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R I Tanner - One of the best experts on this subject based on the ideXlab platform.
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oscillatory strain with superposed steady shearing in noncolloidal Suspensions
Journal of Rheology, 2020Co-Authors: Arif Mahmud, Shaocong Dai, R I TannerAbstract:The Rheology of noncolloidal Suspensions in superposed simple shearing and oscillatory shearing was explored. With a Newtonian matrix fluid, one would expect that G′ would be zero in an oscillatory flow, but this was not found; the action of Coulomb friction between the particles appears to cause an increment of G′ at lower frequencies. To understand this frictional effect, measurements of small and medium strain oscillatory flows, up to 10% strain magnitude, were made. The matrix fluid was 12 Pa s silicone oil, and the polystyrene spheres were on average 40.3 μm in diameter. Hysteresis during tests with varying strain amplitudes was more dominant in the storage modulus than in the loss modulus, and, at a 50% volume fraction, the effect was severe. Because of the observed tendency to hysteresis, the oscillatory flow was then combined with a parallel steady shear flow to try to control or eliminate hysteresis. The hysteresis appears to be a frictional effect, and it was reduced under superposed shearing. The effect of variable oscillatory shear stress and steady shear stress was studied, and a model was proposed for the superposed storage modulus, loss modulus, and shear viscosity responses. Frictional effects are considered in the proposed model, and one observes a generally satisfactory fit to the experimental data. From the model, the average friction coefficient is shown to be less at higher frequencies due to higher relative rubbing speeds and better lubrication between the particles. Clearly, Suspension Rheology is dominated by friction and is essentially a study in tribology.
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computation and experiment in non colloidal Suspension Rheology
Journal of Non-newtonian Fluid Mechanics, 2020Co-Authors: R I TannerAbstract:Abstract This paper presents a current view of non-Brownian (non-colloidal) Suspension Rheology; experimental and computational works are compared where possible. The matrix fluids are either Newtonian or viscoelastic; the rigid particles are compact and close to spherical. Volume fractions of 0.5 and below are considered. It is important to move beyond steady simple shearing, so unsteady shearing and uniaxial extensional flows are discussed. Steady shearing is fairly well understood but the extensional flows are not prominent in the literature. In steady shearing with Newtonian matrices the role of friction and the estimation of the average friction coefficient, which reduces as the macroscopic shear stress (or shear rate) increases, is discussed. The ratio of the two normal stress differences to the shear stress is modelled well provided a reasonable value for the average friction coefficient is assumed. With viscoelastic matrices agreement between experiment and theory is less satisfactory. Unsteady and oscillatory flows are surveyed briefly; the prominent hysteresis in oscillatory flows appears to be a frictional effect. While progress has occurred it appears that satisfying agreement between computation and experiment is rare. More attention to rheological and frictional modelling is needed, and improved computational methods may need to be developed.
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shear thickening of a non colloidal Suspension with a viscoelastic matrix
Journal of Fluid Mechanics, 2019Co-Authors: Adolfo Vazquezquesada, R I Tanner, Pep Espanol, Marco ElleroAbstract:We study the Rheology of a non-colloidal Suspension of rigid spherical particles interacting with a viscoelastic matrix. Three-dimensional numerical simulations under shear flow are performed using the smoothed particle hydrodynamics method and compared with experimental data available in the literature using different constant-viscosity elastic Boger fluids. The rheological properties of the Boger matrices are matched in simulation under viscometric flow conditions. Suspension Rheology under dilute to semi-concentrated conditions (i.e. up to solid volume fraction ) is explored. It is found that at small Deborah numbers (based on the macroscopic imposed shear rate), relative Suspension viscosities exhibit a plateau at every concentration investigated. By increasing , shear thickening is observed, which is related to the extensional thickening of the underlying viscoelastic matrix. Under dilute conditions ( ), numerical results for agree quantitatively with experimental data in both the and dependences. Even under dilute conditions, simulations of full many-particle systems with no a priori specification of their spatial distribution need to be considered to recover precisely experimental values. By increasing the solid volume fraction towards , despite the fact that the trend is well captured, the agreement remains qualitative with discrepancies arising in the absolute values of obtained from simulations and experiments but also with large deviations existing among different experiments. With regard to the specific mechanism of elastic thickening, the microstructural analysis shows that elastic thickening correlates well with the average viscoelastic dissipation function , requiring a scaling as with to take place. Locally, despite the fact that regions of large polymer stretching (and viscoelastic dissipation) can occur everywhere in the domain, flow regions uniquely responsible for the elastic thickening are well correlated to areas with significant extensional component.
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review article aspects of non colloidal Suspension Rheology
Physics of Fluids, 2018Co-Authors: R I TannerAbstract:This review deals with non-Brownian (non-colloidal) Suspension Rheology; experimental and computational studies are compared where possible. The matrix fluids are Newtonian, and the rigid particles have an aspect ratio close to one. Volume fractions up to and including 0.5 are considered. Shearing and extensional flows are discussed; the former are fairly well understood, but the latter are not prominent in the literature. Unsteady and oscillatory flows are surveyed; more work is needed in this area. Finally some attempts to find constitutive models are discussed, and an empirically based suggestion based on a modified Reiner-Rivlin model is described.This review deals with non-Brownian (non-colloidal) Suspension Rheology; experimental and computational studies are compared where possible. The matrix fluids are Newtonian, and the rigid particles have an aspect ratio close to one. Volume fractions up to and including 0.5 are considered. Shearing and extensional flows are discussed; the former are fairly well understood, but the latter are not prominent in the literature. Unsteady and oscillatory flows are surveyed; more work is needed in this area. Finally some attempts to find constitutive models are discussed, and an empirically based suggestion based on a modified Reiner-Rivlin model is described.
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review article aspects of non colloidal Suspension Rheology
Physics of Fluids, 2018Co-Authors: R I TannerAbstract:This review deals with non-Brownian (non-colloidal) Suspension Rheology; experimental and computational studies are compared where possible. The matrix fluids are Newtonian, and the rigid particles have an aspect ratio close to one. Volume fractions up to and including 0.5 are considered. Shearing and extensional flows are discussed; the former are fairly well understood, but the latter are not prominent in the literature. Unsteady and oscillatory flows are surveyed; more work is needed in this area. Finally some attempts to find constitutive models are discussed, and an empirically based suggestion based on a modified Reiner-Rivlin model is described.
Takuji Ishikawa - One of the best experts on this subject based on the ideXlab platform.
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Rheology of a dilute Suspension of deformable microswimmers
Physics of Fluids, 2020Co-Authors: Hitomu Matsui, Toshihiro Omori, Takuji IshikawaAbstract:Suspensions of swimming microorganisms play important roles in biology, medicine, and engineering. To predict and control the flow field of such Suspensions, an understanding of their rheological properties is required. In this background, the Suspension Rheology of various types of microorganisms has been investigated intensively. Research has shown that some microorganisms, such as ciliates, deform when a strong force is exerted on their bodies. However, the effect of cell deformability on Suspension Rheology has not yet been clarified. In this study, we used a deformable torque swimmer, as a model ciliate, to investigate the rheological properties of a dilute Suspension under shear flow. Our results show that the model swimmer tends to gradually change its orientation toward the shear plane or vorticity axis. Regardless of the swimming mode, the apparent shear viscosity shows shear-thinning properties, with the first normal stress difference being positive in sign. The second normal stress difference can be positive or negative, depending on the swimming mode, the deformability, and the shear rate. The mechanism to show such rheological properties can be understood based on the deformed shape and direction of the swimmer’s stresslet. These findings are important for understanding the Suspension Rheology of natural microorganisms and artificial deformable swimmers, which is essential to predict and control the flow of these Suspensions.
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Rheology of a dense Suspension of spherical capsules under simple shear flow
Journal of Fluid Mechanics, 2016Co-Authors: Daiki Matsunaga, Takami Yamaguchi, Yohsuke Imai, Takuji IshikawaAbstract:We present a numerical analysis of the Rheology of a dense Suspension of spherical capsules in simple shear flow in the Stokes flow regime. The behaviour of neo-Hookean capsules is simulated for a volume fraction up to ${\it\phi}=0.4$ by graphics processing unit computing based on the boundary element method with a multipole expansion. To describe the specific viscosity using a polynomial equation of the volume fraction, the coefficients of the equation are calculated by least-squares fitting. The results suggest that the effect of higher-order terms is much smaller for capsule Suspensions than rigid sphere Suspensions; for example, $O({\it\phi}^{3})$ terms account for only 8 % of the specific viscosity even at ${\it\phi}=0.4$ for capillary numbers $Ca\geqslant 0.1$ . We also investigate the relationship between the deformation and orientation of the capsules and the Suspension Rheology. When the volume fraction increases, the deformation of the capsules increases while the orientation angle of the capsules with respect to the flow direction decreases. Therefore, both the specific viscosity and the normal stress difference increase with volume fraction due to the increased deformation, whereas the decreased orientation angle suppresses the specific viscosity, but amplifies the normal stress difference.
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Rheology of a dense Suspension of spherical capsules under simple shear flow
Journal of Fluid Mechanics, 2016Co-Authors: Daiki Matsunaga, Takami Yamaguchi, Yohsuke Imai, Takuji IshikawaAbstract:We present a numerical analysis of the Rheology of a dense Suspension of spherical capsules in simple shear flow in the Stokes flow regime. The behaviour of neo-Hookean capsules is simulated for a volume fraction up to by graphics processing unit computing based on the boundary element method with a multipole expansion. To describe the specific viscosity using a polynomial equation of the volume fraction, the coefficients of the equation are calculated by least-squares fitting. The results suggest that the effect of higher-order terms is much smaller for capsule Suspensions than rigid sphere Suspensions; for example, terms account for only 8 % of the specific viscosity even at for capillary numbers . We also investigate the relationship between the deformation and orientation of the capsules and the Suspension Rheology. When the volume fraction increases, the deformation of the capsules increases while the orientation angle of the capsules with respect to the flow direction decreases. Therefore, both the specific viscosity and the normal stress difference increase with volume fraction due to the increased deformation, whereas the decreased orientation angle suppresses the specific viscosity, but amplifies the normal stress difference.
Matthias Fuchs - One of the best experts on this subject based on the ideXlab platform.
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first principles constitutive equation for Suspension Rheology
Physical Review E, 2012Co-Authors: Joseph M Brader, Michael E. Cates, Matthias FuchsAbstract:The imposition of flow can drive a fluid far from equilibrium. Because of the occurrence of long relaxation times, this effect is ubiquitous in complex fluids (colloids, polymers, etc.) whose Rheology is of significant technological interest, and also represents an important challenge in nonequilibrium statistical physics. Continuum approaches have provided important insights, using symmetry and other principles to construct or constrain phenomenological constitutive relations. While the constitutive equations of Newtonian fluids and Hookian solids are derivable from fundamental starting points (the theory of linear response based on Onsager’s regression hypothesis), there has been less progress with their nonlinear generalizations for viscoelastic fluids, plastic solids and other strongly deforming soft materials. A central aim of theoretical Rheology is thus to derive from the underlying microscopic interactions the constitutive equations that relate the stress tensor to the macroscopic deformation history of a material. For entangled polymer melts, the constitutive equation of Doi and Edwards [1] has enjoyed considerable success. An analogously general microscopic constitutive equation for colloidal dispersions remains conspicuously lacking [2]. Even the simplest hard-sphere colloids in concentrated Suspension exhibit a broad range of viscoelastic behavior; alongside to flow-thinning [3] and thickening [4], slow structural relaxation leads to glasses showing a solidlike response, strain hardening or softening, and plastic flow [5]. But, while the linear viscoelastic spectra of colloidal Suspensions are fairly well understood [6], only recently has progress been made in nonlinear flow predictions for simple shear [7,8]. Shear represents a relatively weak flow in which material lines grow linearly with time, while in elongational flows such growth is exponential, creating much more severe deformations of material elements. Thus, a description capable of handling arbitrary deformation histories is highly desirable. In the continuum approaches, invariance arguments strongly restrict the
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first principles constitutive equation for Suspension Rheology
Physical Review Letters, 2008Co-Authors: Joseph M Brader, Michael E. Cates, Matthias FuchsAbstract:Using mode-coupling theory, we derive a constitutive equation for the nonlinear Rheology of dense colloidal Suspensions under arbitrary time-dependent homogeneous flow. Generalizing previous results for simple shear, this allows the full tensorial structure of the theory to be identified. Macroscopic deformation measures, such as the Cauchy-Green tensors, thereby emerge. So does a direct relation between the stress and the distorted microstructure, illuminating the interplay of slow structural relaxation and arbitrary imposed flow. We present flow curves for steady planar and uniaxial elongation and compare these to simple shear. The resulting nonlinear Trouton ratios point to a tensorially nontrivial dynamic yield condition for colloidal glasses.
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Glass transitions and shear thickening Suspension Rheology
Journal of Rheology, 2005Co-Authors: C. B. Holmes, Michael E. Cates, Matthias Fuchs, Peter SollichAbstract:We introduce a class of simple models for shear thickening and/or “jamming” in colloidal Suspensions. These are based on the schematic mode coupling theory (MCT) of the glass transition, having a memory term that depends on a density variable, and on both the shear stress and the shear rate. (Tensorial aspects of the Rheology, such as normal stresses, are ignored for simplicity.) We calculate steady-state flow curves and correlation functions. Depending on model parameters, we find a range of rheological behaviors, including “S-shaped” flow curves, indicating discontinuous shear thickening, and stress-induced transitions from a fluid to a nonergodic (jammed) state, showing zero flow rate in an interval of applied stress. The shear thickening and jamming scenarios that we explore appear broadly consistent with experiments on dense colloids close to the glass transition, despite the fact that we ignore hydrodynamic interactions. In particular, the jamming transition we propose is conceptually quite differen...
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glass transitions and shear thickening Suspension Rheology
arXiv: Soft Condensed Matter, 2004Co-Authors: C. B. Holmes, Matthias Fuchs, M E Cates, Peter SollichAbstract:We introduce a class of simple models for shear thickening and/ or `jamming' in colloidal Suspensions. These are based on schematic mode coupling theory (MCT) of the glass transition, having a memory term that depends on a density variable, and on both the shear stress and the shear rate. (Tensorial aspects of the Rheology, such as normal stresses, are ignored for simplicity.) We calculate steady-state flow curves and correlation functions. Depending on model parameters, we find a range of rheological behaviours, including `S-shaped' flow curves, indicating discontinuous shear thickening, and stress-induced transitions from a fluid to a nonergodic (jammed) state, showing zero flow rate in an interval of applied stress. The shear thickening and jamming scenarios that we explore appear broadly consistent with experiments on dense colloids close to the glass transition, despite the fact that we ignore hydrodynamic interactions. In particular, the jamming transition we propose is conceptually quite different from various hydrodynamic mechanisms of shear thickening in the literature, although the latter might remain pertinent at lower colloid densities. Our jammed state is a stress-induced glass, but its nonergodicity transitions have an analytical structure distinct from that of the conventional MCT glass transition.
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jamming transitions in a schematic model of Suspension Rheology
arXiv: Soft Condensed Matter, 2002Co-Authors: C. B. Holmes, Matthias Fuchs, M E CatesAbstract:We study the steady-state response to applied stress in a simple scalar model of sheared colloids. Our model is based on a schematic (F2) model of the glass transition, with a memory term that depends on both stress and shear rate. For suitable parameters, we find transitions from a fluid to a nonergodic, jammed state, showing zero flow rate in an interval of applied stress. Although the jammed state is a glass, we predict that jamming transitions have an analytical structure distinct from that of the conventional mode coupling glass transition. The static jamming transition we discuss is also distinct from hydrodynamic shear thickening.
Michael E. Cates - One of the best experts on this subject based on the ideXlab platform.
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first principles constitutive equation for Suspension Rheology
Physical Review E, 2012Co-Authors: Joseph M Brader, Michael E. Cates, Matthias FuchsAbstract:The imposition of flow can drive a fluid far from equilibrium. Because of the occurrence of long relaxation times, this effect is ubiquitous in complex fluids (colloids, polymers, etc.) whose Rheology is of significant technological interest, and also represents an important challenge in nonequilibrium statistical physics. Continuum approaches have provided important insights, using symmetry and other principles to construct or constrain phenomenological constitutive relations. While the constitutive equations of Newtonian fluids and Hookian solids are derivable from fundamental starting points (the theory of linear response based on Onsager’s regression hypothesis), there has been less progress with their nonlinear generalizations for viscoelastic fluids, plastic solids and other strongly deforming soft materials. A central aim of theoretical Rheology is thus to derive from the underlying microscopic interactions the constitutive equations that relate the stress tensor to the macroscopic deformation history of a material. For entangled polymer melts, the constitutive equation of Doi and Edwards [1] has enjoyed considerable success. An analogously general microscopic constitutive equation for colloidal dispersions remains conspicuously lacking [2]. Even the simplest hard-sphere colloids in concentrated Suspension exhibit a broad range of viscoelastic behavior; alongside to flow-thinning [3] and thickening [4], slow structural relaxation leads to glasses showing a solidlike response, strain hardening or softening, and plastic flow [5]. But, while the linear viscoelastic spectra of colloidal Suspensions are fairly well understood [6], only recently has progress been made in nonlinear flow predictions for simple shear [7,8]. Shear represents a relatively weak flow in which material lines grow linearly with time, while in elongational flows such growth is exponential, creating much more severe deformations of material elements. Thus, a description capable of handling arbitrary deformation histories is highly desirable. In the continuum approaches, invariance arguments strongly restrict the
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first principles constitutive equation for Suspension Rheology
Physical Review Letters, 2008Co-Authors: Joseph M Brader, Michael E. Cates, Matthias FuchsAbstract:Using mode-coupling theory, we derive a constitutive equation for the nonlinear Rheology of dense colloidal Suspensions under arbitrary time-dependent homogeneous flow. Generalizing previous results for simple shear, this allows the full tensorial structure of the theory to be identified. Macroscopic deformation measures, such as the Cauchy-Green tensors, thereby emerge. So does a direct relation between the stress and the distorted microstructure, illuminating the interplay of slow structural relaxation and arbitrary imposed flow. We present flow curves for steady planar and uniaxial elongation and compare these to simple shear. The resulting nonlinear Trouton ratios point to a tensorially nontrivial dynamic yield condition for colloidal glasses.
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Glass transitions and shear thickening Suspension Rheology
Journal of Rheology, 2005Co-Authors: C. B. Holmes, Michael E. Cates, Matthias Fuchs, Peter SollichAbstract:We introduce a class of simple models for shear thickening and/or “jamming” in colloidal Suspensions. These are based on the schematic mode coupling theory (MCT) of the glass transition, having a memory term that depends on a density variable, and on both the shear stress and the shear rate. (Tensorial aspects of the Rheology, such as normal stresses, are ignored for simplicity.) We calculate steady-state flow curves and correlation functions. Depending on model parameters, we find a range of rheological behaviors, including “S-shaped” flow curves, indicating discontinuous shear thickening, and stress-induced transitions from a fluid to a nonergodic (jammed) state, showing zero flow rate in an interval of applied stress. The shear thickening and jamming scenarios that we explore appear broadly consistent with experiments on dense colloids close to the glass transition, despite the fact that we ignore hydrodynamic interactions. In particular, the jamming transition we propose is conceptually quite differen...
Jacob I Emert - One of the best experts on this subject based on the ideXlab platform.
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effect of temperature on carbon black agglomeration in hydrocarbon liquid with adsorbed dispersant
Langmuir, 2005Co-Authors: Steve P Meeker, Volker Trappe, Nancy Z Diggs, David A Weitz, Jacob I EmertAbstract:Suspensions of carbon black in oil, stabilized with adsorbed polyisobutylene succinimide (PIBSI) dispersant, are commonly used as model systems for investigating the soot-handling characteristics of motor oils. The structure of the carbon-black agglomerates changes dramatically with temperature; this results in a concomitant change in the Suspension Rheology. Linear and nonlinear rheological experiments indicate a large increase of the interparticle attractions as the temperature is raised. To elucidate the origin of this behavior, we investigate the effect of temperature on the stabilizing effect of the dispersant. Measurements of adsorption isotherms of the dispersant on carbon black indicate that there is little variation of the binding energy with temperature. Intrinsic viscosity measurements of PIBSI dispersants in solution clearly exhibit an inverse dependence of the dispersant chain dimension with temperature. These results suggest that the temperature-dependent changes in the chain conformation of...
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effect of temperature on carbon black agglomeration in hydrocarbon liquid with adsorbed dispersant
Langmuir, 2005Co-Authors: Youyeon Won, Steve P Meeker, Volker Trappe, Nancy Z Diggs, David A Weitz, Jacob I EmertAbstract:Suspensions of carbon black in oil, stabilized with adsorbed polyisobutylene succinimide (PIBSI) dispersant, are commonly used as model systems for investigating the soot-handling characteristics of motor oils. The structure of the carbon-black agglomerates changes dramatically with temperature; this results in a concomitant change in the Suspension Rheology. Linear and nonlinear rheological experiments indicate a large increase of the interparticle attractions as the temperature is raised. To elucidate the origin of this behavior, we investigate the effect of temperature on the stabilizing effect of the dispersant. Measurements of adsorption isotherms of the dispersant on carbon black indicate that there is little variation of the binding energy with temperature. Intrinsic viscosity measurements of PIBSI dispersants in solution clearly exhibit an inverse dependence of the dispersant chain dimension with temperature. These results suggest that the temperature-dependent changes in the chain conformation of the PIBSI dispersant are primarily responsible for the changes in the dispersion Rheology, and we propose a simple model to account for these data.
