FOAM-C (COARSENING OF WET FOAMS)
Laboratories : LPS (Univ. Paris-Saclay), INS Paris (Sorbonne Univ.), Univ. Eiffel Marne la Vallée
Foams are dispersions of gas bubbles in liquids. They evolve rapidly on ground due to gravity-driven drainage. Microgravity suppresses drainage and allows studying wet foams, containing a substantial and controllable amount of liquid, while on ground one is usually limited to dry foams, with liquid fractions smaller than a few percent.
A project called Foam-C, where C stands for coarsening, has been approved by ESA. Coarsening is an ubiquitous phenomenon in phase separations. It is widely observed in alloys, polymers, emulsions, foams and even in biological systems. However, coarsening of materials where the two phases have comparable volume fractions is still poorly understood.
The experiments in the ISS began in March 2020 and have been so far successful. Among the many new observed phenomena, we found that coarsening naturally produces hierarchical bubble size distributions. Foaming being a generic method to produce solid cellular materials with many applications, this opens up a new way of designing hierarchical materials. We also monitored the rearrangements of wet foams structure. These rearrangements also occur during the flow of foams, the topic of a future new project, REFOAM.
Time evolution of the bubbles at the foam cell surface, liquid fraction 38%
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