Coarsening dynamics of three-dimensional levitated foams: From wet to dry.

We study diamagnetically levitated foams with widely different liquid fractions. Due to the levitation, drainage is effectively suppressed and the dynamics is driven by the coarsening of the foam bubbles. For dry foams, the bubble size is found to increases as the square root of foam age, as expected from a generalized von Neumann law. At higher liquid content the behavior changes to that of Ostwald ripening where the bubbles grow with the 1/3 power of the age. Using Diffusing Wave Spectroscopy we study the local dynamics in the different regimes and find diffusive behavior for dry foams and kinetic behavior for wet foams.

Influence of gravity on a granular Maxwell's demon experiment.

In the usual description of the granular Maxwell's demon experiment, where phase separation occurs due to an instability in the densities, the control parameter scales linearly with gravity. In this paper we investigate this scaling experimentally using the properties of diamagnetic particles in strong magnetic-field gradients to reduce and even balance gravitation. We find that phase separation occurs even at vanishingly small gravitational accelerations as is predicted by other theories. This is due to the fact that granular samples tend to form clusters as a result of the inelasticity of the particle collisions. Combining the heat balance of the driven granular gas with the cooling rate and thus the appearance of clustering, we are able to describe the crossover between the limiting cases.

Experimental investigation of the freely cooling granular gas.

We investigate the dynamics of the freely cooling granular gas. For this purpose we diamagnetically levitate the grains providing a terrestrial milligravity environment. At early times we find good agreement with Haff's law, where the time scale for particle collisions can be determined from independent measurements. At late times, clustering of particles occurs. This can be included in a Haff-like description taking into account the decreasing number of free particles. At very late times, only a single particle determines the dynamics, which is again described by a version of Haff's law. With this a good description of the data is possible over the whole time range.