The peculiar behavior of granular materials in microgravity is a hard physics problem. In the dilute case, granular gases loose kinetic energy and may form clusters. In order to avoid this “cooling effect”, mechanical energy should be continuously injected in the system. This is exactly the subject of the SpaceGrain project  of the European Space Agency (ESA). It has been proven that a dynamical cluster may appear  for such driven systems.
Our last paper  explores the case of nonequal energy injection in a granular gas, allowing for dynamical cluster motion. It is possible to control the position of a cluster by selecting the right values of the driving parameters. Granular transport becomes therefore possible as shown in the picture.
Applications can be found for exemple in asteroid mining , or in building structures in space.
 E.Opsomer, F.Ludewig, and N.Vandewalle, Dynamical clustering in driven granular gas, EPL 99, 40001 (2012)
 M.Noirhomme, E.Opsomer, N.Vandewalle, F.Ludewig, Granular transport in driven granular gas, Eur. Phys. J. E 38, 9 (2015) – PDF
For the last 11 years and following an original idea of the Nobel Prize Pierre-Gilles de Gennes, the ESPGG has been promoting researchers from Paris and outside by mean of plenary experimental conferences. More than 100 scientists have so presented the results of their studies, performing live experiments.
Last Monday, the GRASP talked about fluids and granular materials. Starting with dry granular materials, water was added drop by drop, evidencing the drastic changes in the physical behavior of the so-generated material.
Soap films are quite familiar objects that can be produced by simply pulling a frame out of a soapy water vessel. Carefully looking at this film reveals a horizontal succession of colored fringes. Those interferences fringes attest to both the existence of a nonuniform thickness profile in the soap film. Mechanically speaking, this implies that the surface tension in the film is non constant in order to counterbalance the weight of the film. This assertion was first proposed by Gibbs in 1878  and pursued by Mysels  and co-workers. However, no experimental evidence for this surface tension gradient has been provided so far.
In a recent paper , we have experimentally investigated the local surface tension in soap films by use of soft deformable objects, giving an experimental proof of early Gibbs’idea.
 J. W. Gibbs, The Collected Works of J. Willard Gibbs (Longmans Green, New York, 1931).
 K. Mysels, K. Shinoda, and S. Frankel, Soap Films (Pergamon, New York, 1959).
 N. Adami and H. Caps, Surface tension profiles in vertical soap films, Phys. Rev. E 91, 013007 (2015) – PDF
This image will be presented in a poster at the Gallery of Fluid Motion (APS DFD, San Fransisco). A sophisticated compound droplet can be created on a fiber array. The picture shows a droplet with four different internal components.