Biomedical subjects

François Lequeux

Publications and source records attributed to François Lequeux.

6 recordsLinked to original sources

PubMed2005

Subdiffusion and dynamical heterogeneities in a lattice glass model.

We study a kinetically constrained lattice glass model in which continuous local densities are randomly redistributed on neighboring sites with a kinetic constraint that inhibits the process at high densities, and a random bias accounting for attractive or repulsive interactions. The full steady-state distribution can be computed exactly in any space dimension d. Dynamical heterogeneities are characterized by a length scale that diverges when approaching the critical density. The glassy dynamics of the model can be described as a reaction-diffusion process for the mobile regions. The motion of mobile regions is found to be subdiffusive, for a large range of parameters, due to a self-induced trapping mechanism.

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PubMed2005

Slow flows of yield stress fluids: Complex spatiotemporal behavior within a simple elastoplastic model.

A minimal athermal model for the flow of dense disordered materials is proposed, based on two generic ingredients: local plastic events occuring above a microscopic yield stress, and the nonlocal elastic release of the stress these events induce in the material. A complex spatiotemporal rheological behavior results, with features in line with recent experimental observations. At low shear rates, macroscopic flow actually originates from collective correlated bursts of plastic events, taking place in dynamically generated fragile zones. The related correlation length diverges algebraically at small shear rates. In confined geometries, bursts occur preferentially close to the walls, yielding an intermittent form of flow localization.

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PubMed2003

Aging and nonlinear rheology in suspensions of polyethylene oxide-protected silica particles.

In an attempt to establish connections between classical rheology and aging in paste colloidal suspensions, we report in this paper a large set of experimental results on a given system. We have studied suspensions of polyethylene oxide-protected silica particles and performed classical rheology experiments that exhibit a very nonlinear behavior. We have then evidenced aging through stress relaxation as observed in various glassy systems, and finally show other manifestations of aging through various rheological experiments. Qualitative agreement between these experimental results and the predictions of a simple model suggests that the behavior observed experimentally is governed by the competition between aging and mechanically induced rejuvenation.

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PubMed2003

How are colloidal suspensions that age rejuvenated by strain application?

We present here a microscopic study of the effect of shear on a dense purely repulsive colloidal suspension. We use multispeckle diffusing wave spectroscopy to monitor the transient motions of colloidal particles after being submitted to an oscillatory strain. This technique proves efficient to record the time evolution of the distribution of relaxation times. After a high oscillatory shear, we show that this distribution displays full aging behavior. Conversely, when a moderate shear is applied the distribution is modified in a non-trivial way. Whereas high shear is able to erase all the sample history and rejuvenate it, a moderate shear helps it to age. We call this phenomenon overaging. We demonstrate that overaging can be understood if the complete shape of the relaxation time distribution is taken into account. We finally report how the soft glassy rheology model accounts for this effect.

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PubMed2002

Simple model for heterogeneous flows of yield stress fluids.

Various experiments evidence spatial heterogeneities in sheared yield stress fluids. To account for heterogeneities in the velocity gradient direction, we use a simple model corresponding to a nonmonotonic local flow curve and study a simple shear geometry. Different types of boundary conditions are considered. Under controlled macroscopic shear stress Sigma, we find homogeneous flow in the bulk and a hysteretic macroscopic stress-shear-rate curve. Under controlled macroscopic shear rate Gamma;, shear banding is predicted within a range of values of Gamma;. For small shear rates, stick-slip can also be observed. These qualitative behaviors are robust to changes in the boundary conditions.

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PubMed2002

Rejuvenation and overaging in a colloidal glass under shear.

We report the modifications of the microscopic dynamics of a colloidal glass submitted to shear. We use multispeckle diffusing wave spectroscopy to monitor the evolution of the spontaneous slow relaxation processes after the samples have been submitted to various straining. We show that high shear rejuvenates the system and accelerates its dynamics, whereas moderate shear over-ages the system. We analyze these phenomena within the frame of the Bouchaud's trap model.

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