Multiphase fluid systems are strongly influenced by gravitational phenomena that affect everything from transport dynamics to the self-assembly of ordered systems. Buoyancy-driven convection drives heat and mass transport, providing a source of mixing. Density-driven segregation leads to inhomogeneities and phase separation including sedimentation. One byproduct of the sedimentation is the occurrence of stratification phenomena in self-assembled multiphase fluid systems such as foams and emulsions. The removal of gravity as a force provides opportunities for the investigation of discrete phenomena such as diffusion or viscosity in isolation. For example, in a persistent microgravity environment, the interfacial energies in self-assembled structures can be studied in isolation from sedimentation and stratification effects.
The International Space Station (ISS) U.S. National Laboratory offers a unique environment in persistent microgravity that enables the decoupling of physical phenomena such as buoyancy-driven convection from diffusion. Areas of investigation onboard the ISS have included droplet formation, colloid interactions (emulsions, nanoparticles, biomolecules, etc.), foam formation and stability, gel formation (aerogels, hydrogels, etc.), and self-assembled structures. For example, microgravity provides the opportunity to study “wet” foams in the absence of drainage—a result that is difficult to replicate terrestrially.
We will introduce the underlying physical phenomena of multiphase liquids in microgravity. We will present case studies of multiphase liquid system investigations conducted onboard the ISS, including studies of droplet formation, gel and foam stability, and the self-assembly of hydrogels and aerogels, and compare results with those from terrestrial experiments. We will also discuss translational lessons learned from microgravity experiments that inform and direct terrestrial research and manufacturing. Finally, we will present opportunities for future microgravity experiments and access to ISS facilities through the ISS U.S. National Laboratory.