Are liquids foams unstable on Earth more stable in microgravity conditions ?
Résumé
Liquids that produce stable foams on Earth also produce stable foams in microgravity environments as it could be expected (1). It is less obvious to guess what will happen with liquids that produce small amounts of foam or no foam at all on Earth. Experiments in parabolic flights and in the International Space Station showed that even water can produce significant amount of foams, although only if the liquid volume fraction is higher than about 35%. Ethanol-water mixtures also produce foams in microgravity, the amount being maximum in a range of ethanol volume fraction of 10-20% as on Earth (but the foam volume in microgravity is much larger). Still more unexpected, aqueous surfactant solutions containing antifoam particles (hydrophobic silica, nonionic solutions above the cloud point) produce appreciable amounts of foams in microgravity. All the foams produced in microgravity remain stable over long periods of time. We will explain how we have been able to rationalize these observations.