Towards rationalising collapse times for the delayed sedimentation of weakly-aggregated colloidal gels

Buscall, Richard; Choudhury, Tahsin H.; Faers, Malcolm A.; Goodwin, James W.; Luckham, P.F.; Partridge, Susan

doi:10.1039/b805807e

Cited by 52 publications

(52 citation statements)

References 17 publications

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“…Indeed, gravity induces both compressive stresses in the bulk of the gel and shear stresses near adhesive vertical walls of its container, 7,8 either of which could cause delayed collapse. Delayed yielding and the difficulties in its prediction is a problem for a wide range of heterogeneous solids, including steel 29 , wood 30 , ceramics 31 and soft solids 9,11 . Although delayed yielding in these materials have somewhat different physical origin on the microscopic level, it originates from the interplay between thermal fluctuations, structure, applied stresses and sometimes corrosion phenomena.…”

Section: Discussionmentioning

confidence: 99%

“…Gravity induces compression in the bulk and shear near adhesive vertical walls. 7,8 Under gravitational load as well as in simple shear, the time delay before yielding decreases exponentially with stress, 3,9 indicating that a stress-dependent energy barrier governs failure at the particle-level. 9 However, this picture is complicated by the strand architecture, which has an order-of-magnitude effect on delay time.…”

Section: Introductionmentioning

confidence: 99%

“…7,8 Under gravitational load as well as in simple shear, the time delay before yielding decreases exponentially with stress, 3,9 indicating that a stress-dependent energy barrier governs failure at the particle-level. 9 However, this picture is complicated by the strand architecture, which has an order-of-magnitude effect on delay time. 10 To achieve predictive capability with a physical model, we must consider the full complexity of the system; this must include the effects of thermal fluctuations and of stresses at all levels of structure.…”

Section: Introductionmentioning

confidence: 99%

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Structures, stresses, and fluctuations in the delayed failure of colloidal gels

et al. 2012

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Sample-spanning networks of aggregated colloidal particles have a finite stiffness and deform elastically when subjected to a small shear stress. After some period of creep, these gels ultimately suffer catastrophic failure. This delayed yielding is governed by the association and dissociation dynamics of interparticle bonds and the strand structure of the gel. We derive a model which connects the kinetics of the colloids to the erosion of the strand structure and ultimately to macroscopic failure. Importantly, this model relates time-to-failure of the gel to an applied static stress. Model predictions are in quantitative agreement with experiments. It is predicted that the strand structure, characterized by its mesh size and strand coarseness, has a significant impact on delay time. Decreasing the mesh size or increasing the strand thickness makes colloidal gels more resilient to delayed yielding. The quench and flow history of gels modify their microstructures. Our experiments show that a slow quenching increases the delay time due to the coarsening of the strands; by contrast, preshear reduces the delay time, which we explain by the increased mesh size as a result of shear-induced fracture of strands.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structures, stresses, and fluctuations in the delayed failure of colloidal gels

et al. 2012

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“…However, they typically yield under a modest stress, often including the gravitational stress exerted by their own weight. It is therefore not surprising that many studies have been devoted to the sedimentation behavior of colloidal gels, revealing a wealth of fascinating but yet not fully understood phenomena, such as delayed sedimentation [4,5,6,7,8], creep [4,9,10,11,12], and fracture associated with complex flow patterns [4,9,13]. With a few notable exceptions [4,6,8], most previous work has focussed on the macroscopic behavior of the gels, typically by measuring the time evolution of the gel height, h(t).…”

Section: Introductionmentioning

confidence: 99%

Equilibrium concentration profiles and sedimentation kinetics of colloidal gels under gravitational stress

Buzzaccaro¹,

Secchi²,

Brambilla³

et al. 2012

J. Phys.: Condens. Matter

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Abstract. We study the sedimentation of colloidal gels by using a combination of light scattering, polarimetry and video imaging. The asymptotic concentration profiles ϕ(z, t → ∞) exhibit remarkable scaling properties: profiles for gels prepared at different initial volume fractions and particle interactions can be superimposed onto a single master curve by using suitable reduced variables. We show theoretically that this behavior stems from a power law dependence of the compressive elastic modulus vs ϕ, which we directly test experimentally. The sedimentation kinetics comprises an initial latency stage, followed by a rapid collapse where the gel height h decreases at constant velocity, and a final compaction stage characterized by a stretched exponential relaxation of h towards a plateau. Analogies and differences with previous works are briefly discussed.

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“…26 To make matters worse, particles are often denser than the surrounding fluid which fosters syneresis and may trigger the collapse of the gel. [27][28][29][30][31] Such density mismatch is further suspected to influ-external shear involves heterogeneous flows that are highly sensitive to preshear history, boundary conditions, and/or finite size effects. For instance, one can emphasize the case of LAPONITE s suspensions whose steady-state flow properties were shown to be influenced by the nature of boundaries: under external shear, smooth walls lead to the complete fluidization of the gel and to linear velocity profiles, while rough boundary conditions allow the growth of a steady shear band.…”

Section: Introductionmentioning

confidence: 99%

Avalanche-like fluidization of a non-Brownian particle gel

et al. 2015

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We report on the fluidization dynamics of an attractive gel composed of non-Brownian particles made of fused silica colloids. Extensive rheology coupled to ultrasonic velocimetry allows us to characterize the global stress response together with the local dynamics of the gel during shear startup experiments.In practice, after being rejuvenated by a preshear, the gel is left to age for a time t w before being subjected to a constant shear rate _ g. We investigate in detail the effects of both t w and _ g on the fluidization dynamics and build a detailed state diagram of the gel response to shear startup flows. The gel may display either transient shear banding towards complete fluidization or steady-state shear banding. In the former case, we unravel that the progressive fluidization occurs by successive steps that appear as peaks on the global stress relaxation signal. Flow imaging reveals that the shear band grows until complete fluidization of the material by sudden avalanche-like events which are distributed heterogeneously along the vorticity direction and correlated to large peaks in the slip velocity at the moving wall. These features are robust over a wide range of t w and _ g values, although the very details of the fluidization scenario vary with _ g. Finally, the critical shear rate _ g* that separates steady-state shear-banding from steady-state homogeneous flow depends on the width of the shear cell and exhibits a nonlinear dependence with t w . Our work brings about valuable experimental data on transient flows of attractive dispersions, highlighting the subtle interplay between shear, wall slip and aging whose modeling constitutes a major challenge that has not been met yet.

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Towards rationalising collapse times for the delayed sedimentation of weakly-aggregated colloidal gels

Cited by 52 publications

References 17 publications

Structures, stresses, and fluctuations in the delayed failure of colloidal gels

Structures, stresses, and fluctuations in the delayed failure of colloidal gels

Equilibrium concentration profiles and sedimentation kinetics of colloidal gels under gravitational stress

Avalanche-like fluidization of a non-Brownian particle gel

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