The GRASP investigates the physical properties of disordered and fluctuating systems such as granular materials and complex fluids. The systems currently under investigations are : antibubbles, compaction of granular systems, bouncing droplets, dense bubble flows, fish tracking, foams in microgravity, ... The group has also developped many activities in physics education.
News
Digital microfluidics on a wire [15/07/2009]
Dew droplets are seen on spider webs in the early morning. Small ones remain pinned on the threads while larger ones slide down the grid, fuse with others, leave some smaller droplets in their wake, and eventually fall from the web. Spontaneous motion, coalescence, and division are words commonly encountered in digital microfluidics, where droplets are used as tiny liquid entities manipulated through complex channel networks.
Is it possible to mimic these arachnidean constructions and to invent fiber-based microfluidic devices ? Some clues in our latest publication in Applied Physics Letters...
Monodisperse foam on a bubble [16/06/2009]
The GRASP has started studying monodisperse foams of washing liquid with a controlled bubble size. These foams were created by using a "T"-junction, the basic element of channel microfluidic. The production of monodisperse foams is interesting in many respects.
a) A big bubble is totally covered with many millimetric bubbles, which allows us to study some problems of topology: how to pave a spherical surface ? We can also observe a humidity gradient in the foam; the dry bubbles (at the top) have a pentagonal or hexagonal shape (like in honey combs) while the wet bubbles (at the bottom) are more spherical.
b) Some horizontal interference fringes are observed; the colors can be related to the thickness gradient of the soap film. Above the fringe pattern, we can see the marginal regeneration due to the drainage of the thin liquid film.
c) This bubble is similar to a magnifying glass; little bubbles appear enlarged.
FRS-FNRS annual meeting in Statistical Physics [22/04/2009]
Next May 18-19, the F.R.S.-FNRS thematic doctoral school Nonlinear physics, complex systems and statistical mechanics holds its annual meeting at the University of Liège (Sart-Tilman). Various seminars are given by belgian and international lecturers. In particular, we are pleased to welcome Martin Van Heck, from Leiden institute of physics. He will tell us about his lastest in a talk entitled Flow of Foams from a Jamming Perspective. A poster session is going to be held, in which one of ours, Eric Mersch, presents An experimental study of cohesive granular flow in silo .
Selected for the Gallery of nonlinear images [27/03/2009]
An oil droplet is known to bounce indefinitely on a vibrated bath. But what happens to a compound droplet (i.e. a droplet made of water surrounded by a layer of oil) in the same conditions ? The GRASP investigated this question, and found a very surprising answer : the bouncing compound droplet quickly transforms into a kind of micro-mayonnaise ! A number of tiny oil droplets are injected inside the water part, as in an emulsion.
Researchers from the GRASP have investigated the dynamics of a "trimer" under vertical vibration. This uncommon object, consisting in three balls linked together (e.g. glued at the corners of a triangle), exhibits a large variety of amazing behaviors such as a combined bouncing/rotating motion.
This work has just been published in the New Journal of Physics, which is freely available online.
