The Experts below are selected from a list of 8622 Experts worldwide ranked by ideXlab platform
Gareth H. Mckinley - One of the best experts on this subject based on the ideXlab platform.
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Rheology as a Mechanoscopic Method to Monitor Mineralization in Hydrogels
2017Co-Authors: Abigail U. Regitsky, Gareth H. Mckinley, Bavand Keshavarz, Niels Holten-andersenAbstract:Biominerals have been widely studied due to their unique mechanical properties, afforded by their inorganic–organic composite structure and well-controlled growth in macromolecular environments. However, a lack of suitable characterization techniques for inorganic minerals in organic-rich media has prevented a full understanding of biomineralization. Here, we applied Rheometry to study mineral nucleation and growth dynamics by measuring viscoelastic material properties of a hydrogel system during mineralization. Our proof-of-concept system consists of a gelatin hydrogel matrix preloaded with calcium ions and a reservoir of carbonate ions, which diffuse through the gel to initiate mineralization. We found that gels with diffused carbonate show an increase in low frequency energy dissipation, which scales with carbonate concentration and gel pH. Using this signal, and recognizing that mineralization occurs simultaneously with carbonate diffusion in our system, we have mechanoscopically tracked mineral growth in situ, showcasing the potential of Rheometry for studying mineralization kinetics in real time
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Optimized cross-slot flow geometry for microfluidic extensional Rheometry.
Physical review letters, 2012Co-Authors: Simon J. Haward, Monica Oliveira, Manuel A. Alves, Gareth H. MckinleyAbstract:A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point streamline, and we observe the formation of a strong and uniform birefringent strand when the dimensionless flow strength exceeds a critical Weissenberg number Wicrit 0:5. Birefringence and bulk pressure drop measurements provide self consistent estimates of the planar extensional viscosity of the fluid over a wide range of deformation rates (26 s1 "_ 435 s1) and are also in close agreement with numerical simulations performed by using a finitely extensible nonlinear elastic dumbbell model.
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Optimized Cross-Slot Flow Geometry for Microfluidic Extensional Rheometry
'American Physical Society (APS)', 2012Co-Authors: Simon J. Haward, Manuel A. Alves, Mónica S. N. Oliveira, Gareth H. MckinleyAbstract:A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point streamline, and we observe the formation of a strong and uniform birefringent strand when the dimensionless flow strength exceeds a critical Weissenberg number Wi(crit) approximate to 0.5. Birefringence and bulk pressure drop measurements provide self-consistent estimates of the planar extensional viscosity of the fluid over a wide range of deformation rates (26 s(-1)
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tribo Rheometry from gap dependent rheology to tribology
Tribology Letters, 2004Co-Authors: H P Kavehpour, Gareth H. MckinleyAbstract:We describe a new tribo-Rheometry fixture that can be utilized with a commercial torsional rheometer in order to explore the coupled rheological and tribological properties of complex fluids and solid–liquid systems. The fixture is self-leveling and both the normal load and the sample gap can be monitored or controlled. At large gaps, the fixture imposes an approximately constant shear rate on the sample and the bulk viscometric properties of the fluid can be measured. However, as the gap between the plates is reduced, the measured viscosity function becomes gap-dependent. For gaps on the order of the surface roughness of the plates, the device is operated under a constant applied load and the tribological properties of the fluid–solid pair can then be measured. Using this new tribo-rheometer fixture it is possible to obtain tribological information over a wider range of sliding velocities than is typically possible using conventional devices such as pin-and-disk systems. The data can be represented in the form of a classical Stribeck diagram or, by using a dimensionless gap-dependent shift factor, it is possible to construct a more general “friction map” of the gap- and load-dependent effective viscosity (Luengo et al. Wear 200 (1996)). The capabilities of this system are illustrated using a number of different lubricant fluids, for a range of normal stresses and variations in surface properties such as the mean roughness.
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filament stretching Rheometry of complex fluids
Annual Review of Fluid Mechanics, 2002Co-Authors: Gareth H. Mckinley, Tamarapu SridharAbstract:▪ Abstract Filament-stretching rheometers are devices for measuring the extensional viscosity of moderately viscous non-Newtonian fluids such as polymer solutions. In these devices, a cylindrical liquid bridge is initially formed between two circular end-plates. The plates are then moved apart in a prescribed manner such that the fluid sample is subjected to a strong extensional deformation. Asymptotic analysis and numerical computation show that the resulting kinematics closely approximate those of an ideal homogeneous uniaxial elongation. The evolution in the tensile stress (measured mechanically) and the molecular conformation (measured optically) can be followed as functions of the rate of stretching and the total strain imposed. The resulting rheological measurements are a sensitive discriminant of molecularly based constitutive equations proposed for complex fluids. The dynamical response of the elongating filament is also coupled to the extensional rheology of the polymeric test fluid, and this can...
Simon J. Haward - One of the best experts on this subject based on the ideXlab platform.
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microfluidic extensional Rheometry using stagnation point flow
Biomicrofluidics, 2016Co-Authors: Simon J. HawardAbstract:Characterization of the extensional Rheometry of fluids with complex microstructures is of great relevance to the optimization of a wide range of industrial applications and for understanding various natural processes, biological functions, and diseases. However, quantitative measurement of the extensional properties of complex fluids has proven elusive to researchers, particularly in the case of low viscosity, weakly elastic fluids. For some time, microfluidic platforms have been recognized as having the potential to fill this gap and various approaches have been proposed. This review begins with a general discussion of extensional viscosity and the requirements of an extensional rheometer, before various types of extensional rheometers (particularly those of microfluidic design) are critically discussed. A specific focus is placed on microfluidic stagnation point extensional flows generated by cross-slot type devices, for which some important developments have been reported during the last 10 years. Additional emphasis is placed on measurements made on relevant biological fluids. Finally, the operating limits of the cross-slot extensional rheometer (chiefly imposed by the onset of elastic and inertial flow instabilities) are discussed.
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Optimized cross-slot flow geometry for microfluidic extensional Rheometry.
Physical review letters, 2012Co-Authors: Simon J. Haward, Monica Oliveira, Manuel A. Alves, Gareth H. MckinleyAbstract:A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point streamline, and we observe the formation of a strong and uniform birefringent strand when the dimensionless flow strength exceeds a critical Weissenberg number Wicrit 0:5. Birefringence and bulk pressure drop measurements provide self consistent estimates of the planar extensional viscosity of the fluid over a wide range of deformation rates (26 s1 "_ 435 s1) and are also in close agreement with numerical simulations performed by using a finitely extensible nonlinear elastic dumbbell model.
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Optimized Cross-Slot Flow Geometry for Microfluidic Extensional Rheometry
'American Physical Society (APS)', 2012Co-Authors: Simon J. Haward, Manuel A. Alves, Mónica S. N. Oliveira, Gareth H. MckinleyAbstract:A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point streamline, and we observe the formation of a strong and uniform birefringent strand when the dimensionless flow strength exceeds a critical Weissenberg number Wi(crit) approximate to 0.5. Birefringence and bulk pressure drop measurements provide self-consistent estimates of the planar extensional viscosity of the fluid over a wide range of deformation rates (26 s(-1)
Jan Vermant - One of the best experts on this subject based on the ideXlab platform.
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Operating windows for oscillatory interfacial shear rheology
Journal of Rheology, 2020Co-Authors: Damian Renggli, Alexandra A. Alicke, Randy H. Ewoldt, Jan VermantAbstract:Interfacial rheology becomes important when surface active species such as surfactants, particles, or proteins are present in sufficient quantities at liquid-liquid interfaces and interact between them. Interfacial Rheometry measurements are challenging for various reasons. The mechanical response of the thin interface is often weaker compared to that of bulk materials and so one is often measuring close to the lower force and torque limits of rheometers, hence signal-to-noise ratios merit closer attention. In addition, the role of both instrument and sample inertia is more important for interfacial Rheometry compared to bulk Rheometry. Effects of misalignment and imperfections of the measurement geometries lead to effects of surface and line tension. Finally, peculiar for interfacial Rheometry is the need to deconvolute the contributions of flow and deformation in the surrounding phases from that at the interface. Whereas some of these aspects have received attention in previous works, a clear and unambiguous view on the operating limits of interfacial rheometers has been missing. In the present work, we investigate the different experimental challenges and develop a generic methodology, which provides a clear definition of the operating limits of various interfacial rheometers including the interfacial needle shear rheometer, the double wall ring, and the bicone geometries. We validate this methodology by investigating the limitations defined intrinsically by the instrument as well as the ones emerging from the properties of the interface of interest for an interface composed of fatty alcohols which represents a challenging test case. The results provide cautionary examples and clear guidelines for anyone measuring interfacial rheology with these direct rheological techniques.Interfacial rheology becomes important when surface active species such as surfactants, particles, or proteins are present in sufficient quantities at liquid-liquid interfaces and interact between them. Interfacial Rheometry measurements are challenging for various reasons. The mechanical response of the thin interface is often weaker compared to that of bulk materials and so one is often measuring close to the lower force and torque limits of rheometers, hence signal-to-noise ratios merit closer attention. In addition, the role of both instrument and sample inertia is more important for interfacial Rheometry compared to bulk Rheometry. Effects of misalignment and imperfections of the measurement geometries lead to effects of surface and line tension. Finally, peculiar for interfacial Rheometry is the need to deconvolute the contributions of flow and deformation in the surrounding phases from that at the interface. Whereas some of these aspects have received attention in previous works, a clear and unambi...
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predicting the apparent wall slip when using roughened geometries a porous medium approach
Journal of Rheology, 2015Co-Authors: Claudia Carotenuto, Anja Vananroye, Jan Vermant, Mario MinaleAbstract:A common approach to prevent or alleviate wall slip in rotational Rheometry is to utilize roughened geometries. While this is a helpful strategy, the presence of the surface roughness introduces a fundamentally different boundary condition, as the flow trough the porous structure needs to be accounted for. In the present work, we investigate the use of rough surfaces in Rheometry, starting with simple Newtonian fluids. Both structured and randomly structured surfaces are used, i.e., a cross-hatched plate and a sandpaper disk, respectively. We show that the fluid flows within the roughened layer and that the flow in the gap of the rheometer can be modeled as a flow over and through a porous medium. Stokes' equation and Brinkman's equation can be coupled at the interface through a suitable stress boundary condition recently developed in the literature that takes the momentum transfer to both the fluid and the solid substrate properly into account [Minale, Phys Fluids 26, 123102 (2014b)]. The predictions of ...
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extensional Rheometry at interfaces analysis of the cambridge interfacial tensiometer
Journal of Rheology, 2012Co-Authors: Tom Verwijlen, Jan Vermant, Danielle L Leiske, Paula Moldenaers, Gerald G FullerAbstract:Whereas devices for measuring the interfacial shear and dilatational rheology are readily available, extensional Rheometry at interfaces remains essentially unexplored. However, a setup mimicking a 2D filament stretching rheometer, the Cambridge Interfacial Tensiometer, was proposed for this very purpose [Jones and Middelberg, Chem. Eng. Sci. 57, 1711–1722 (2002)]. In the present work, a framework is presented for analyzing the interfacial flow field in such device for Newtonian interfaces in the presence of Marangoni flows. Based on the dimensionless numbers that govern the interfacial flow field, different dominant flow types can be identified and the sensitivity of the device for measuring the extensional interfacial viscosity is determined. For the flow field to be dominated by extensional deformations, either the Marangoni number or the ratio of dilatational viscosity to shear viscosity should be at least an order of magnitude higher than the Trouton ratio. Using an analysis for Newtonian materials, ...
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A double wall-ring geometry for interfacial shear Rheometry
Rheologica Acta, 2010Co-Authors: Steven Vandebril, Gerald G Fuller, Paula Moldenaers, Aly Franck, Jan VermantAbstract:The rheological properties of complex fluid interfaces are of prime importance in a number of technological and biological applications. Whereas several methods have been proposed to measure the surface rheological properties, it remains an intrinsically challenging problem due to the small forces and torques involved and due to the intricate coupling between interfacial and bulk flows. In the present work, a double wall-ring geometry to measure the viscoelastic properties of interfaces in shear flows is presented. The geometry can be used in combination with a modern rotational rheometer. A numerical analysis of the flow field as a function of the surface viscoelastic properties is presented to evaluate the non-linearities in the surface velocity profile at a low Boussinesq number. The sensitivity of the geometry, as well as its applicability, are demonstrated using some reference Newtonian and viscoelastic fluids. Oscillatory and steady shear measurements on these reference complex fluid interfaces demonstrate the intrinsic sensitivity, the accuracy, and the dynamic range of the geometry when used in combination with a sensitive rheometer.
Jose I Reyesdecorcuera - One of the best experts on this subject based on the ideXlab platform.
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pectinmethylesterase affects the flow behavior of orange pulp
Journal of Food Science, 2021Co-Authors: Jose I ReyesdecorcueraAbstract:In the orange juice industry, pulp (ruptured juice sacs) is separated from the juice after extraction and pasteurized separately before blending back with juice or sold for other food applications. However, pulp is not always pasteurized immediately after extraction and the flow behavior is affected by endogenous pectinmethylesterase (PME). This is particularly important because of the high power required to pump orange pulp in industrial pasteurizers. This study characterized the effect of PME on the flow behavior of citrus pulp during storage at 4 °C using rotational Rheometry and during pulp storage at 22 °C using capillary Rheometry. PME activity was 0.011 ± 0.001 PEU for the pulp used in rotational Rheometry and 0.030 ± 0.002 PEU for the pulp used in capillary Rheometry. Rotational Rheometry was used to assess the effect of PME on the Power Law parameters at shear rates ( γ ) below those that cause slip. There were no significant differences among storage time on the flow behavior index (n). However, the consistency coefficient (K) increased with storage time. Significant differences were found after 12-hr storage increasing from 120 ± 30 Pa·sn to 160 ± 15 Pa·sn (16.7%) after 24 hr. Capillary rheomtery was used to assess the effect of PME on the pressure drop in a flow system. Significant differences were found at or after 12-hr storage. The mean pressure drop increased by 34% after 24 hr, for a flow rate of 50 × 10-6 m3 /s (0.8 GPM) in an 8.9-m long (29.2 ft), 0.022-m (1-in) diameter pipe. PRACTICAL APPLICATION: Design and optimization of processing equipment and industrial handling systems of orange pulp require detailed knowledge of its rheological (flow) properties. Citrus pulp is rich in pectinmethylesterase, an enzyme that causes thickening of the product when not inactivated during pasteurization. Understanding how fast PME affects the flow properties of orange pulp is important for citrus processors to decide how long pulp can be stored before pasteurizing it.
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combined rotational and capillary rheomtery to determine slip coefficients and other rheological properties of orange pulp
Journal of Food Science, 2021Co-Authors: Elyse M Payne, Jose I ReyesdecorcueraAbstract:The characterization of the rheological properties of orange pulp under typical processing temperatures is needed for the design and optimization of orange pulp processing systems. The flow of orange pulp produced slip at shear rates at ∼1 to 5 s-1 . Rotational Rheometry revealed that the flow behavior of orange pulp before slip occurrence followed the Power Law model for concentrations of ∼500 to 800 g/L at 4 to 80 °C. The consistency coefficient (K) ranged from 33 to 234 Pa·sn and the flow behavior index n ranged from 0.18 to 0.24. Both, K and n decreased with temperature. While K fitted well an Arrhenius-like model, n best fitted a linear model. As concentration increased K increased linearly, while n was not significantly (P > 0.05) affected. The flow without slip was calculated using the Power Law parameters from rotational Rheometry and the wall shear stress (σw ) from capillary Rheometry for the experimental flow rates. This allowed calculating the corrected slip coefficient βc and obviated the need for pipes with multiple diameters. βc decreased by one order of magnitude when temperature increased from 4 to 50 °C when σw was 0.1 kPa. The effect was exacerbated with increased flow rate. Similarly, βc increased by about one order of magnitude when pulp concentration increased from ∼550 to 850 g/L at 80 °C. The increase in βc with temperature indicated that the effect of temperature in the consistency of the bulk was different from its effect on the consistency of the liquid phase near the pipe wall. PRACTICAL APPLICATION: Design and optimization of processes equipment and industrial handling systems of orange pulp require detailed knowledge of their rheological (flow) properties. Citrus pulp like fruit pastes and purees produce less friction than one would anticipate when they flow because the liquid fraction acts as a lubricant. This study presents an original method for such characterization and shows that wall slip is greatly affected by temperature and concentration.
Eric Brown - One of the best experts on this subject based on the ideXlab platform.
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effect of oxidation on the mechanical properties of liquid gallium and eutectic gallium indium
Physics of Fluids, 2012Co-Authors: Nikolai Oudalov, Qiti Guo, Heinrich M Jaeger, Eric BrownAbstract:Liquid metals exhibit remarkable mechanical properties, in particular large surface tension and low viscosity. However, these properties are greatly affected by oxidation when exposed to air. We measure the viscosity, surface tension, and contact angle of gallium and a eutectic gallium-indium alloy while controlling such oxidation by surrounding the metals with an acid bath of variable concentration. Rheometry measurements reveal a yield stress directly attributable to an oxide skin that obscures the intrinsic behavior of the liquid metals. We demonstrate how the intrinsic viscosity can be obtained with precision through a scaling technique that collapses low- and high-Reynolds number data. Measuring surface tension with a pendant drop method, we show that the oxide skin generates a surface stress that mimics surface tension and develop a simple model to relate this to the yield stress obtained from Rheometry. We find that yield stress, surface tension, and contact angle all transition from solid-like to ...
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effect of oxidation on the mechanical properties of liquid gallium and eutectic gallium indium
arXiv: Fluid Dynamics, 2012Co-Authors: Nikolai Qudalov, Qiti Guo, Heinrich M Jaeger, Eric BrownAbstract:Liquid metals exhibit remarkable mechanical properties, in particular large surface tension and low viscosity. However, these properties are greatly affected by oxidation when exposed to air. We measure the viscosity, surface tension, and contact angle of gallium (Ga) and a eutectic gallium-indium alloy (eGaIn) while controlling such oxidation by surrounding the metal with an acid bath of variable concentration. Rheometry measurements reveal a yield stress directly attributable to an oxide skin that obscures the intrinsic behavior of the liquid metals. We demonstrate how the intrinsic viscosity can be obtained with precision through a scaling technique that collapses low- and high-Reynolds number data. Measuring surface tension with a pendant drop method, we show that the oxide skin generates a surface stress that mimics surface tension and develop a simple model to relate this to the yield stress obtained from Rheometry. We find that yield stress, surface tension, and contact angle all transition from solid-like to liquid behavior at the same critical acid concentration, thereby quantitatively confirming that the wettability of these liquid metals is due to the oxide skin.
