References of "Vandewalle, Nicolas"
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See detailRealization of the Najafi-Golestanian microswimmer
Grosjean, Galien ULg; Hubert, Maxime ULg; Lagubeau, Guillaume et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2016), 94(2), 021101

A paradigmatic microswimmer is the three-linked-spheres model, which follows a minimalist approach for propulsion by shape shifting. As such, it has been the subject of numerous analytical and numerical ... [more ▼]

A paradigmatic microswimmer is the three-linked-spheres model, which follows a minimalist approach for propulsion by shape shifting. As such, it has been the subject of numerous analytical and numerical studies. In this Rapid Communication, an experimental three-linked-spheres swimmer is created by self-assembling ferromagnetic particles at an air-water interface. It is powered by a uniform oscillating magnetic field. A model, using two harmonic oscillators, reproduces the experimental findings. Because the model remains general, the same approach could be used to design a variety of efficient microswimmers. [less ▲]

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See detailSelf-assembly of capillary multipoles
Poty, Martin ULg; Lagubeau, Guillaume; Lumay, Geoffroy ULg et al

Conference (2016, July 21)

Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, millimeter scale objets are produced ... [more ▼]

Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, millimeter scale objets are produced. Their 3d shape is chosen in order to create capillary multipoles. The capillary interactions between these components can be either attractive or repulsive depending on the interface local deformations along the liquid-air interface. In order to understand how the shape of an object deforms the interface, we developed an original profilometry method. The measurements show that specific structures can be programmed by selecting the 3d branched shapes. [less ▲]

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See detailMagnetocapillary self-assemblies: Swimming and micromanipulation
Grosjean, Galien ULg; Hubert, Maxime ULg; Lagubeau, Guillaume et al

Poster (2016, July)

Floating magnetic particles can self-assemble into structures, by a combination of a magnetic dipole-dipole interaction and an attraction due to the interfacial deformation. These structures are ... [more ▼]

Floating magnetic particles can self-assemble into structures, by a combination of a magnetic dipole-dipole interaction and an attraction due to the interfacial deformation. These structures are periodically deformed in a non reciprocal way using magnetic fields, which leads to controllable low Reynolds number locomotion. Such microswimmers provide a basis for micromanipulation applications such as transport of micro-objects, local mixing of fluids or surface cleaning. [less ▲]

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See detailWaveguides for walking droplets
Filoux, Boris ULg; Hubert, Maxime ULg; Schlagheck, Peter ULg et al

E-print/Working paper (2016)

When gently placing a droplet onto a vertically vibrated bath, a drop can bounce without coalescing. Upon increasing the forcing acceleration, the droplet is propelled by the wave it generates and becomes ... [more ▼]

When gently placing a droplet onto a vertically vibrated bath, a drop can bounce without coalescing. Upon increasing the forcing acceleration, the droplet is propelled by the wave it generates and becomes a walker with a well defined speed. We investigate the confinement of a walker in different rectangular cavities, used as waveguides for the Faraday waves emitted by successive droplet bounces. By studying the walker velocities, we discover that 1d confinement is optimal for narrow channels of width of D≃1.5λF. We also propose an analogy with waveguide models based on the observation of the Faraday instability within the channels. [less ▲]

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See detailStatics and dynamics of magnetocapillary bonds
Lagubeau, Guillaume; Grosjean, Galien ULg; Darras, Alexis ULg et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2016), 93

When ferromagnetic particles are suspended at an interface under magnetic fields, dipole-dipole interactions compete with capillary attraction. This combination of forces has recently given promising ... [more ▼]

When ferromagnetic particles are suspended at an interface under magnetic fields, dipole-dipole interactions compete with capillary attraction. This combination of forces has recently given promising results towards controllable self-assemblies as well as low-Reynolds-number swimming systems. The elementary unit of these assemblies is a pair of particles. Although equilibrium properties of this interaction are well described, the dynamics remain unclear. In this paper, the properties of magnetocapillary bonds are determined by probing them with magnetic perturbations. Two deformation modes are evidenced and discussed. These modes exhibit resonances whose frequencies can be detuned to generate nonreciprocal motion. A model is proposed that can become the basis for elaborate collective behaviors. [less ▲]

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See detailScattering theory of walking droplets in the presence of obstacles
Dubertrand, Rémy ULg; Hubert, Maxime ULg; Schlagheck, Peter ULg et al

E-print/Working paper (2016)

We aim to describe a droplet bouncing on a vibrating bath. Due to Faraday instability a surface wave is created at each bounce and serves as a pilot wave of the droplet. This leads to so called walking ... [more ▼]

We aim to describe a droplet bouncing on a vibrating bath. Due to Faraday instability a surface wave is created at each bounce and serves as a pilot wave of the droplet. This leads to so called walking droplets or walkers. Since the seminal experiment by {\it Couder et al} [Phys. Rev. Lett. {\bf 97}, 154101 (2006)] there have been many attempts to accurately reproduce the experimental results. Here we present a simple and highly versatile model inspired from quantum mechanics. We propose to describe the trajectories of a walker using a Green function approach. The Green function is related to Helmholtz equation with Neumann boundary conditions on the obstacle(s) and outgoing conditions at infinity. For a single slit geometry our model is exactly solvable and reproduces some general features observed experimentally. It stands for a promising candidate to account for the presence of any boundaries in the walkers'dynamics. [less ▲]

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See detailFloating self-assembled microswimmers
Grosjean, Galien ULg; Vandewalle, Nicolas ULg; Hubert, Maxime ULg et al

Conference (2016, January 28)

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See detailRotation of melting ice disks due to melt fluid flow
Dorbolo, Stéphane ULg; adami, nicolas; Dubois, Charles ULg et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2016)

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See detailDisplacement of an Electrically Charged Drop on a Vibrating Bath
Brandenbourger, Martin ULg; Vandewalle, Nicolas ULg; Dorbolo, Stéphane ULg

in Physical Review Letters (2016), 116

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See detailRemote control of self-assembled microswimmers
Grosjean, Galien ULg; Lagubeau, Guillaume ULg; Darras, Alexis ULg et al

in Scientific Reports (2015)

Floating magnetic particles can self-assemble into structures. These structures are periodically deformed in a non reciprocal way using magnetic fields, which leads to controllable low Reynolds number ... [more ▼]

Floating magnetic particles can self-assemble into structures. These structures are periodically deformed in a non reciprocal way using magnetic fields, which leads to controllable low Reynolds number locomotion. [less ▲]

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See detailQuantitatively mimicking wet colloidal suspensions with dry granular media
Messina, René; Aljawhari, Sarah; Bécu, Lydiane et al

in Scientific Reports (2015)

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 ... [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. [less ▲]

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See detailComplex Magnetocapillary Microswimmers
Grosjean, Galien ULg; Vandewalle, Nicolas ULg; Lagubeau, Guillaume ULg et al

Poster (2015, July)

When particles are suspended at air-water interfaces in the presence of a vertical magnetic field, dipole-dipole repulsion competes with capillary attraction. Magnetocapillary self-assemblies, composed of ... [more ▼]

When particles are suspended at air-water interfaces in the presence of a vertical magnetic field, dipole-dipole repulsion competes with capillary attraction. Magnetocapillary self-assemblies, composed of N soft-ferromagnetic beads, have been studied as a way to produce controllable micro swimmers at low Reynolds numbers. We hereby investigate the different dynamical behaviors obtained for various self-assemblies. The dynamic interaction of a pair of particles (N = 2) generates a rich behavior at the origin of a non-reciprocal motion, being the major physical ingredient for low Reynolds locomotion. By adding particles to this elementary system up to N = 8, we create new symmetries relevant to generate translational and rotational motions. We propose a model for describing the motion driven by an external field, being the basis for developing elaborated collective behaviors. [less ▲]

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See detailCompound droplet manipulations on fiber arrays
Weyer, Floriane ULg; Lismont, Marjorie ULg; Dreesen, Laurent ULg et al

in Soft Matter (2015), 11

Recent works demonstrated that fiber arrays may constitute new means of designing open digital microfluidic systems. Various processes, such as droplet motion, fragmentation, trapping, release, mixing and ... [more ▼]

Recent works demonstrated that fiber arrays may constitute new means of designing open digital microfluidic systems. Various processes, such as droplet motion, fragmentation, trapping, release, mixing and encapsulation, may be achieved on fiber arrays. However, handling a large number of tiny droplets resulting from the mixing of several liquid components is required for developing microreactors, smart sensors or microemulsifying drugs. Here, we show that the manipulation of tiny droplets onto fiber networks allows for creating compound droplets with a high complexity level. Moreover, this cost-effective and adjustable method may also be implemented with optical fibers in order to develop fluorescence-based biosensor. [less ▲]

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See detailCompound Droplets on Fibers
Weyer, Floriane ULg; Ben Said, Marouen; Hötzer, Johannes et al

in Langmuir (2015), 31(28), 77997805

Droplets on fibers have been extensively studied in the recent years. Although the equilibrium shapes of simple droplets on fibers are well established, the situation becomes more complex for compound ... [more ▼]

Droplets on fibers have been extensively studied in the recent years. Although the equilibrium shapes of simple droplets on fibers are well established, the situation becomes more complex for compound fluidic systems. Through experimental and numerical investigations, we show herein that compound droplets can be formed on fibers and that they adopt specific geometries. We focus on the various contact lines formed at the meeting of the different phases and we study their equilibrium state. It appears that, depending on the surface tensions, the triple contact lines can remain separate or merge together and form quadruple lines. The nature of the contact lines influences the behavior of the compound droplets on fibers. Indeed, both experimental and numerical results show that, during the detachment process, depending on whether the contact lines are triple or quadruple, the characteristic length is the inner droplet radius or the fiber radius. [less ▲]

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See detailBiosensor based on optical fibers
Lismont, Marjorie ULg; Vandewalle, Nicolas ULg; Joris, Bernard ULg et al

Poster (2015, May)

Medical diagnosis and biotechnology progresses are strongly dependent on the development of sensing devices, which, ideally, would allow the reliable detection of very low amounts of biological species in ... [more ▼]

Medical diagnosis and biotechnology progresses are strongly dependent on the development of sensing devices, which, ideally, would allow the reliable detection of very low amounts of biological species in various environments. In addition to these requirements, the detection tools would also be easy to use and would rapidly response. Fluorescent based biosensors fulfil most of these characteristics. In our work, the intersection between two crossed optical fibers is used as the basic unit of an original optical biosensor. As illustrated by figure 1, one optical fiber is used to carry probe molecules and excite fluorescence while the second one is devoted to carry the target species and collect the optical signal arising from the species interacting at the node. The advantages of our set-up over traditional optical sensors are no surface functionalization, use of low amounts of biological species, limitation of the denaturation risk, ease to use and low detection threshold. The developed biosensor is validated on two systems. The first one is a fluorescent calcium indicator, Oregon green 488 BAPTA-2, whose optical emission signal is affected by Ca2+ ions concentration. The second one is based on Rh-Con A and FITC-Dextran complex for which the FRET phenomenon is affected by glucose concentration. In both cases, the results are in agreement with the ones obtained in cuvettes attesting the efficiency of the sensing device. We also show a prototype of a multichannel device composed of multiple crossed optical fibers which are used as species and light carriers. [less ▲]

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See detailRemote control of self-assembled magnetocapillary microswimmers
Grosjean, Galien ULg; Lagubeau, Guillaume ULg; Hubert, Maxime ULg et al

Poster (2015, April)

Physics governing the locomotion of microorganisms and other microsystems is dominated by viscous damping. An effective swimming strategy involves the non-reciprocal and periodic deformations of the ... [more ▼]

Physics governing the locomotion of microorganisms and other microsystems is dominated by viscous damping. An effective swimming strategy involves the non-reciprocal and periodic deformations of the considered body. Herein, we show that a magnetocapillary-driven self-assembly, composed of three soft-ferromagnetic beads, is able to swim along a liquid-air interface when driven by an external magnetic field. Moreover, the system can be fully controled, opening ways to explore low Reynolds number swimming and to create micromanipulators in various applications. [less ▲]

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See detailGranular transport in driven granular gas
Noirhomme, Martial ULg; Opsomer, Eric ULg; Ludewig, François ULg et al

in European Physical Journal E -- Soft Matter (2015), 38

We numerically and theoretically investigate the behavior of a granular gas driven by asymmetric plates. The injection of energy in the dissipative system differs from one side to the opposite one. We ... [more ▼]

We numerically and theoretically investigate the behavior of a granular gas driven by asymmetric plates. The injection of energy in the dissipative system differs from one side to the opposite one. We prove that the dynamical clustering which is expected for such a system is affected by the asymmetry. As a consequence, the cluster position can be fully controlled. This property could lead to various applications in the handling of granular materials in low-gravity environment. Moreover, the dynamical cluster is characterized by natural oscillations which are also captured by a model. These oscillations are mainly related to the cluster size, thus providing an original way to probe the clustering behavior. [less ▲]

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See detailResonant and antiresonant bouncing droplets
Hubert, Maxime ULg; Robert, Damien; Caps, Hervé ULg et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2015), 91

When placed onto a vibrating liquid bath, a droplet may adopt a permanent bouncing behavior, depending on both the forcing frequency and the forcing amplitude. The relationship between the droplet ... [more ▼]

When placed onto a vibrating liquid bath, a droplet may adopt a permanent bouncing behavior, depending on both the forcing frequency and the forcing amplitude. The relationship between the droplet deformations and the bouncing mechanism is studied experimentally and theoretically through an asymmetric and dissipative bouncing spring model. Antiresonance phenomena are evidenced. Experiments and theoretical predictions show that both resonance at specific frequencies and antiresonance at Rayleigh frequencies play crucial roles in the bouncing mechanism. In particular, we show that they could be exploited for bouncing droplet size selection. [less ▲]

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See detailSoft matter: Brittle for breakfast
Vandewalle, Nicolas ULg

in Nature Physics (2015), 11(10), 802-803

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See detailLinking flowability and granulometry of lactose powders
Boschini, Frédéric ULg; Delaval, Vincent ULg; Traina, Karl et al

in International Journal of Pharmaceutics (2015)

The flowing properties of 10 lactose powders commonly used in pharmaceutical industries have been analyzed with three recently improved measurement methods. The first method is based on the heap shape ... [more ▼]

The flowing properties of 10 lactose powders commonly used in pharmaceutical industries have been analyzed with three recently improved measurement methods. The first method is based on the heap shape measurement. This straightforward measurement method provides two physical parameters (angle of repose αr and static cohesive index σr) allowing to make a first screening of the powder properties. The second method allows to estimate the rheological properties of a powder by analyzing the powder flow in a rotating drum. This more advanced method gives a large set of physical parameters (flowing angle αf, dynamic cohesive index σf, angle of first avalanche αa and powder aeration %ae) leading to deeper interpretations. The third method is an improvement of the classical bulk and tapped density measurements. In addition to the improvement of the measurement precision, the densification dynamics of the powder bulk submitted to taps is analyzed. The link between the macroscopic physical parameters obtained with these methods and the powder granulometry is analyzed. Moreover, the correlations between the different flowability indexes are discussed. Finally, the link between grain shape and flowability is discussed qualitatively. [less ▲]

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