arXiv subjects

Sebastien Manneville

Publications and source records attributed to Sebastien Manneville.

At least 19 recordsLinked to original sources

arXiv2024

Wall slip and bulk flow heterogeneity in a sludge under shear

We investigate the shear flow of a sludge mimicking slurries produced by the nuclear industry and constituted of a dispersion of non-Brownian particles into an attractive colloidal dispersion at a total solid volume fraction of about 10%. Combining rheometry and ultrasound flow imaging, we show that, upon decreasing the shear rate, the flow transitions from a homogeneous shear profile in the bulk to a fully arrested plug-like state with total wall slip, through an oscillatory regime where strong fluctuations of the slip velocity propagate along the vorticity direction. When the shear stress is imposed close to the yield stress, the shear rate presents large, quasi-periodic peaks, associated with the propagation of local stick-and-slip events along the vorticity direction. Such complex dynamics, reminiscent of similar phenomena reported in much denser suspensions, highlight the importance of local flow characterization to fully understand sludge rheology.

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arXiv2024

Critical-like gelation dynamics in cellulose nanocrystal suspensions

We use time-resolved mechanical spectroscopy to offer a detailed picture of the gelation dynamics of cellulose nanocrystal (CNC) suspensions following shear cessation in the presence of salt. CNCs are charged, rodlike colloids that self-assemble into various phases, including physical gels serving as soft precursors for biosourced composites. Here, a series of linear viscoelastic spectra acquired across the sol-gel transition of CNC suspensions are rescaled onto two master curves, that correspond to a viscoelastic liquid state prior to gelation and to a soft solid state after gelation. These two states are separated by a critical gel point, where all rescaling parameters diverge in an asymmetric fashion, yet with exponents that obey hyperscaling relations consistent with previous works on isotropic colloids and polymer gels. Upon varying the salt content, we further show that these critical-like dynamics result in both time-connectivity and time-concentration superposition principles.

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arXiv2022

Slow dynamics and time-composition superposition in gels of cellulose nanocrystals

Cellulose nanocrystals (CNCs) are rodlike biosourced colloidal particles used as key building blocks in a growing number of materials with innovative mechanical or optical properties. While CNCs form stable suspensions at low volume fractions in pure water, they aggregate in the presence of salt and form colloidal gels with time-dependent properties. Here, we study the impact of salt concentration on the slow aging dynamics of CNC gels following the cessation of a high-shear flow that fully fluidizes the sample. We show that the higher the salt content, the faster the recovery of elasticity upon flow cessation. Most remarkably, the elastic modulus $G'$ obeys a time-composition superposition principle: the temporal evolution of $G'$ can be rescaled onto a universal sigmoidal master curve spanning 13 orders of magnitude in time for a wide range of salt concentrations. Such a rescaling is obtained through a time-shift factor that follows a steep power-law decay with increasing salt concentration, until it saturates at large salt content. These findings are robust to changes in the type of salt and in the CNC content. We further show that both linear and nonlinear rheological properties of CNC gels of various compositions, including, e.g., the frequency-dependence of viscoelastic spectra and the yield strain, can be rescaled based on the sample age along the general master curve. Our results provide strong evidence for universality in the aging dynamics of CNC gels, and call for microstructural investigations during recovery as well as theoretical modelling of time-composition superposition in rodlike colloids.

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arXiv2021

Interplay between wall slip and shear banding in a thixotropic yield stress fluid

We study the local dynamics of a thixotropic yield stress fluid that shows a pronounced non-monotonic flow curve. This mechanically unstable behavior is generally not observable from standard rheometry tests, resulting in a stress plateau that stems from the coexistence of a flowing band with an unyielded region below a critical shear rate $\dot \gamma_c$. Combining ultrasound velocimetry with standard rheometry, we discover an original shear-banding scenario in the decreasing branch of the flow curve of model paraffin gels, in which the flow profile of the flowing band is set by the applied shear rate $\gd$ instead of $\dot \gamma_c$. As a consequence, the material slips at the walls with a velocity that shows a non-trivial dependence on the applied shear rate. To capture our observations, we propose a differential version of the so-called lever rule, describing the extent of the flowing band and the evolution of wall slip with shear rate. This phenomenological model holds down to very low shear rates, at which the dimension of the flowing band becomes comparable to the size of the wax particles that constitute the gel microstructure, leading to cooperative effects. Our approach provides a framework where constraints imposed in the classical shear-banding scenario can be relaxed, with wall slip acting as an additional degree of freedom.

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arXiv2017

Predicting and assessing rupture in protein gels under oscillatory shear

Soft materials may break irreversibly upon applying sufficiently large shear oscillations, a process which physical mechanism remains largely elusive. In this work, the rupture of protein gels made of sodium caseinate under an oscillatory stress is shown to occur in an abrupt, brittle-like manner. Upon increasing the stress amplitude, the build-up of harmonic modes in the strain response can be rescaled for all gel concentrations. This rescaling yields an empirical criterion to predict the rupture point way before the samples are significantly damaged. "Fatigue" experiments under stress oscillations of constant amplitude can be mapped onto the former results, which indicates that rupture is independent of the temporal pathway in which strain and damage accumulate. Finally, using ultrasonic imaging, we measure the local mechanical properties of the gels before, during and after breakdown, showing that the strain field remains perfectly homogeneous up to rupture but suddenly gives way to a solid-fluid phase separation upon breakdown.

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arXiv2016

Power-law creep and residual stresses in a carbopol microgel

We report on the interplay between creep and residual stresses in a carbopol microgel. When a constant shear stress $σ$ is applied below the yield stress $σ_\text{y}$, the strain is shown to increase as a power law of time, $γ(t)=γ_0 + (t/τ)^α$, with an exponent $α=0.39\pm 0.04$ that is strongly reminiscent of Andrade creep in hard solids. For applied shear stresses lower than some typical value $σ_\text{c}\simeq 0.2 σ_\text{y}$, the microgel experiences a more complex, anomalous creep behaviour, characterized by an initial decrease of the strain, that we attribute to the existence of residual stresses of the order of $σ_\text{c}$ that persist after a rest time under a zero shear rate following preshear. The influence of gel concentration on creep and residual stresses are investigated as well as possible aging effects. We discuss our results in light of previous works on colloidal glasses and other soft glassy systems.

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arXiv2016

Grains unchained: local fluidization of a granular packing by focused ultrasound

We report experimental results on the dynamics of a granular packing submitted to high-intensity focused ultrasound. Acoustic radiation pressure is shown to remotely induce local rearrangements within a pile as well as global motion around the focal spot in an initially jammed system. We demonstrate that this fluidization process is intermittent for a range of acoustic pressures and hysteretic when the pressure is cycled. Such a first-order-like unjamming transition is reproduced in numerical simulations in which the acoustic pressure field is modeled by a localized external force. Further analysis of the simulated packings suggests that in the intermittent regime unjamming is not associated with any noticeable prior structural signature. A simple two-state model based on effective temperatures is proposed to account for these findings.

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arXiv2015

Multiple yielding processes in a colloidal gel under large amplitude oscillatory stress

Fatigue refers to the changes in material properties caused by repeatedly applied loads. It has been widely studied for, e.g., construction materials, but much less has been done on soft materials. Here, we characterize the fatigue dynamics of a colloidal gel. Fatigue is induced by large amplitude oscillatory stress (LAOStress), and the local displacements of the gel are measured through high-frequency ultrasonic imaging. We show that fatigue eventually leads to rupture and fluidization. We evidence four successive steps associated with these dynamics: (i) the gel first remains solid, (ii) it then slides against the walls, (iii) the bulk of the sample becomes heterogeneous and displays solid-fluid coexistence, and (iv) it is finally fully fluidized. It is possible to homogeneously scale the duration of each step with respect to the stress oscillation amplitude $σ_0$. The data are compatible with both exponential and power-law scalings with $σ_0$, which hints at two possible interpretations in terms of delayed yielding in terms activated processes or of the Basquin law. Surprisingly, we find that the model parameters behave nonmonotonically as we change the oscillation frequency and/or the gel concentration.

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arXiv2014

Time dependence in large amplitude oscillatory shear: a rheo-ultrasonic study of fatigue dynamics in a colloidal gel

We report on the response of a yield stress material, namely a colloidal gel made of attractive carbon black particles, submitted to large amplitude oscillatory shear stress (LAOStress). At a constant stress amplitude well below its apparent yield stress, the gel displays fatigue and progressively turns from an elastic solid to a viscous fluid. The time-resolved analysis of the strain response, of the Fourier spectrum, and of Lissajous plots allows one to define two different timescales $τ_w<τ_f$ associated with the yielding and fluidization of the gel. Coupling rheology to ultrasonic imaging further leads to a local picture of the LAOStress response in which the gel first fails at the walls at $τ_w$ and then undergoes a slow heterogeneous fluidization involving solid--fluid coexistence until the whole sample is fluid at $τ_f$. Spatial heterogeneities are observed in both the gradient and vorticity directions and suggest a fragmentation of the initially solidlike gel into macroscopic domains eroded by the surrounding fluidized suspension.

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arXiv2013

Inertio-elastic instability of non shear-banding wormlike micelles

Homogeneous polymer solutions are well-known to exhibit viscoelastic flow instabilities: purely elastic when inertia is negligible, inertio-elastic otherwise. Recently, shear-banding wormlike micelles solutions were also discovered to follow a similar phenomenology. In the shear-banding regime, inertia is usually negligible so only purely elastic flows have been reported. Here, we investigate a non-shear-banding solution where inertia becomes significant, leading to flow patterns akin to the inertio-elastic regime of dilute polymer solutions. We show that the instability follows a supercritical bifurcation and we investigate the structure of the inertio-elastic vortices that develop above onset.

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arXiv2013

Shear-induced structures versus flow instabilities

The Taylor-Couette flow of a dilute micellar system known to generate shear-induced structures is investigated through simultaneous rheometry and ultrasonic imaging. We show that flow instabilities must be taken into account since both the Reynolds number and the Weissenberg number may be large. Before nucleation of shear-induced structures, the flow can be inertially unstable, but once shear-induced structures are nucleated the kinematics of the flow become chaotic, in a pattern reminiscent of the inertio-elastic turbulence known in dilute polymer solutions. We outline a general framework for the interplay between flow instabilities and flow-induced structures.

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arXiv2013

Surfactant micelles: model systems for flow instabilities of complex fluids

Complex fluids such as emulsions, colloidal gels, polymer or surfactant solutions are all characterized by the existence of a "microstructure" which may couple to an external flow on timescales that are easily probed in experiments. Such a coupling between flow and microstructure usually leads to instabilities under relatively weak shear flows that correspond to vanishingly small Reynolds numbers. Wormlike micellar surfactant solutions appear as model systems to study two examples of such instabilities, namely shear banding and elastic instabilities. Focusing on a semidilute sample we show that two dimensional ultrafast ultrasonic imaging allows for a thorough investigation of unstable shear-banded micellar flows. In steady state, radial and azimuthal velocity components are recovered and unveil the original structure of the vortical flow within an elastically unstable high shear rate band. Furthermore thanks to an unprecedented frame rate of up to 20,000 fps, transients and fast dynamics can be resolved, which paves the way for a better understanding of elastic turbulence.

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arXiv2013

Ultrafast ultrasonic imaging coupled to rheometry: principle and illustration

We describe a technique coupling standard rheology and ultrasonic imaging with promising applications to characterization of soft materials under shear. Plane wave imaging using an ultrafast scanner allows to follow the local dynamics of fluids sheared between two concentric cylinders with frame rates as high as 10,000 images per second, while simultaneously monitoring the shear rate, shear stress, and viscosity as a function of time. The capacities of this "rheo-ultrasound" instrument are illustrated on two examples: (i) the classical case of the Taylor-Couette instability in a simple viscous fluid and (ii) the unstable shear-banded flow of a non-Newtonian wormlike micellar solution.

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arXiv2011

Lift and drag forces on an inclined plow moving over a granular surface

We studied the drag and lift forces acting on an inclined plate while it is dragged on the surface of a granular media, both in experiment and numerical simulation. In particular, we investigated the influence of the horizontal velocity of the plate and its angle of attack. We show that a steady wedge of grains is moved in front of the plow and that the lift and drag forces are proportional to the weight of this wedge. These constants of proportionality vary with the angle of attack but not (or only weakly) on the velocity. We found a universal effective friction law which accounts for the dependence on all the above-mentioned parameters. The stress and velocity fields are calculated from the numerical simulations and show the existence of a shear band under the wedge and that the pressure is non-hydrostatic. The strongest gradients in stress and shear occur at the base of the plow where the dissipation rate is therefore highest.

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arXiv2011

Stress overshoot in a simple yield stress fluid: an extensive study combining rheology and velocimetry

We report a large amount of experimental data on the stress overshoot phenomenon which takes place during start-up shear flows in a simple yield stress fluid, namely a carbopol microgel. A combination of classical rheological measurements and ultrasonic velocimetry makes it possible to get physical insights on the transient dynamics of both the stress $σ(t)$ and the velocity field across the gap of a rough cylindrical Couette cell during the start-up of shear under an applied shear rate $\dotγ$. (i) At small strains ($γ<1$), $σ(t)$ increases linearly and the microgel undergoes homogeneous deformation. (ii) At a time $t_m$, the stress reaches a maximum value $σ_m$ which corresponds to the failure of the microgel and to the nucleation of a thin lubrication layer at the moving wall. (iii) The microgel then experiences a strong elastic recoil and enters a regime of total wall slip while the stress slowly decreases. (iv) Total wall slip gives way to a transient shear-banding phenomenon, which occurs on timescales much longer than that of the stress overshoot and has been described elsewhere [Divoux \textit{et al., Phys. Rev. Lett.}, 2010, \textbf{104}, 208301]. This whole sequence is very robust to concentration changes in the explored range ($0.5 \le C \le 3%$ w/w). We further demonstrate that the maximum stress $σ_m$ and the corresponding strain $γ_m=\dotγt_m$ both depend on the applied shear rate $\dot γ$ and on the waiting time $t_w$ between preshear and shear start-up: they remain roughly constant as long as $\dotγ$ is smaller than some critical shear rate $\dotγ_w\sim 1/t_w$ and they increase as weak power laws of $\dot γ$ for $\dotγ> \dotγ_w$ [...].

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arXiv2011

Interplay between a hydrodynamic instability and a phase transition: the Faraday instability in dispersions of rodlike colloids

Strong effects of the Faraday instability on suspensions of rodlike colloidal particles are reported through measurements of the critical acceleration and of the surface wave amplitude. We show that the transition to parametrically excited surface waves displays discontinuous and hysteretic features. This subcritical behaviour is attributed to the shear-thinning properties of our colloidal suspensions thanks to a phenomenological model based on rheological data under large amplitude oscillatory shear. Birefringence measurements provide direct evidence that Faraday waves induce local nematic ordering of the rodlike colloids. While local alignment simply follows the surface oscillations for dilute, isotropic suspensions, permanent nematic patches are generated by surface waves in samples close to the isotropic-to-nematic transition and above the transition large domains align in the flow direction. This strong coupling between the fluid microstructure and a hydrodynamic instability is confirmed by numerical computations based on the microstructural response of rodlike viruses in shear flow.

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arXiv2010

Shear-induced structuration of confined carbon black gels: Steady-state features of vorticity-aligned flocs

Various dispersions of attractive particles are known to aggregate into patterns of vorticity-aligned stripes when sheared in confined geometries. We report a thorough experimental investigation of such shear-induced vorticity alignment through direct visualization of carbon black gels in both simple plane shear and rotational shear cells. Control parameters such as the gap width, the strain rate, and the gel concentration are systematically varied. It is shown that in steady states the wavelength of the striped pattern depends linearly on the gap width $h$ while being insensitive to both the gel concentration $C$ and the shear rate $\gp$. The width of the vorticity-aligned flocs coincides with the gap width and is also independent of $C$ and $\gp$, which hints to a simple picture in terms of compressible cylindrical flocs. Finally, we show that there exists a critical shear rate $\gp_c$ above which structuration does not occur and that $\gp_c$ scales as $h^{-α}$ with $α=1.4\pm 0.1$ independently of $C$. This extensive data set should open the way to quantitative modelling of the vorticity alignment phenomenon in attractive colloidal systems.

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arXiv2009

Influence of boundary conditions on yielding in a soft glassy material

The yielding behavior of a sheared Laponite suspension is investigated within a 1 mm gap under two different boundary conditions. No-slip conditions, ensured by using rough walls, lead to shear localization as already reported in various soft glassy materials. When apparent wall slip is allowed using a smooth geometry, the sample is shown to break up into macroscopic solid pieces that get slowly eroded by the surrounding fluidized material up to the point where the whole sample is fluid. Such a drastic effect of boundary conditions on yielding suggests the existence of some macroscopic characteristic length that could be connected to cooperativity effects in jammed materials under shear.

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