Growing of hexagonal compact domains in a granular compaction experiment. Watch the movie

Flowing of metallic balls in a rotating drum

Vibrated granular layer. Watch the movie

### Position

Lecturer at the University of Liège
Chair : Soft Matter Physics and Complex Systems
Research Group : www.grasp-lab.org
Technological platform : www.aptis.be

### Research

#### Keywords

Soft matter - Self Assembly processes - Active materials - Static, quasistatic and dynamical properties of granular materials - Cohesive granular materials - Effect of a magnetic and electric field on a granular material - Biomechanics and biofluids

#### Research project

The first axis of my research project is dedicated to the experimetal studies of granular materials properties. A granular material is a conglomeration of discrete solid particles. This material can be separated in two categories : cohesive and non-cohesive. Indeed, the humidity, the electrostatic charges and the Van der Waals interactions induce some cohesion between the grains. When the weight of one grain is higher than the cohesive forces, the material is non-cohesive. These materials have been intensively studied during the last decades because of the rich variety of their physical properties. On the other hand, if the cohesive forces are higher than the weight of one grain, these forces will strongly modify the properties of the pile. Among these cohesive granular materials, powders are used in many research domains : chemistry, pharmacy, engineering... Nowadays, the processes used for the manipulation of powders are mainly based on empirical knowledge. However, the complexity of the methods used in these research domains induce the necessity of more rigorous knowledge of these materials. Therefore, a fundamental study of cohesive powders is essential.

The difficulty to quantify and to control cohesion between the grains of a powder makes their experimental study very complex. During our previous research, we have developed a controlled cohesive granular material. In this controlled system, the cohesion between the grains can the tuned easily. This controlled material is made of spherical ferromagnetic beads placed in an adjustable magnetic field. This system have been used during my thesis to study the influence of the cohesion on the volumic fraction of a pile (Picking the Packing, Research Highlights in Nature 450, 588 (2007)).

My present research project includes a second axis dedicated to the study of self-assembly processes leading to the formation of mesostructures. Mesostructures are microscopic (typically from 100 nanometers to 100 microns) architectures with complex arrangements which confer them remarkable physical properties. Static and dynamic properties of such structures are investigated using model systems of Soft Matter. This activity is based on expertise acquired during my experimental works on collective motions, and patterning in granular materials. These self-organization processes take place in assemblies of micro and nano particles placed in an external field (magnetic and/or electric) and submitted to geometrical, mechanical, capillary and hydrodynamic constraints. In order to identify and to control the relevant self-assembly processes, the interactions between the particles have to be studied precisely. With a better fundamental understanding of these interactions, the self-organization processes will be obtained through a bottom-up method instead of the classical empirical methods. Then, we will be able to improve the long-range organization in mesostructures, catalyst, porous materials, sintered materials… Moreover, future studies will be dedicated to reversible self-organized systems where the order could be modified in order to obtain smart reconfigurable materials.

To obtain more details about my works concerning granular materials, see the topic “ The physics of sandpiles ” in the “Reflections” website of the University of Liege.

I am involved in the new platform Aptis dedicated to powder characterization. I am working on the development of new measurement apparatus dedicated to the characterization of powder flow properties.

#### Publications

1. Compaction of anisotropic granular materials: Experiments and simulations
G. Lumay and N. Vandewalle
Phys. Rev. E 70, 051314 (2004)
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2. Grain mobility and hexagonal domains formation in 2d granular compaction
G. Lumay and N. Vandewalle
Powders & Grains 1, 343 (2005)
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3. Experimental Study of Granular Compaction Dynamics at Different Scales: Grain Mobility, Hexagonal Domains, and Packing Fraction
G. Lumay and N. Vandewalle
Phys. Rev. Lett. 95, 028002 (2005)
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4. Experimental study of the compaction dynamics for two-dimensional anisotropic granular materials
G. Lumay and N. Vandewalle
Phys. Rev. E 74, 021301 (2006)
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5. Compaction of granular materials: experiments and contact dynamics simulations
G Lumay, F Ludewig and N Vandewalle
J. Phys.: Conf. Ser. 40, 133 (2006)
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6. Linking compaction dynamics to the flow properties of powders
G. Lumay, C. Bodson, L. Delattre, O. Gerasimov and N. Vandewalle
Appl. Phys. Lett. 89, 093505 (2006)
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7. Precursors to avalanches in a granular monolayer
T. Scheller, C. Huss, G. Lumay, N. Vandewalle and S. Dorbolo
Phys. Rev. E 74, 031311 (2006)
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8. The influence of grain shape, friction and cohesion on granular compaction dynamics
N. Vandewalle,G. Lumay G,O. Gerasimov,F. Ludewig
Eur. Phys. J. E 22, 241 (2007)
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9. Swarming and swirling in self-propelled polar granular rods
Arshad Kudrolli, Geoffroy Lumay, Dmitri Volfson, Lev S. Tsimring
Phys. Rev. Lett. 100, 058001 (2008)
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10. TUNABLE RANDOM PACKINGS
G.Lumay and N.Vandewalle
New J. of Phys. 9, 406 (2007)
We present an experimental protocol that allows to tune the packing fraction $\eta$ of a random pile of ferromagnetic spheres from a value close to the lower limit of random loose packing $\eta_{RLP} \simeq 0.56$ to the upper limit of random close packing $\eta_{RCP} \simeq 0.64$. This broad range of packing fraction values are obtained under normal gravity, but we apply a magnetically controlled cohesion between the grains during the formation of the pile. After the formation of the pile, the induced cohesion is decreased continuously along a linear decreasing ramp. The controlled collapse of the pile is found to generate various and reproducible values of the random packing fraction $\eta$.
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11. Stationary states in 1D system of inelastic particles
O. Gerasymov, N. Vandewalle, A.Ya. Spivk, N.N. Khudyntsev, G. Lumay, S. Dorbolo, O.A. Klymenkov
Ukr. Journ. Phys. 53, 1128 (2008)
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12. The controlled flow of Smart Powders
G. Lumay and N. Vandewalle
Phys. Rev. E 78, 061302 (2008)
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13. Motion of carbon nanotubes in a rotating drum: The dynamic angle of repose and a bed behavior diagram
S. L. Pirard, G. Lumay, N. Vandewalle and J.-P. Pirard
Chem. Eng. J. 146, 143 (2009)
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14. Mullite coatings on ceramic substrates: stabilisation of Al2O3-SiO2 suspensions for spray drying of composite granules suitable for reactive plasma spray
A. Schrijnemakers, S. Andre, G. Lumay, N. Vandewalle, F. Boschini, R. Cloots, B. Vertruyen
J. of Eur. ceramic soc. 29, 2169 (2008)
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15. Kinetic Energy Fluctuations and Diffusivity in a 2D Vibrated Granular Packing
Rim Harich, Geoffroy Lumay and Eric Clement
TRAFFIC AND GRANULAR FLOW 2007 , 597 (2007)
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16. Packing fraction and compaction dynamics of magnetic powders
G. Lumay & N. Vandewalle
AIP Conf. Proc. 1145, 131-134 (2009)
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17. Flow properties and heap shape of magnetic powders
N. Vandewalle & G. Lumay
AIP Conf. Proc. 1145, 135-138 (2009)
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18. Compaction dynamics of a magnetized powder
G. Lumay, S. Dorbolo & N. Vandewalle
Phys. Rev. E 80, 041302 (2009)
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19. Effect of an electric field on an intermittent granular flow
E. Mersch, G. Lumay, F. Boschini & N. Vandewalle
Phys. Rev. E 81, 041309 (2010)
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20. Compaction dynamics of wet granular assemblies
J.E. Fiscina, G. Lumay, F. Ludewig & N. Vandewalle
Phys. Rev. Lett. 105, 048001 (2010)
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21. Flow of magnetized grains in a rotating drum
G. Lumay & N. Vandewalle
Phys. Rev. E 82, 040301(R) (2010)
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22. A pendulum test as a tool to evaluate viscous friction parameters in the equine fetlock joint
P. Noble, G. Lumay, M. Coninx, B. Collin, A. MagnŽe, J. Lecomte-Beckers, J. M. Denoix & D. Serteyn
The Veterinary Journal 188, 204 (2011)
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23. Influence of a reduced gravity on the volume fraction of a monolayer of spherical grains
S. Dorbolo, T. Scheller, F. Ludewig, G. Lumay & N. Vandewalle
Phys. Rev. E 84, 041305 (2011)
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24. Granular gas in a periodic lattice
S. Dorbolo, M. Brandenbourger, F. Damanet, H. Dister, F. Ludewig, D. Terwagne, G. Lumay, and N. Vandewalle
Eur. Phys. J. E 32, 1465 (2011)
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25. Measuring the flowing properties of powders and grains
G. Lumay, F. Boschini, K. Traina, S. Bontempi, J.-C. Remy, R. Cloots & N. Vandewalle
Powder Technology Status: accepted,  (2012)
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26. How relative humidity affects random packing experiments
N.Vandewalle, G.Lumay, F.Ludewig & J.E.Fiscina
Phys. Rev. E Status: submitted,  (2012)
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