat Cheddar cheese texture using whey protein isolate aggregates(2015-02) Erickson, MollyTwo microparticulated whey protein fat mimetics were developed using the addition of lambda carrageenan to reduce whey protein aggregate size to approximately 2-10um. Interactions between the lamdba carrageenan and whey protein were analyzed using SDS-PAGE. Results suggest lambda carrageenan is not bound to the whey protein and that the aggregates were stabilized by disulfide bonding between the proteins. The fat mimetics were added to low fat Cheddar cheese at two addition rates and tested at one and two months of aging. Addition of fat mimetics produced a weaker cheese gel and produced no improvements in textural qualities as analyzed using rheological techniques. Low additions of fat mimetic produced a firmer texture. Though not significantly different than the low fat control, high addition rates of fat mimetic showed promise in improving texture, and confocal microscopy images suggest a disruption of protein structure with the high addition rates.Item The influence of hydrogen, deformation geometry, and grain size on the rheological properties of olivine at upper mantle conditions(2015-09) Tielke, JacobMany important geophysical processes, including mantle convection and the associated movement of Earth's tectonic plates, are strongly dependent upon the rheological properties of Earth's upper mantle. Olivine is the most abundant mineral in the upper mantle and therefore largely controls the mechanical behavior of this region of Earth's interior. Many experimental investigations have been carried out to study the rheological properties of olivine single crystals, synthetically produced aggregates, and naturally occurring mantle rocks at asthenospheric temperatures. In contrast, relatively few studies have focused on measuring the rheological properties of olivine deforming at lithospheric temperatures. Furthermore, there are several unanswered questions about the microphysical processes that control deformation of olivine at upper mantle conditions. One outstanding question in the field of rock and mineral physics is "Do different microphysical processes control the rate of deformation of olivine at asthenospheric compared to lithospheric mantle conditions?" To address this question we carried out direct shear experiments on olivine single crystals at temperatures that span the transition from lithospheric to asthenospheric mantle conditions. The results of these experiments, which are presented in Chapter 2, demonstrate that the dependence of strain rate upon stress transitions from a power-law relationship at high temperatures to an exponential dependence at lower temperatures. This transition in rheological behavior is consistent with deformation that is controlled by the climb of dislocations at high-temperature conditions and deformation that is controlled by the glide of dislocations at low-temperature conditions. Furthermore, the direct shear geometry allows for isolation of the (001)[100] and (100)[001] dislocation slip systems, which cannot be individually activated in triaxial compression. At high-temperature conditions, crystals oriented for shear on the (001)[100] slip system are observed to be weaker than crystals oriented for shear on the (100)[001] slip system. At low-temperature conditions the opposite relationship is observed: crystals oriented for shear on the (100)[001] slip system are weakest. Another important outstanding question is "Do the mechanisms of hydrolytic weakening in olivine differ at asthenospheric compared to lithospheric mantle conditions?" In Chapter 3 we report the results of experiments carried out on olivine single crystals under hydrous conditions at both asthenospheric and lithospheric temperatures. For crystals deformed at high-temperatures and under hydrous conditions, the dependence of strain rate on stress follows a power-law relationship with a stress exponent (n) of ~2.5, consistent with deformation that is rate limited by diffusion of silicon through the olivine lattice. In contrast, crystals deformed at high-temperatures and under anhydrous conditions yield n values of ~3.5, consistent with deformation that is rate limited by diffusion of silicon through the cores of dislocations. At low temperature conditions, the strain rate of both hydrous and anhydrous crystals are equally well described by the same exponential dependence of stress. These observations demonstrate significant hydrolytic weakening occurs at asthenospheric temperatures, but hydrolytic weakening cannot be resolved at lithospheric temperatures for our experimental conditions. Lastly, we address a question about polycrystalline deformation: "What deformation mechanism is responsible for grain-size sensitive (GSS) power-law creep of olivine aggregates?" In Chapter 4 we compare strain rates measured during deformation experiments on olivine aggregates to strain rates calculated from a micromechanical model of intragranular slip. The micromechanical model uses the measured stress from deformation experiments and grain orientations determined from post-deformation electron backscatter diffraction measurements to approximate the contribution of dislocation creep to the strain rate. Olivine aggregates deform up to a factor of 4.6 times faster than the maximum possible rates determined from the micromechanical model of intragranular slip. The ratio of experimentally determined strain rates to those from the micromechanical model is strongly dependent upon grain size, but is independent of stress and strength of lattice-preferred orientation. These observations indicate that GSS power-law creep occurs in both weakly and strongly textured olivine aggregates at the studied conditions. We consider three explanations for the observed rheological behavior, (1) a combination of diffusion and dislocation creep, (2) the operation of dynamic recrystallization creep, and (3) the operation of dislocation-accommodated grain-boundary sliding. Our analyses indicate that the microstructural and mechanical behavior of olivine aggregates deforming in the grain-size sensitive power-law regime are most consistent with the operation of dislocation-accommodated grain-boundary sliding at the studied experimental conditions.Item Novel Properties and Emergent Collective Phenomena of Active Fluids(2021-01) Liu, ZhengyangAn active fluid denotes a suspension of particles, cells and macromolecules that are capable of transducing free energy into systematic motions. Converting energy at individual constituent scales, these systems are constantly driven out of equilibrium and display unusual phenomena, including a transition to a zero viscosity superfluid-like state and a transition to a collective moving turbulent state. These curious transitions are consequences of the self-propulsion of active particles, and are absent in classical complex fluids without spontaneous motions. In this thesis, we present an experimental investigation on the rheology of active fluids under confinement. Specifically, we find the viscosity of bacterial suspensions is significantly reduced by confining walls. We show that this effect results from upstream swimming bacteria near the confining walls, which collectively exert stress on the fluids and push the fluids to flow. A phenomenological model is proposed which qualitatively captures the confinement effect on the viscosity of bacterial suspensions. The collective motions in dense bacterial suspensions are investigated. In particular, we measure the critical conditions of the transition from disordered state to turbulent state in bacterial suspensions. We present the experimental results in a phase diagram, serving as a benchmark for existing and future theories. We put forward a heuristic model based on two-body hydrodynamic interactions, hoping to understand the transition in a more intuitive way and to stimulate theoretical advancement. In addition, we present the first experimental study on the giant number fluctuation - a landmark of collectively moving active particles - in 3-dimensional bacterial suspensions. Our measurements are free from effect of frictional walls and thus allow quantitative comparison with previous theoretical and computational works. We also present a detailed analysis on the flow fields generated by the swimming bacteria, and reveal a strong coupling between flow strength and giant number fluctuations spanning all length scales. By elucidating the causes and consequences these phenomena, we not only expand the knowledge of active fluids, but also provide deeper understandings on the biological and ecological significance of living organism behavior. Our experiments deepen understanding of the self-organization processes in active fluids and lay the foundation of engineering machines composed of active constituents which mimics the properties of real living matter.Item Rheological Design of Sustainable Block Copolymers(2016-08) Mannion, AlexanderBlock copolymers are extremely versatile materials that microphase separate to give rise to a rich array of complex behavior, making them the ideal platform for the development of rheologically sophisticated soft matter. In line with growing environmental concerns of conventional plastics from petroleum feedstocks, this work focuses on the rheological design of sustainable block copolymers - those derived from renewable sources and are degradable - based on poly(lactide). Although commercially viable, poly(lactide) has a number of inherent deficiencies that result in a host of challenges that require both creative and practical solutions that are cost-effective and amenable to large-scale production. Specifically, this dissertation looks at applications in which both shear and extensional rheology dictate performance attributes, namely chewing gum, pressure-sensitive adhesives, and polymers for blown film extrusion. Structure-property relationships in the context of block polymer architecture, polymer composition, morphology, and branching are explored in depth. The basic principles and fundamental findings presented in this thesis are applicable to a broader range of substances that incorporate block copolymers for which rheology plays a pivotal role.Item Rheological Study of Particle-Laden Fluid Interfaces with a Custom-Built Rheometer(2023-04) Qiao, YimingUnderstanding the dynamics and mechanical properties of complex fluid-fluid interfaces is of great importance in various industrial applications such as food processing, drug delivery, and coating. In this thesis, my research efforts focus on studying the interfacial rheology of particle-laden fluid interfaces with a custom-built device. Despite the high demand for the characterization of interfacial rheology in academic and industrial research, the study of interfacial rheology is still scarce compared to its counterpart of bulk rheometry and is limited only to specialized laboratories. One of biggest hurdles impeding the broad application of interfacial rheometry is the delicate design and the high cost of interfacial rheometers. In the first part of the thesis, a novel apparatus of the in-situ interfacial rheometer would be introduced. The simple design substantially reduces its dimension, making the new device highly portable and cost-effective for any laboratories that have access to optical microscopes for a wide range of interfacial rheology studies. Using the newly-developed interfacial rheometer, we study the rheology and microstructure of particle-laden fluid interfaces. In particular, the possibility of using Janus particles to tune the rheological response of particle-laden fluid interfaces is explored. Janus particles are heterogeneous colloids composed of two or more distinct regions with different surface properties. We find that the addition of a small amount of Janus particles can lead to a significant increase in surface moduli with enhanced elasticity, which greatly improves the stability of the interface. This drastic change in interfacial rheology is associated with the formation of local particle clusters surrounding each Janus particle. The origin of particle clusters is explained by considering the interparticle interactions at the interface. These experiments demonstrate a new way to tune the microstructure and mechanical properties of fluid-fluid interfaces. We then relate the microscopic dynamics of those particle clusters to their profound effects on the macroscopic rheology of particle-laden interfaces. By analyzing the local affine deformation of particles, we show that particles in those localized clusters experience substantially lower shear-induced stretching than their neighbors outside clusters. Such heterogeneous dynamics increase the effective surface coverage of particles, which in turn enhance the moduli of the interface, consistent with direct interfacial rheological measurements. Our findings open up an avenue for designing interfacial materials with improved mechanical properties via the control of the formation of localized particle clusters.Item Shear-Banding In Entangled Polymer Solutions Under Large Amplitude Oscillatory Shear: A Confocal Rheometry Study(2020-04) Shin, SeunghwanWe use a large aspect-ratio, planar-Couette shear cell to explore the flow properties of entangled polymer solutions, with a special focus on a long-standing problem of shear-banding in polymer solutions/melts. We first analyze the velocity profiles of entangled DNA solutions under large amplitude oscillatory shear (LAOS) inside the shear cell. We vary a gap between the shearing plates and Weissenberg number ($\mathrm{Wi}$) to construct phase diagrams quantifying the degree of wall-slip and shear-banding at different conditions. We observe transitions from normal linear shear profiles to wall-slip dominant and finally to shear-banding profiles with increasing $\mathrm{Wi}$. We further explore the dynamics of micron-sized tracer particles embedded in the solutions to study the microscopic origin of the shear-banding. Tracer particles in the shear frame exhibit transient super-diffusivity and strong dynamic heterogeneity localized in the high-shear-rate band. The probability distribution functions of particle displacements follow a power-law scaling at large displacements, indicating a L\'{e}vy-walk-type motion, reminiscent of tracer dynamics in entangled wormlike micelle solutions and sheared colloidal glasses. We further characterize the length and time scales of the abnormal dynamics of tracer particles. Based on them, we hypothesize that the unusual particle dynamics arise from localized shear-induced chain disentanglement. Next, we experimentally investigate a penetration of edge-induced disturbances and its influence on shear-banding flows. Edge instabilities have been pointed out as one of the possible experimental artifacts leading to apparently heterogeneous shear profiles. Simulations suggested even a mild edge disturbance can penetrate deeply along a vorticity direction to cause apparent gradient-banding of a velocity profile, potentially misleading experimentalists. We measure velocity profiles at different locations to reveal penetrating behavior of edge disturbances and test authenticity of the observed shear-banding flows. Under a weak oscillatory shear ($\mathrm{Wi} < 1$) where DNA solutions display a linear shear profile with wall slip, the penetration depth of the edge disturbance was on the order of the gap thickness , similar to a behavior in Newtonian fluids. Under a strong shear ($\mathrm{Wi} > 1$) where shear-banding flows are developed, the penetration depth was estimated as 20 $H$ along the flow direction while it was still on the order of the gap thickness along the vorticity direction. Furthermore, we find that the shear-banding profiles persist deep inside the sheared fluid, where the influence of edge disturbances diminishes. Our findings suggest a long penetration of the edge disturbance and also demonstrates the authentic nature of the observed shear-banding polymers. Shear-induced microscopic conformational change of individual polymer chains that trigger shear banding still remains an open question. To attain information about chain-end distributions and its dynamics, we synthesize dumbbells consisting of two spherical colloidal tracer particles connected by $\lambda$-DNA linkers and track their 2D-projected configurations and motions in the two shear-bands. We observe preferable alignment along the flow direction, enhanced translation/rotation in the high-shear-rate band. Coupling between translational/rotational dynamics and stronger correlation between chain extension and translation are also found in the high-shear-rate band. We hypothesize a formation of the localized low viscosity zones which allow the enhanced dynamics and chain extension in the high-shear-rate band.Item Supporting data for Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers(2018-02-06) Haugan, Ingrid N; Maher, Michael J; Chang, Alice B; Lin, Tzu-Pin; Grubbs, Robert H; Hillmyer, Marc A; Bates, Frank S; bates001@umn.edu; Bates, Frank SThese files contain data along with associated output from instrumentation supporting all results reported in Haugan et. al. "Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers." In Haugan et. al. we found: The linear viscoelastic behavior of poly(norbornene)-graft-poly(±-lactide) was investigated as a function of grafting density and overall molar mass. Eight sets of polymers with grafting densities ranging from 0–100% were synthesized by living ring-opening metathesis copolymerization. Within each set, the graft chain molar mass and spacing between grafts were fixed while the total backbone length was varied. Dynamic master curves reveal that these polymers display Rouse and reptation dynamics with a sharp transition in the zero-shear viscosity data demonstrating that grafting density strongly impacts the entanglement molar mass. The entanglement modulus (Ge) scales with inverse grafting density (ng) as Ge ~ ng1.2 and Ge ~ ng0 in accordance with scaling theory in the high and low grafting density limits, respectively. However, a sharp transition between these limiting behaviors occurs, which does not conform to existing theoretical models for graft polymers. A molecular interpretation based on thin flexible chains at low grafting density and thick semiflexible chains at high grafting density anticipates the sharp transition between the limiting dynamical regimes.Item Supporting data for Preparation and characterization of H-shaped polylactide(2024-05-16) Zografos, Aristotelis; Maines, Erin, M; Hassler, Joseph, F; Bates, Frank, S; Hillmyer, Marc, A; hillmyer@umn.edu; Hillmyer, Marc, A; University of Minnesota Department of ChemistryThese files contain primary data along with associated output from instrumentation supporting all results reported in Zografos et al. Preparation and Characterization of H-Shaped Polylactide. In Zografos et al. we developed an efficient strategy for synthesizing H-polymers. An H-polymer has an architecture that consists of four branches symmetrically attached to the ends of a polymer backbone, similar in shape to the letter ‘H’. Here, a renewable H-polymer efficiently synthesized using only ring-opening transesterification is demonstrated for the first time. The strategy relies on a tetrafunctional poly(±-lactide) macroinitiator, from which four poly(±-lactide) branches are grown simultaneously. Proton nuclear magnetic resonance (1H-NMR) spectroscopy, size exclusion chromatography (SEC), and matrix assisted laser desorption/ionization (MALDI) spectrometry were used to verify the macroinitiator purity. Branch growth was probed using 1H-NMR spectroscopy and SEC to reveal unique transesterification phenomena that can be controlled to yield architecturally pure or more complex materials. H-shaped PLA was prepared at the grams scale with a weight average molar mass Mw > 100 kg/mol and narrow dispersity Ð < 1.15. Purification involved routine precipitations steps, which yielded products that were architecturally relatively pure (~93%). Small-amplitude oscillatory shear and extensional rheology measurements were used to demonstrate the unique viscoelastic behavior associated with the H-shaped architecture.