The ESA ‘Spin Your Thesis!’ programme gives university students the opportunity to perform a scientific or technology experiment which is linked to their project, by participating in a centrifuge campaign that provides hypergravity conditions. The experiments are carried out in the ESA Large Diameter Centrifuge facility at ESTEC in Noordwijk, the Netherlands.
Our PhD students have been selected for their project on Leidenfrost droplets !
See the ESA web pages.
The website dedicated to our project “QUANDROPS” (2012-2017) is now open. This project aims to study the particle-wave association of bouncing droplets. In recent experiments, such droplets have indeed displayed a number of surprising analogies with quantum particles, including tunneling and double-slit interference. Those droplets can therefore be considered as a classical manifestation of quantum wave-particle duality in the spirit of Bohm’s interpretation of quantum mechanics.
Please also note the beautiful logo of this new project !
We investigated the dynamics of a vertical column of 12 beads submitted to a series of taps. Impulses are strong enough to eject beads. The motion of the beads are recorded using a high-speed camera. Depending on the frequency of taps, complex trajectories are obtained as illustrated in the front picture. The trajectories are analyzed in our last article .
For low tap frequencies, the pulses travel through the pile and expel a few beads from the surface. After a few bounces, the system relaxes to the chain of contacting grains. When the tap frequency increases, fluidization is obtained. In the fluidized part of the pile, adjacent beads are bouncing in opposition of phase (see top picture). This phase locking of the top beads is observed even when the bottom beads experience chaotic motions. While the mechanical energy increases monotically with the bead vertical position, heterogeneous patterns in the kinetic energy distribution are found when the system becomes fluidized.
 G. Lumay, S. Dorbolo, O. Gerasymov and N. Vandewalle, Experimental study of a vertical column of grains submitted to a series of impulses, Eur. Phys. J. E 36 , 16 (2013) – PDF
Locomotion at low Reynolds number is a key physical mechanism  for microscopic living organisms, but has lots of technological applications like nanomachines and microrobots . Our last paper  proposes a tricky experiment for generating low Reynolds swimming of microscopic particles along a liquid-air interface.
First, identical soft ferromagnetic particles are placed on a liquid-air interface. Capillary attraction is prevented by applying a vertical magnetic field which provides a repulsive interaction between the particles. The balance of capillary attraction and magnetic repulsion creates a self-assembly  as shown in the front picture. These structures are then perturbed by applying an oscillating horizontal field. The resulting cooperative dance of the particles provides a net propulsion of the particles along the liquid surface (see trajectories on the picture below). The self-assembly is swimming ! See the movies below :
- Movie 1 - An efficient swimmer of N=3 beads.
- Movie 2 - The horizontal field is switched off. The swimmer is seen to stop its motion. Then the field is switched on but in another direction. The motion resumes but in a different pulsating mode (with a different swimming speed).
- Movie 3 - The complex motion of a swimming (pentagonal) assembly made of N=6 beads.
This work opens new perspectives in mesoscopic physics. The most important feature of our system is that both self-assembling and periodic deformations can be rescaled to smaller sizes.
 E.Lauga, Soft Matter 7, 3060 (2011)
 P.Tierno, R.Golestanian, I.Pagonabarraga, and F.Sagués, Phys. Rev. Lett. 101, 218304 (2008)
 G.Lumay, N.Obara, F.Weyer, N.Vandewalle, Soft Matter 9, 2420 (2013) - PDF
 N.Vandewalle et al., Phys. Rev. E 85, 041402 (2012) - PDF - Post
Foams are common fluid entities of our everyday life. Our group is, among others, involved in ESA projects on the foam generation and stability under microgravity . On Earth, the gravitational drainage dries the foam such that an interface between the foam and the liquid pool is observed.
In a recent paper , the dynamics of this foam/liquid interface has been investigated. The idea of this research is to see this interface as a separation between two fluids, characterized by a given (effective) surface tension. By vertically shaking the system, the forcing acceleration faces this effective surface tension and, above a critical threshold, causes the emergence of Faraday waves. Different threshold values have been observed as a function of the foam properties. A phenomenological model has been proposed.
 N.Vandewalle, H.Caps, G.Delon, A.Saint-Jalmes, E.Rio, L.Saulnier, M.Adler, A.L.Biance, O.Pitois, S.Cohen-Addad, R.Hohler, D.Weaire, S.Hutzler, D.Langevin, Foam Stability in Microgravity, J. Phys. Conf. Series 327, 012024 (2011) – PDF
 A.Bronfort and H.Caps, Phys. Rev. E 86, 066313 (2012) – PDF