Papers by Julien Schockmel
Physical Review E, 2020
We perform three-dimensional particle-based simulations of confined, vibrated, and magnetizable b... more We perform three-dimensional particle-based simulations of confined, vibrated, and magnetizable beads to study the effect of cell geometry on pattern selection. For quasi-two-dimensional systems, we reproduce previously observed macroscopic patterns such as hexagonal crystals and labyrinthine structures. For systems at the crossover from two to three dimensions, labyrinthine branches shorten and are replaced by triplets of beads forming upright triangles which self-organize into a herringbone pattern. This transition is associated with increases in both translational and orientational orders.
Review of Scientific Instruments, 2018
A new experimental facility has been designed and constructed to study driven granular media in a... more A new experimental facility has been designed and constructed to study driven granular media in a low-gravity environment. This versatile instrument, fully automatized, with a modular design based on several interchangeable experimental cells, allows us to investigate research topics ranging from dilute to dense regimes of granular media such as granular gas, segregation, convection, sound propagation, jamming, and rheology—all without the disturbance by gravitational stresses active on Earth. Here, we present the main parameters, protocols, and performance characteristics of the instrument. The current scientific objectives are then briefly described and, as a proof of concept, some first selected results obtained in low gravity during parabolic flight campaigns are presented.
EPJ Web of Conferences, 2017
It is well known in industrial applications involving powders and granular materials that the rel... more It is well known in industrial applications involving powders and granular materials that the relative air humidity and the presence of electrostatic charges influence drastically the material flowing properties. The relative air humidity induces the formation of capillary bridges and modify the grain surface conductivity. The presence of capillary bridges produces cohesive forces. On the other hand, the apparition of electrostatic charges due to the triboelectric effect at the contacts between the grains and at the contacts between the grains and the container produces electrostatic forces. Therefore, in many cases, the powder cohesiveness is the result of the interplay between capillary and electrostatic forces. Unfortunately, the triboelectric effect is still poorly understood, in particular inside a granular material. Moreover, reproducible electrostatic measurements are difficult to perform. We developed an experimental device to measures the ability of a powder to charge electrostatically during a flow in contact with a selected material. Both electrostatic and flow measurements have been performed in different hygrometric conditions. The correlation between the powder electrostatic properties, the hygrometry and the flowing behavior are analyzed.
Physical Review E, 2017
We present a systematic experimental study of the confinement effect on the crystallization of a ... more We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short range magnetic dipole-dipole potential induced by an external magnetic field. The grains are confined by repulsing walls and are homogeneously distributed inside the cell. A two-dimensional (2d) Brownian motion is induced by horizontal mechanical vibrations. Therefore, the balance between magnetic interaction and agitation allows investigating 2d phases through direct visualization. The effect of both confinement size and shape on the grains' organization in the low-energy state has been investigated. Concerning the confinement shape, triangular, square, pentagonal, hexagonal, heptagonal, and circular geometries have been considered. The grain organization was analyzed after a slow cooling process. Through the measurement of the averaged bond order parameter for the different confinement geometries, it has been shown that cell geometry strongly affects the ordering of the system. Moreover, many kinds of defects, whose observation rate is linked to the geometry, have been observed: disclinations, dislocations, defects chain, and also more exotic defects such as a rosette. Finally, the influence of confinement size has been investigated and we point out that no finite-size effect occurs for a hexagonal cell, but the finite-size effect changes from one geometry to another.
Papers in Physics, 2015
During a typical silo discharge, the material flow rate is determined by the contact forces betwe... more During a typical silo discharge, the material flow rate is determined by the contact forces between the grains. Here, we report an original study concerning the discharge of a two-dimensional silo filled with repelling magnetic grains. This non-contact interaction leads to a different dynamics from the one observed with conventional granular materials. We found that, although the flow rate dependence on the aperture size follows roughly the power-law with an exponent 3/2 found in non-repulsive systems, the density and velocity profiles during the discharge are totally different. New phenomena must be taken into account. Despite the absence of contacts, clogging and intermittence were also observed for apertures smaller than a critical size determined by the effective radius of the repulsive grains. Received: 10 July 2015, Accepted: 7 August 2015; Edited by: L. A. Pugnaloni; Reviewed by: J. R. Darias, Universidad Simón o Bolívar, Caracas, Venezuela; DOI: http://dx.doi.org/10.4279/PI...
Physical Review E, 2011
We report experiments on soap film configurations in a triangular prism for which the shape facto... more We report experiments on soap film configurations in a triangular prism for which the shape factor can be changed continuously. Two stable configurations can be observed for a range of the shape factor h, being the prism-height/edge-length ratio. A hysteretic behavior is found, due to the occurence of another local minima in the free energy. Contrary to a common belief, soap films can be trapped in a particular configuration being different from a global surface minimization. This metastability can be evidenced from a geometrical model based on idealized structures. Depending on the configuration, the transition is either first or second order, providing clues on the structural relaxations taking place into three-dimensional foams, such as T1 rearrangements.
Physical Review E, 2013
We present an experimental model system to study two-dimensional phase transitions. This system i... more We present an experimental model system to study two-dimensional phase transitions. This system is composed of a monolayer of millimetric beads interacting through shor range magnetic dipole-dipole interactions. As the system is athermal, a mechanical agitation is used to produce an erratic motion of the beads. The two-dimensional melting scenario predicted by the Kosterlitz-Thouless-Halperin-Nelson-Young theory is observed. Each phase (liquid-hexatic-solid) has been highlighted with the use of both static and dynamic order parameters. Translational and orientational order are, respectively, estimated through the pair correlation function g(r) and both orientational correlation function g 6 (r) and its temporal counterpart g 6 (t). We observe two transitions by tuning the applied magnetic field H. First, a loss of translational order without loss of orientational order is observed. This is the signature of the transition from the solid phase to the so-called "hexatic" phase. Finally, the orientational order disappears, leading to a liquidlike structure.
Memory effects in soap film arrangements NICOLAS VANDE-WALLE, STEPHANE DORBOLO, GEOFFROY LUMAY, J... more Memory effects in soap film arrangements NICOLAS VANDE-WALLE, STEPHANE DORBOLO, GEOFFROY LUMAY, JULIEN SCHOCK-MEL, MARTIAL NOIRHOMME, GRASP, Institute of Physics B5a, University of Liege, B4000 Liege -We report experiments on soap film configurations in a triangular prism for which the shape factor can be changed continuously. Two stable configurations can be observed for a range of the shape factor h. A hysteretic behaviour is found, due to the occurence of another local minima in the free energy. Experiments demonstrate that soap films can be trapped in a particular configuration being different from a global surface minimization. This metastability can be evidenced from a geometrical model based on idealized structures. Depending on the configuration, providing clues on the structural relaxations taking place into 3D foams, such as T1 rearrangements. The composition of the liquid is also investigated leading to dynamical picture of the transition. (Phys. Rev. E 83, 021403 (2011))
Bulletin of the American Physical Society, Mar 4, 2015
Physical review, Jun 15, 2017
We present a systematic experimental study of the confinement effect on the crystallization of a ... more We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short range magnetic dipole-dipole potential induced by an external magnetic field. The grains are confined by repulsing walls and are homogeneously distributed inside the cell. A two-dimensional (2d) Brownian motion is induced by horizontal mechanical vibrations. Therefore, the balance between magnetic interaction and agitation allows investigating 2d phases through direct visualization. The effect of both confinement size and shape on the grains' organization in the low-energy state has been investigated. Concerning the confinement shape, triangular, square, pentagonal, hexagonal, heptagonal, and circular geometries have been considered. The grain organization was analyzed after a slow cooling process. Through the measurement of the averaged bond order parameter for the different confinement geometries, it has been shown that cell geometry strongly affects the ordering of the system. Moreover, many kinds of defects, whose observation rate is linked to the geometry, have been observed: disclinations, dislocations, defects chain, and also more exotic defects such as a rosette. Finally, the influence of confinement size has been investigated and we point out that no finite-size effect occurs for a hexagonal cell, but the finite-size effect changes from one geometry to another.
Papers in Physics, Sep 16, 2015
During a typical silo discharge, the material flow rate is determined by the contact forces betwe... more During a typical silo discharge, the material flow rate is determined by the contact forces between the grains. Here, we report an original study concerning the discharge of a twodimensional silo filled with repelling magnetic grains. This non-contact interaction leads to a different dynamics from the one observed with conventional granular materials. We found that, although the flow rate dependence on the aperture size follows roughly the power-law with an exponent 3/2 found in non-repulsive systems, the density and velocity profiles during the discharge are totally different. New phenomena must be taken into account. Despite the absence of contacts, clogging and intermittence were also observed for apertures smaller than a critical size determined by the effective radius of the repulsive grains.
Physical review, Oct 21, 2020
We perform three-dimensional particle-based simulations of confined, vibrated, and magnetizable b... more We perform three-dimensional particle-based simulations of confined, vibrated, and magnetizable beads to study the effect of cell geometry on pattern selection. For quasi-two-dimensional systems, we reproduce previously observed macroscopic patterns such as hexagonal crystals and labyrinthine structures. For systems at the crossover from two to three dimensions, labyrinthine branches shorten and are replaced by triplets of beads forming upright triangles which self-organize into a herringbone pattern. This transition is associated with increases in both translational and orientational orders.
We present experimental results obtained with a model experimental system dedicated to the study ... more We present experimental results obtained with a model experimental system dedicated to the study of 2D structures and phase transitions. The system is composed of a monolayer of millimetric soft ferromagnetic beads confined in a 2D horizontal cell. The beads are immersed in a vertical and homogeneous magnetic field inducing magnetic dipole-dipole interactions between beads. Due to the confinement, the repulsive interactions tend to order the system. As the system is athermal, a mechanical agitation is used to produce a Brownian motion of the beads which creates disorder. Adjusting the competition between the effects of the interaction and the agitation allows us to control the order of the system. Thanks to this experimental setup, we can study the transition from a frozen and very ordered state, called a crystal, to a disordered and dynamic state similar to a liquid. As predicted by the KTHNY theory of 2D melting, a two-step transition is highlighted, including the so-called hexatic phase between crystal and liquid. In addition, the structures observed agree quantitatively with structures obtained in colloidal systems and in numerical simulations. Our experimental system is, therefore, a suitable model to study 2D thermal structures. In this work, we focus on the study of topological defects that are crucial in low-dimensional physics. We first forced topological defects into the system by inducing frustration from confinement. We show that the size and the geometry of the confinement strongly affect the global order, as well as the type and the number of topological defects observed in the systems. Finally, we force pointlike defects in the structure by introducing beads of different size, called impurities. At global scale, the increase of the impurity can prevent the crystallization. At local scale, we observe that an impurity induces a very localized geometrical frustration, which creates a topological defect whose nature is directly related to the size of the impurity.
Bulletin of the American Physical Society, Mar 17, 2017
Submitted for the MAR17 Meeting of The American Physical Society Combined effect of moisture and ... more Submitted for the MAR17 Meeting of The American Physical Society Combined effect of moisture and electrostatic charges on powder flow GEOFFROY LUMAY, ANTONELLA RESCAGLIO, JULIEN SCHOCKMEL, NICOLAS VANDEWALLE, University of Liege (Belgium)-It is well known in industrial applications involving powders and granular materials that the relative air humidity and the presence of electrostatic charges influence drastically the material flowing properties. The relative air humidity induces the formation of capillary bridges and modify the grain surface conductivity. The presence of capillary bridges produces cohesive forces. On the other hand, the apparition of electrostatic charges due to the triboelectric effect at the contacts between the grains and at the contacts between the grains and the container produces electrostatic forces. Therefore, in many cases, the powder cohesiveness is the result of the interplay between capillary and electrostatic forces. Unfortunately, the triboelectric effect is still poorly understood, in particular inside a granular material. Moreover, reproducible electrostatic measurements are difficult to perform. We developed an experimental device to measures the ability of a powder to charge electrostatically during a flow in contact with a selected material. Both electrostatic and flow measurements have been performed in different hygrometric conditions. The correlation between the powder electrostatic properties, the hygrometry and the flowing behavior are analyzed.
Scientific Reports, Jun 1, 2015
Athermal two-dimensional granular systems are exposed to external mechanical noise leading to Bro... more Athermal two-dimensional granular systems are exposed to external mechanical noise leading to Brownian-like motion. Using tunable repulsive interparticle interaction, it is shown that the same microstructure as that observed in colloidal suspensions can be quantitatively recovered at a macroscopic scale. To that end, experiments on granular and colloidal systems made up of magnetized particles as well as computer simulations are performed and compared. Excellent agreement throughout the range of the magnetic coupling parameter Γ is found for the pair distribution as well as the bond-orientational correlation functions. This finding opens new ways to efficiently and very conveniently explore phase transitions, crystallization, nucleation, etc in confined geometries.
The presence of electrostatic charges inside a powder is known to influence drastically the mater... more The presence of electrostatic charges inside a powder is known to influence drastically the material flowing properties. The triboelectric charges produced at the contacts between the grains and at the contacts between the grains and the container produces electrostatic forces. On the one hand, the triboelectric effect is useful for many applications, but on the other hand, the triboelectrification causes complications. Unfortunately, the triboelectric effect is still poorly understood, even at the fundamental level. The difficulties are related to the non-equilibrium character of the tribolectectric dynamic and to the variety of mechanisms behind this effect. Moreover, reproducible electrostatic measurements are difficult to perform. We developed an experimental device dedicated to the measurement of powder triboelectric properties. This device measures the ability of a powder to charge electrostatically during a flow in contact with a selected material. This measurement is perform...
Bulletin of the American Physical Society, 2015
Phase transitions in a confined monolayer of magnetized beads JULIEN SCHOCKMEL, Univ de Liege -We... more Phase transitions in a confined monolayer of magnetized beads JULIEN SCHOCKMEL, Univ de Liege -We present experimental results obtained with a model experimental system dedicated to the study of 2D phase transitions. The system is composed of millimetric beads interacting through magnetic dipoledipole interaction. Due to the confinement, repulsive interactions tends to order the system. In addition, the system is submitted to a controlled mechanical agitation which produce an erratic motion of the beads and thus creates disorder. Controlling the competition between interaction energy and entropy, allows us to explore different structures of 2 dimensional systems. At first, the melting of a two dimensional crystal is studied. As predicted by the KTHNY theory, a two stage melting is observed, including the so-called hexatic phase (see results in Phys. Rev. E.87, 062201 ( )). Afterward, the behavior of binary systems is studied. In particular, the effect of the grains polydispersity on the order is analyzed.
Threshold of gas-like to clustering transition in driven granular media in low-gravity environment
EPL (Europhysics Letters), 2018
Strongly driven granular media are known to undergo a transition from a gas-like to a cluster reg... more Strongly driven granular media are known to undergo a transition from a gas-like to a cluster regime when the density of particles is increased. However, the main mechanism triggering this transition is not fully understood so far. Here, we investigate experimentally this transition within a 3D cell filled with beads that are driven by two face-to-face vibrating pistons in low gravity during parabolic flight campaigns. By varying large ranges of parameters, we obtain the full phase diagram of the dynamical regimes reached by the out-of-equilibrium system: gas, cluster or bouncing aggregate. The images of the cell recorded by two perpendicular cameras are processed to obtain the profiles of particle density along the vibration axis of the cell. A statistical test is then performed on these distributions to determinate which regime is reached by the system. The experimental results are found in very good agreement with theoretical models for the gas-cluster transition and for the emergence of the bouncing state. The transition is shown to occur when the typical propagation time needed to transmit the kinetic energy from one piston to the other is of the order of the relaxation time due to dissipative collisions
Uploads
Papers by Julien Schockmel