Rheology of Confined Non-Brownian Suspensions

Fornari, Walter; Brandt, Luca; Chaudhuri, Pinaki; Lopez, Cyan Umbert; Mitra, Dhrubaditya; Picano, Francesco

doi:10.1103/physrevlett.116.018301

Cited by 37 publications

(36 citation statements)

References 30 publications

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“…The effect of the size of the domain on the results (e.g., confinement effects) has not been studied in the present work, and the domain size was chosen the same as in a previous study [18]; the interested reader is referred to Ref. [44] for more details on confined suspensions in a similar geometry. Note that, similarly to the box size, also the general set-up and most of parameters used in this study are chosen as in Ref.…”

Section: Numerical Setupmentioning

confidence: 99%

Suspensions of deformable particles in a Couette flow

Rosti

Brandt

2018

Journal of Non-Newtonian Fluid Mechanics

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We consider suspensions of deformable particles in a Newtonian fluid by means of fully Eulerian numerical simulations with a one-continuum formulation. We study the rheology of the visco-elastic suspension in plane Couette flow in the limit of vanishing inertia and examine the dependency of the effective viscosity µ on the solid volume-fraction Φ, the capillary number Ca, and the solid to fluid viscosity ratio K. The suspension viscosity decreases with deformation and applied shear (shear-thinning) while still increasing with volume fraction. We show that µ collapses to an universal function, µ (Φ e ), with an effective volume fraction Φ e , lower than the nominal one owing to the particle deformation. This universal function is well described by the Eilers fit, which well approximate the rheology of suspension of rigid spheres at all Φ. We provide a closure for the effective volume fraction Φ e as function of volume fraction Φ and capillary number Ca and demonstrate it also applies to data in literature for suspensions of capsules and red-blood cells. In addition, we show that the normal stress differences exhibit a non-linear behavior, with a similar trend as in polymer and filament suspensions. The total stress budgets reveals that the particle-induced stress contribution increases with the volume fraction Φ and decreases with deformability.

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Section: Numerical Setupmentioning

confidence: 99%

Suspensions of deformable particles in a Couette flow

Rosti

Brandt

2018

Journal of Non-Newtonian Fluid Mechanics

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“…Recent examples include density excitations (determining frictional properties) in driven colloidal monolayers [1][2][3][4], the stick-slip motion involved in the transmission of torque in driven colloidal clutches [5], as well as heterogeneities [6][7][8][9], and diverging stress-and strain correlations [6,10] in sheared colloidal glasses. Related complex microscopic behavior occurs in sheared granular matter [11] and sheared suspensions of non-Brownian particles [12]. Developing a microscopic understanding of such shear-induced behavior is interesting not only in the general context of nonequilibrium behavior of soft-matter systems, but also is crucial for applications in nanotribology, the design of novel materials and of efficient nanomachines.…”

Section: Introductionmentioning

confidence: 99%

Depinning and heterogeneous dynamics of colloidal crystal layers under shear flow

Gerloff¹,

Klapp²

2016

Phys. Rev. E

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Using Brownian dynamics (BD) simulations and an analytical approach we investigate the shearinduced, nonequilibrium dynamics of dense colloidal suspensions confined to a narrow slit-pore. Focusing on situations where the colloids arrange in well-defined layers with solidlike in-plane structure, the confined films display complex, nonlinear behavior such as collective depinning and local transport via density excitations. These phenomena are reminiscent of colloidal monolayers driven over a periodic substrate potential. In order to deepen this connection, we present an effective model which maps the dynamics of the shear-driven colloidal layers to the motion of a single particle driven over an effective substrate potential. This model allows to estimate the critical shear rate of the depinning transition based on the equilibrium configuration, revealing the impact of important parameters such as the slit-pore width and the interaction strength. We then turn to heterogeneous systems where a layer of small colloids is sheared with respect to bottom layers of large particles. For these incommensurate systems we find that the particle transport is dominated by density excitations resembling the so-called "kink" solutions of the Frenkel-Kontorova (FK) model. In contrast to the FK model, however, the corresponding "antikinks" do not move.

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“…We have checked that doubling the resolution in all directions results in an insignificant (less than 0.5%) change in the results. Also, the size of the domain has been chosen sufficiently large to avoid confinement effects [8,22]. The list of parameters investigated are given in the caption of Fig.…”

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Rheology of suspensions of viscoelastic spheres: Deformability as an effective volume fraction

2018

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We study suspensions of deformable (viscoelastic) spheres in a Newtonian solvent in plane Couette geometry, by means of direct numerical simulations. We find that in the limit of vanishing inertia the effective viscosity µ of the suspension increases as the volume-fraction occupied by the spheres Φ increases and decreases as the elastic modulus of the spheres G decreases; the function µ(Φ, G) collapses to an universal function, µ(Φe), with a reduced effective volume fraction Φe(Φ, G). Remarkably, the function µ(Φe) is the well-known Eilers fit that describes the rheology of suspension of rigid spheres at all Φ. Our results suggest new ways to interpret macro-rheology of blood.Most of the fluids we encounter in our everyday lifefrom the mud we wade through to the blood that flows through our veins -are complex fluids. One of the most useful ways to understand the rheology of complex fluids is to model them as suspensions of objects in a Newtonian solvent with dynamic viscosity µ f and density ρ f [1,2]. The rheology of suspensions can be quite complex, as it depends on the shear-rateγ, the volume-fraction Φ occupied by the suspended objects, the properties of the suspended objects themselves (some examples are rigid spheres, bubbles, a different fluid enclosed in a membrane), and their poly-dispersity. In the simplest case of rigid spheres in the limit of small Φ, and vanishing inertia (smallγ), also ignoring thermal fluctuations (infinite Peclet number), the fractional increase in the effective viscosity of the suspension is given by [see, e.g., 3, section 4.11]At present there is no theory that allows us to calculate µ for any given Φ andγ. Different empirical formulas provide a good description to the existing experimental and numerical results [4][5][6][7]. Among those, we consider here the Eilers formula [1,2],which fits well the experimental and numerical data [5,6] for both low and high values of Φ, up to about 0.6. In the expression above, Φ m is the geometrical maximum packing fraction, and B is a constant, and the best fit to the data yields Φ m = 0.58 − 0.63 and B = 1.25 − 1.7.If the radius R of the spheres and the shear-rate are large enough, the particle Reynolds number, defined as Re ≡ (ρ f R 2γ )/µ f , is greater than unity, inertial effects are non negligible and the viscosity µ = µ(Φ, Re). Remarkably, direct numerical simulations (DNS) in Ref. [8] demonstrated that the Eilers fit is a good approximation even for inertial suspensions if Φ in Eq.(2) is replaced by an increased effective volume fraction, Φ e (Φ, Re). Due to the increase of the effective volume fraction with the applied shear, the suspension viscosity increases, a phenomenon called inertial shear-thickening.In this letter we add a different complexity to this problem, one that is particularly important to understand rheology of biological flows; while keeping small Re, we allow the suspended particles to be deformable.In particular, we model the spheres as viscoelastic material with an elastic shear-modulus G and viscosity µ s . There...

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Rheology of Confined Non-Brownian Suspensions

Cited by 37 publications

References 30 publications

Suspensions of deformable particles in a Couette flow

Suspensions of deformable particles in a Couette flow

Depinning and heterogeneous dynamics of colloidal crystal layers under shear flow

Rheology of suspensions of viscoelastic spheres: Deformability as an effective volume fraction

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