By chance my professional activities are combining my passions for sciences and technologies. I’m using extensively competencies in electronics, programming, and mechanics to develop original measurement devices for research projects and to illustrate my lectures. These competencies were mainly developed in the framework of my hobbies: DIY electronics, aeromodelling, mechanics, blacksmithing and bladesmithing.

Position

• Professor at the University of Liège
  Chair : Soft Matter Physics and Complex Systems
  Department : Physics department of the Faculty of sciences
  
Research Unit : CESAM


• Co-founder of GranuTools company developing and commercializing laboratory instruments for powder characterization: flow, density, cohesiveness, electrostatic properties, ...

Lectures

• General Physics (for students in pharmacy)
• Thermodynamics (for bio-engineers)
• Waves and Quanta (for engineers)
• Techniques of Experimental Physics (for students in physics)
• Numerical tools for Soft Matter Physics (for students in physics)

Some pictures of the experiments performed to illustrate my lectures:

Research

Research strategy - Our strategy to study a physical phenomenon is based on the development of original experimental set-ups to obtain original experimental results. Afterward, physical models are proposed to describe the physical mechanisms and to extract the main parameters. If needed, numerical simulations are conducted to investigate parameters which are difficult to control experimentally. Sometimes, laboratory prototypes developed to perform fundamental studies are becoming commercial instruments.

Physics of powders and granular materials. - A granular material is a conglomeration of discrete solid particles. Granular materials behavior is influenced by (1) steric repulsions, (2) friction forces (3) cohesive forces and (4) interaction with the surrounding gas. The steric repulsion is related to the grain geometry. Friction forces are influenced by both the surface state (rough or smooth surface) and the chemical nature of the grains. Cohesive forces may be induced by the presence of liquid bridges, by electrostatic charges, by van der Waals interactions or more rarely by magnetic dipole-dipole interactions. The predominance of one of these forces depends on both the environmental conditions and the physico-chemical properties of the grains. When the weight of one grain is higher than the cohesive forces, the material is considered as 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 acting on a grain are higher than the weight of the grain, these cohesive forces will drastically modify the properties of the pile. Among these cohesive granular materials, fine powders are used in many research domains : chemistry, pharmacy, engineering... Nowadays, the processes used for the manipulation of powders are still mainly based on empirical knowledge. However, the complexity of the methods used in these domains induces the necessity of more rigorous knowledge of these materials. Therefore, fundamental studies of cohesive powders are still essential.

Model cohesive powders. - The difficulty to quantify and to control cohesion between the grains of a powder makes their experimental study very complex. Therefore, we first used a controlled cohesive powder made of metallic grains in an adjustable magnetic field B [18, 21]. In this controlled system, the cohesion between the grains can the tuned easily through the magnetic field. This system has been used during to study the influence of the cohesion on packing fraction, repose angle, heap shape, flow in silos and on the flow in a rotating drum.

Real cohesive powders. - After the study of model cohesive powders with a fundamental approach, we analyzed (and are still analyzing) the behavior of powders used in the industry with a more practical approach [25]. For that, we developped a range of original set-ups to measure packing dynamics, powder rheology, powder electrostatic properties, cohesiveness,... At the beginning, these set-ups were laboratory prototypes. After repetitive expressions of interest from industries, these methods were adapted to become commercial laboratory instruments: GranuFlow, GranuPack, GranuDrum, GranuHeap, GranuMidity and GranuCharge. These instruments are now commercialized by the company GranuTools.

Combined effect of humidity and electrostatic charges on powders. - When two materials are rubbed, electric charges are exchanged at the surfaces. This contact electrification is an old fundamental scientific subject. However, despite the numerous studies dedicated to this subject, the fundamental mechanisms behind the triboelectric effect are not fully understood in powders and granular materials. The electric charges created by triboelectric effects lead to uncontrolled electric field, electrostatic forces between the grains and/or between the grains and the container. Moisture is known to affect both static and dynamic behaviors of granular materials. Moreover, the effect of moisture is far from obvious due to the interplay with electrostatic effects. Indeed, moisture influences both surface grains conductivity and capillary bridges formation. For low relative air humidity, the electrical conductivity necessary for charge dissipation is reduced. For high relative air humidity, the electrical conductivity increases and liquid bridges may be formed at the contacts between the grains, resulting in sticking. Therefore, the electrical charges are dissipated more easily. However, the apparition of liquid bridges also induces cohesive forces inside the packing. At intermediate relative humidity values the cohesion is expected to be lower. We performed different studies on that topic. In particular, we analyzed the effect of powder flow aid additives (fumed silica, mesoporous silica, stearate, ...) on these cohesive forces.

Self assembly processes - 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.

Publications

3. Experimental Study of Granular Compaction Dynamics at Different Scales: Grain Mobility, Hexagonal Domains, and Packing Fraction Phys. Rev. Lett. 95, 028002 (2005) Show Abstract

11. Swarming and swirling in self-propelled polar granular rods Phys. Rev. Lett. 100, 058001 (2008) Show Abstract