Shear Thickening in Non-Brownian Suspensions: An Excluded Volume Effect

Picano, Francesco; Breugem, Wim-Paul; Mitra, Dhrubaditya; Brandt, Luca

doi:10.1103/physrevlett.111.098302

Cited by 81 publications

(108 citation statements)

References 24 publications

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“…Choosing as reference length the initial radius of the droplets r, the size of the domain is 16r x 16r x 10r (x, y and z, respectively), as sketched in figure 1. This configuration has been widely adopted in literature for the study of rheology of suspensions of rigid and deformable particles and emulsions (see Picano et al 2013;Rosti et al 2019). The flow is governed by four non-dimensional parameters, namely the Reynolds number Re, the capillary number Ca, the viscosity ratio λ and the volume fraction φ, with…”

Section: Flow Configurationmentioning

confidence: 99%

On the effect of coalescence on the rheology of emulsions

et al. 2019

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We present a numerical study of the rheology of a two-fluid emulsion in dilute and semidilute conditions. The analysis is performed for different capillary numbers, volume fraction and viscosity ratio under the assumption of negligible inertia and zero buoyancy force. The effective viscosity of the system increases for low values of the volume fraction and decreases for higher values, with a maximum for about 20% concentration of the disperse phase. When the dispersed fluid has lower viscosity, the normalised effective viscosity becomes smaller than 1 for high enough volume fractions. To single out the effect of droplet coalescence on the rheology of the emulsion we introduce an Eulerian force which prevents merging, effectively modelling the presence of surfactants in the system. When the coalescence is inhibited the effective viscosity is always greater than 1 and the curvature of the function representing the emulsion effective viscosity vs. the volume fraction becomes positive, resembling the behaviour of suspensions of deformable particles. The reduction of the effective viscosity in the presence of coalescence is associated to the reduction of the total surface of the disperse phase when the droplets merge, which leads to a reduction of the interface tension contribution to the total shear stress. The probability density function of the flow topology parameter shows that the flow is mostly a shear flow in the matrix phase, with regions of extensional flow when the coalescence is prohibited. The flow in the disperse phase, instead, always shows rotational components. The first normal stress difference is positive, except for the smallest viscosity ratio considered, whereas the second normal difference is negative, with their ratio being constant with the volume fraction. Our results clearly show that the coalescence efficiency strongly affects the system rheology and neglecting droplet merging can lead to erroneous predictions. † Email address for correspondence: fdv@mech.kth.se

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Section: Flow Configurationmentioning

confidence: 99%

On the effect of coalescence on the rheology of emulsions

et al. 2019

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“…We go beyond direct numerical simulations [19], which are very accurate, but limited in practice to the semi-dilute regime i.e. to suspension viscosities smaller than, say, ten times that of the fluid (Fig.…”

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“…Red △: compilation of data for isodense non-brownian suspensions [23,24]. Green ▽: direct numerical simulations of non-Brownian suspensions [19]. Orange •: compilation of numerical data obtained by Stokesian dynamics [20].…”

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Athermal analogue of sheared dense Brownian suspensions

Trulsson¹,

Bouzid²,

Kurchan³

et al. 2015

EPL

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-The rheology of dense Brownian suspensions of hard spheres is investigated numerically beyond the low shear rate Newtonian regime. We analyze an athermal analogue of these suspensions, with an effective logarithmic repulsive potential representing the vibrational entropic forces. We show that both systems present the same rheology without adjustable parameters. Moreover, all rheological responses display similar Herschel-Bulkley relations once the shear stress and the shear rate are respectively rescaled by a characteristic stress scale and by a microscopic reorganization time-scale, both related to the normal confining pressure. This pressure-controlled approach, originally developed for granular flows, reveals a striking physical analogy between the colloidal glass transition and granular jamming.Amorphous materials [1] such as granular packings [2], colloidal suspensions [3][4][5][6][7] or glassy molecular systems [8-10] display a severe increase in their viscosity before solidifying. With glass-forming liquids, an amorphous solid is obtained by rapidly cooling below the freezing temperature. In the case of systems of hard particles with size dispersion, an emergent solid-like behavior as the packing fraction φ is increased and the amorphous character stems from geometrical disorder. In spite of essential differences in microscopic interactions, the existence of a universal scenario leading to a dynamical slowing down and to the emergence of rigidity [11] remains a vivid issue [10,[12][13][14][15]. Colloids, by the nature of their interparticle interactions and their size, are at the cross-roads between molecular thermal systems and athermal granular materials [16,17,[22][23][24][25][26][27][28][29]. In the dense regime, colloidal suspensions bear all the phenomenological complexity shared by glassforming materials. The strong dynamical slowing down is associated with particle trapping in cages formed by their neighbours [6,30]. Because of this relatively simple picture, colloids are often considered as paradigmatic systems to approach the general issues of dynamical arrest, glass transition and non-Newtonian rheology observed in complex fluids.The overall viscosity of an athermal suspension results from two contributions: the fluid and the particles. (Fig. 1), that there is an increase with particle density in the system's viscosity due to an increase in hydrodynamic interactions. However, this effect does not account for the drastic dynamical slowing-down measured experimentally [22][23][24][25]: even for the state of the art numerical simulations [20,21], the viscosity is strongly underestimated in the dense limit (Fig. 1). As shown in [25], a stress related to collective particle effects and in the complexity of the particle trajectories under geometrical constraints, is actually responsible for the diverging viscosity [26,27].In this letter, we extend this line of thought to dense Brownian suspensions using a model that focusses on collective particle phenomena, the physics at play becoming cl...

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“…Consider a rough surface with a Gaussian height distribution, an expression for the coherent field is I coh ¼ hw sc ihw scÃ i ¼ I 0 expðÀgÞ; (5) where g ¼ k 2 C 2 r 2 , and I 0 is the coherent scattered intensity for a corresponding smooth surface. Consequently, the average diffuse field intensity is calculated using w sc…”

Section: Discussion and Resultsmentioning

confidence: 99%

How shadows shape our impression of rough surfaces

Salami

Hajian

Fazeli

et al. 2014

Journal of Applied Physics

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Articles you may be interested inDrop splashing on a rough surface: How surface morphology affects splashing threshold Appl. Phys. Lett.Shape of a large drop on a rough hydrophobic surface Phys. Fluids 25, 022102 (2013); 10.1063/1.4789494 Examination of coherent surface reflection coefficient (CSRC) approximations in shallow water propagationThe aim here is to shape our impression of rough surfaces based on the formation of shadows. The shadows blackout some parts of the surface leading us to state that rough surfaces are not always quite the way they seem. In fact, it is the angle of view that proves the size of the shadows. In surface profilometry, the scanned image is produced by a vertical shot. While in nature, a vertical sighting of events is not always possible or preferred, therefore readings by various observers would depend on the angle of their line of sight. In the present work, owing to the statistical properties of rough surfaces, the relation between a vertical and angular line of site view of a surface is obtained. This enables the estimation of how the surface really looks like, even though the observer has an non vertical line of sight. To be most illustrative, a comparison between wave scattering from an actual surface and that from an observed surface is performed. The shadowing effects which are shown to be inversely proportional to the Hurst exponent, cause the height correlation function to posses a bi-scaling behaviour. We also illustrate how the correlation develops its efficiency as the line of sight angle tends to zero, making the surface look smooth. V C 2014 AIP Publishing LLC. [http://dx.

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Shear Thickening in Non-Brownian Suspensions: An Excluded Volume Effect

Cited by 81 publications

References 24 publications

On the effect of coalescence on the rheology of emulsions

On the effect of coalescence on the rheology of emulsions

Athermal analogue of sheared dense Brownian suspensions

How shadows shape our impression of rough surfaces

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