S. Manneville

An initially solid colloidal gel submitted to an oscillatory stress shows complex space- and time-dependence that eventually leads to bulk fluidization with characteristic times consistent with both activated phenomena and Basquin law of fatigue.

The rheology of NFC suspensions that exhibited different microstructures and colloidal stability, namely TEMPO and enzymatic NFC suspensions, was investigated at the macro and mesoscales using a transparent Couette rheometer combined with optical observations and ultrasonic speckle velocimetry (USV). Both NFC suspensions showed a complex rheology, which was typical of yield stress, non-linear and thixotropic fluids. Hysteresis loops and erratic evolutions of the macroscale shear stress were also observed, thereby suggesting important mesostructural changes and/or inhomogeneous flow conditions. The in situ optical observations revealed drastic mesostructural changes for the enzymatic NFC suspensions, whereas the TEMPO NFC suspensions did not exhibit mesoscale heterogeneities. However, for both suspensions, USV measurements showed that the flow was heterogeneous and exhibited complex situations with the coexistence of multiple flow bands, wall slippage and possibly multidimensional ef...

L'interaction son-ecoulement represente une source d'information non intrusive en hydrodynamique. Par exemple, en traversant un tourbillon, une onde acoustique est advectee, refractee, et eventuellement diffusee. L'analyse des deformations du front d'onde conduit alors a une mesure des principales caracteristiques du vortex (position, taille et circulation). Dans une premiere partie experimentale, nous montrons comment le retournement temporel permet d'amplifier l'effet d'un vortex sur une onde ultrasonore. L'utilisation de reseaux de transducteurs autorise une mesure a la fois spatiale et dynamique. Cette technique en transmission est testee sur trois ecoulements modeles dans l'eau. Apres avoir identifie et quantifie les differentes sources de bruit ou d'incertitude, nous validons notre technique par l'etude de la precession et de l'instabilite d'un vortex etire. Nous mettons clairement en evidence la diffusion du son par un filament de vorticite. La seconde partie vise a simuler numeriquement nos experiences. L'interaction son-ecoulement est traitee par trois methodes completement differentes : trace de rayons acoustiques, equation parabolique et differences finies. Ces simulations permettent d'etudier la validite de diverses approximations classiques pour la propagation du son en milieu mobile ainsi que l'influence de l'ouverture finie du faisceau incident. De plus, la prise en compte de la diffusion permet une tres bonne modelisation des donnees experimentales et conduit a une estimation de la taille du vortex. Enfin, nous proposons une etude numerique de l'onde diffusee par un tourbillon. Nous concluons ce travail en decrivant une nouvelle technique d'imagerie 2d d'un ecoulement : l'inter-correlation de speckle acoustique. Cette technique ultra-rapide est basee sur l'analyse du champ de pression retro-diffuse par un fluide ensemence de particules. Nous presentons des resultats preliminaires prometteurs qui viennent completer ceux obtenus en transmission.

... Sébastien Manneville1, Ronald A. Roy2, Charles A. DiMarzio3 and David A. Boas4 1 Centre de Recherche Paul Pascal, Pessac, France 2 Boston University, Boston MA 3 Northeastern University, Boston MA 4 Mass. ... (1995), Boccara et al. (1999), DiMarzio et al. (1999) ...

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Even in simple geometries, many complex fluids display nontrivial flow fields, with regions where shear is concentrated. The possibility for such shear banding has been known for several decades, but in recent years, we have seen an upsurge in studies offering an ever-more precise understanding of the phenomenon. The development of new techniques to probe the flow on multiple scales with increasing spatial and temporal resolution has opened the possibility for a synthesis of the many phenomena that could only have been thought of separately before. In this review, we bring together recent research on shear banding in polymeric and soft glassy materials and highlight their similarities and disparities.

ABSTRACT A combined two-dimensional Rheo-NMR velocimetry and two-dimensional Rheo-USV approach is used to further elucidate the flow of a wormlike micellar solution in cylindrical Couette geometries. Recent experimental enhancements for both methods enable a more detailed description of the flow dynamics than available in the past. This enabled us to revisit and investigate shear banded flow utilizing improved spatial and temporal resolution, clearly confirming a departure from a simple lever rule for the micellar solution under study. Both experimental techniques observe different shear rates in the high shear rate band accompanied by a varying position of the interface between bands for different applied shear rates. Furthermore, spatially and temporally resolved velocimetry reveals various flow instabilities. Ultrasound measurements show vorticity undulations with wavelengths that scale linearly with the size of the high shear rate band. For high enough shear rates, the occurrence of turbulent bursts is detected in the USV case. However, no direct evidence of these bursts is found in the NMR measurements for equivalent shear rates, which we attribute so far to differences in the design of the shearing geometries.

In many situations in physics as well as in some applied sciences, one is faced to the problem of characterizing very irregular functions [1–8]. The examples range from plots of various kind of random walks, e.g. Brownian signals [9], to financial time-series [1], to geological shapes [1,6], to medical time-series [5], to interfaces developing in far from equilibrium growth processes [3,4,8], to turbulent velocity signals [7,10] and to “DNA walks” coding nucleotide sequences [11,12]. These functions can be qualified as fractal functions [1,2,9] whenever their graphs are fractal sets in ℝ 2 (for our purpose here we will only consider functions from ℝ to ℝ). They are commonly called self-affine functions since their graphs are similar to themselves when transformed by anisotropic dilations: ∀ x0 ∈ ℝ,∃H ∈ ℝ; such that for any λ > 0, one has $$f\left( {{x_0} + \lambda x} \right) - f\left( {{x_0}} \right) \simeq {\lambda ^H}\left( {f\left( {{x_0} + x} \right) - f\left( {{x_0}} \right)} \right)$$ (1)

Qu'il s'agisse d'agro-alimentaire ou de cosmetiques, d'emballages polymeres ou d'ecrans a cristaux liquides, la « matiere molle » est au cœur de notre vie quotidienne. La description et la comprehension de l'effet d'une deformation ou d'un ecoulement sur les materiaux mous presentent donc des enjeux industriels considerables tout en soulevant des questions fondamentales sur lesquelles les physiciens se penchent depuis plusieurs decennies. Nous evoquons ici quelques avancees effectuees dans ce domaine grâce a l'emergence de nouvelles techniques qui permettent de sonder la matiere molle, telles que les solutions de micelles geantes ou les materiaux a seuil, entre lesquels on a decouvert des similitudes surprenantes.

ABSTRACT A layer of simple fluid under vertical vibrations undergoes the well‐known Faraday instability: above a critical acceleration ac, the surface becomes unstable and ripples organize into patterns characterized by a critical wave number kc. In this work, we investigate the effect of vertical vibrations on a layer of “wormlike micelles,” a very viscoelastic fluid. The onset of the Faraday instability is shown to be strongly affected by viscoelasticity: elastic waves between the surface of the fluid and the bottom of the container may enhance or hinder the instability depending on the vibration frequency f. In order to better demonstrate such an elastic effect, we perform particle imaging velocimetry as well as birefringence experiments to access the velocity and the stress fields. Our measurements unveil the existence of “elastic rolls” that duplicate the surface wave pattern over the whole depth of the fluid. © 2006 American Institute of Physics