Pierre Jop

Pierre Jop
CNRS/ Saint-Gobain UMR 125 · Laboratoire Surface du Verre et Interfaces

PhD

About

51
Publications
7,389
Reads
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3,497
Citations
Additional affiliations
October 2009 - June 2015
French National Centre for Scientific Research
Position
  • Researcher
October 2009 - June 2015
Laboratoire Surface du Verre et Interfaces CNRS/ Saint-Gobain UMR 125
Position
  • Researcher

Publications

Publications (51)
Article
Full-text available
Modelling the flow of dry granular materials entering water is crucial for optimizing blending processes in industry and for natural hazard assessment when describing tsunami waves induced by landslides. In this study, we experimentally investigate the case of a jet of grains entering from the air into a water bath. After an initial transient state...
Article
Full-text available
Wet granulation processes can be driven from low to high water content. In this study, we consider the model situation of the growth of a single wet aggregate rolling in a dry granular flow inside a rotating drum. We measure the time evolution of its diameter for different grains and liquids, as well as various rotation rates of the drum. Using X-r...
Conference Paper
Full-text available
A bidisperse medium of large sand particles and small glass beads is mixed in a cylindrical vessel that is put in rotational motion around an eccentric static rod. The subsequent segregation occurring in the system is investigated primarily at the free-surface where the large particles concentration globally increases towards a limit value while os...
Preprint
Full-text available
The fragmentation of liquid sheets produces a collection of droplets. The size distribution of the droplets has a considerable impact on the coating efficiency of sprays and the transport of contaminants. Although many processes commonly used particulate suspensions, the influence of the particles on the spreading dynamics of the sheet and its subs...
Article
Full-text available
The fragmentation of liquid sheets produces a collection of droplets. The size distribution of the droplets has a considerable impact on the coating efficiency of sprays and the transport of contaminants. Although many processes commonly used particulate suspensions, the influence of the particles on the spreading dynamics of the sheet and its subs...
Article
Le comportement des matériaux granulaires humides hétérogènes, éléments incontournables de nombreux processus industriels et géophysiques, résiste encore à une modélisation complète. L’interaction des grains avec une phase liquide doit être éclaircie afin d’optimiser les procédés de mélange, notamment la dispersion des grains d’un agrégat cohésif....
Article
Full-text available
We consider the rearrangements of a vertical two-dimensional granular packing induced by the withdrawal of an intruder. Here, we focus on the influence of the size of the intruder on the reorganization process. The long term evolution of the granular packing is investigated as well as the avalanche dynamics that characterize the short term rearrang...
Preprint
Full-text available
We consider the rearrangements of a vertical twodimensional granular packing induced by the withdrawal of an intruder. Here, we focus on the influence of the size of the intruder on the reorganization process. The long term evolution of the granular packing is investigated as well as the avalanche dynamics that characterize the short term rearrange...
Preprint
Applying mechanical perturbations in a granular assembly may rearrange the configuration of the particles. However, the spatial propagation of an event is not related to the size of the external perturbation alone. Thus, the characteristic length scale of an event is not well defined. In this study, we trigger rearrangements by driving two intruder...
Article
Full-text available
Under suitable conditions, an immersed granular bed can be destabilized by local thermal forcing and the induced buoyant force. The destabilization is evident from the triggering and establishment of a dense fluid-like granular plume. Varying the initial granular layer average height $h$ , a time series of the free layer surface is extracted, allow...
Article
Full-text available
Applying mechanical perturbations in a granular assembly may rearrange the configuration of the particles. However, the spatial propagation of an event is not related to the size of the external perturbation alone. Thus, the characteristic length scale of an event is not well defined. In this study, we trigger rearrangements by driving two intruder...
Article
Wet granular aggregates are common precursors of construction materials, food, and health care products. The physical mechanisms involved in the mixing of dry grains with a wet substrate are not well understood and difficult to control. Here, we study experimentally the accretion of dry grains on a wet granular substrate by measuring the growth dyn...
Preprint
Wet granular aggregates are common precursors of construction materials, food, and health care products. The physical mechanisms involved in the mixing of dry grains with a wet substrate are not well understood and difficult to control. Here, we study experimentally the accretion of dry grains on a wet granular substrate by measuring the growth dyn...
Article
Full-text available
Sintering, glass melting and other industrially relevant processes turn batches of grains into homogeneous products. Such processes involve coupled chemical and physical transformations of the granular packing. For sake of simplicity, we study how local evolutions on grains (volume decreases for example) entail mechanical rearrangements in the over...
Article
Full-text available
Many industrial processes, such as surface coating or liquid transport in tubes, involve liquid sheets or thin films of suspensions. In these situations, the thickness of the liquid film becomes comparable to the particle size, which leads to unexpected dynamics. In addition, the classical constitutive rheological law for suspensions cannot be appl...
Article
Full-text available
We study experimentally the growth dynamics of a horizontal wet granular aggregate produced by accretion when a dry granular jet impacts a wet substrate. The tomographic imaging demonstrates that the wet aggregate is fully saturated and its cohesion is related to the capillary suction due to the pressure drop at the liquid/air interface. We highlig...
Article
Full-text available
We study experimentally the rate of chaotic mixing in viscoplastic fluids by using a rod-stirring protocol with a rotating vessel. Only a limited zone localized around the stirring rods is highly sheared at a given time. Using a dyed spot as the initial condition, we measure the decay of concentration fluctuations of dye as mixing proceeds. The mix...
Preprint
Physical and chemical transformation processes in reactive granular media involve the reorganization of the structure. In this paper, we study experimentally the rearrangements of a two-dimensional (2D) granular packing undergoing a localized transformation. We track the position and evolution of all the disks that constitute the granular packing w...
Article
Physical and chemical transformation processes in reactive granular media involve the reorganization of the structure. In this paper, we study experimentally the rearrangements of a two-dimensional (2D) granular packing undergoing a localized transformation. We track the position and evolution of all the disks that constitute the granular packing w...
Article
Full-text available
The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relat...
Article
Full-text available
Recent progresses in understanding the behavior of dense granular flows are presented. After presenting a bulk rheology of granular materials, I focus on the new developments to account for non-local effects, and on ongoing research concerning the surface rheology and the evolution of mechanical properties for heterogeneous systems.
Article
Full-text available
In this letter the capillary rise of yield-stress fluids is investigated experimentally. Contrary to the case of simple fluids, the final height reached by yield-stress fluids weakly depends on the gap and is strongly affected by the yield stress and the hydrodynamic boundary conditions. Such dependences suggest that the capillary rise of yield-str...
Article
Full-text available
Liquid may give strong cohesion properties to a granular medium, and confer a solidlike behavior. We study the erosion of a fixed circular aggregate of wet granular matter subjected to a flow of dry grains inside a half-filled rotating drum. During the rotation, the dry grains flow around the fixed obstacle. We show that its diameter decreases line...
Article
Full-text available
We present experimental results of chaotic mixing of Newtonian fluids and yield-stress fluids using a rod-stirring protocol with a rotating vessel. We show how the mixing of yield-stress fluids by chaotic advection is reduced compared to the mixing of Newtonian fluids and explain our results, bringing to light the relevant mechanisms: the presence...
Article
Liquid may give strong cohesion properties to a granular medium, and confers a solid-like behavior. We study the evolution of a fixed aggregate of wet granular matter subjected to a flow of dry grains. In the confined geometry of a thin cell, the aggregate is hold by the walls, and the dry matter flowing around will pull grains out of the aggregate...
Article
To model the dynamic of landslides, the evolution of the interface between the erodible ground and the flowing material is still studied experimentally or numerically (ie. Mangeney et al. 2010, Iverson 2012). In some cases, the basal material is more cohesive than the flowing one. Such situation arises for example due to cementation or humidity. Wh...
Article
Using confocal microscopy, we study the flow of a model soft glassy material: a concentrated emulsion. We demonstrate the micro-macro link between in situ measured movements of droplets during the flow and the macroscopic rheological response of a concentrated emulsion, in the form of scaling relationships connecting the rheological "fluidity" with...
Article
Full-text available
This work is devoted to the study of displacement fluctuations of micron-sized particles in an aging colloidal glass. We address the issue of the validity of the fluctuation dissipation theorem (FDT) and the time evolution of viscoelastic properties during aging of aqueous suspensions of a clay (Laponite RG) in a colloidal glass phase. Given the co...
Article
Full-text available
We study the Brownian motion of particles trapped by optical tweezers inside a colloidal glass (Laponite) during the sol-gel transition. We use two methods based on passive rheology to extract the effective temperature from the fluctuations of the Brownian particles. All of them give a temperature that, within experimental errors, is equal to the h...
Article
Full-text available
We study experimentally and theoretically the probability density functions of the injected and dissipated energy in a system of a colloidal particle trapped in a double-well potential periodically modulated by an external perturbation. The work done by the external force and the dissipated energy are measured close to the stochastic resonance wher...
Article
Full-text available
We present simulations of granular flows in a modified Couette cell, using a continuum model recently proposed for dense granular flows. Based on a friction coefficient, which depends on an inertial number, the model captures the positions of the wide shear bands. We show that a smooth transition in velocity-profile shape occurs when the height of...
Article
Full-text available
We study experimentally the fluctuations of the injected and dissipated energy in a system of a colloidal particle trapped in a double-well potential periodically modulated by an external perturbation. The work done by the external force and the dissipated energy are measured close to the stochastic resonance where the injected power is maximum. We...
Preprint
We present simulations of granular flows in a modified Couette cell, using a continuum model recently proposed for dense granular flows. Based on a friction coefficient, which depends on an inertial number, the model captures the positions of the wide shear bands. We show that a smooth transition in velocity-profile shape occurs when increasing the...
Preprint
We study experimentally the fluctuations of the injected and dissipated energy in a system of a colloidal particle trapped in a double well potential periodically modulated by an external perturbation. The work done by the external force and the dissipated energy are measured close to the stochastic resonance where the injected power is maximum. We...
Article
Full-text available
We experimentally investigate how a long granular pile confined in a narrow channel destabilizes when it is inclined above the angle of repose. A uniform flow then develops, which is localized at the free surface. It first accelerates before reaching a steady uniform regime. During this process, an apparent erosion is observed and the thickness of...
Article
Full-text available
We measure the fluctuations of the position of a silica bead trapped by an optical tweezers during the aging of a Laponite suspension. We find that the effective temperature is equal to the bath temperature.
Preprint
A continuum description of granular flows would be of considerable help in predicting natural geophysical hazards or in designing industrial processes. However, the constitutive equations for dry granular flows, which govern how the material moves under shear, are still a matter of debate. One difficulty is that grains can behave like a solid (in a...
Article
Recent experiments and numerical simulations of dry granular flows suggest that a simple rheological description in terms of a friction coefficient varying both with shear rate and pressure through a dimensionless inertial number may be sufficient to capture the major properties of granular flows. In this paper we first present the empirical consti...
Article
Full-text available
A continuum description of granular flows would be of considerable help in predicting natural geophysical hazards or in designing industrial processes. However, the constitutive equations for dry granular flows, which govern how the material moves under shear, are still a matter of debate. One difficulty is that grains can behave like a solid (in a...
Article
Full-text available
In this paper we study the steady uniform flows that develop when granular material is released from a hopper on top of a static pile in a channel. More specifically, we focus on the role of sidewalls by carrying out experiments in set-up of different widths, from narrow channels 20 particle diameters wide to channels 600 particle diameters wide. R...
Article
Recent experiments and numerical simulations of dry and dense granular flows suggest that a simple rheological description, in terms of a shear rate dependent friction coefficient, may be sufficient to capture the major flow properties [1,2]. In this work we generalize this approach by proposing a tensorial form of this rheology leading to 3D hydro...
Article
Full-text available
We propose a new micromechanical approach to probe bending rigidity at molecular scale. Long flexible filaments made of magnetic colloids and linkers are shown to adopt under magnetic field a hairpin configuration. Measuring the hairpin curvature as a function of the field intensity and the linker length from diffracted light allows us to deduce th...
Article
Full-text available
Flows of granular material on a heap is experimentally investigated. A layer of granular material is flowing from a hopper on top of a static pile in a channel. We study the role of the side walls and show that it has a dramatic influence on the dynamics of the flow. The angle of the free surface increases with flow rate for narrow channels but rem...

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