FSL Soft Matter Dynamics – Foam Optics and Mechanics (FOAM)

The Foam Optics and Mechanics (FOAM) investigation studies the relative stability of foams and bubbly liquids in order to gain insight into how they evolve with time. This investigation will study how they evolve through a combination of gas diffusion across film separating neighboring bubbles, direct coalescence via film rupture, and liquid flow between bubbles. There is some level of understanding for very dry foams and for wet froths, however, the crucial intermediate regime of wet foams and bubbly liquids is unknown due to the confounding presence of gravitational drainage on earth. By studying the stability of foams and bubbly liquids in microgravity, the rearrangement dynamics of bubbles will be characterized as fundamental to understanding the mechanics of flow and stress relaxation.

Batch-3 sample carousel was delivered to the International Space Station via Northrop Grumman Commercial Resupply Services Mission 17.

The Foam Optics and Mechanics (FOAM) investigation aims to understand how foams and bubbly liquids evolve in microgravity conditions. Aqueous foams consist of gas bubbles dispersed in a continuous volume of liquid containing active surface molecules that retard or prevent direct coalescence. Even though foams can support shear stress statically like an elastic solid, over time, the gas and liquid phases separate, and understanding the degree of stability is crucial to control applications that will allow humans to thrive in deep space. The Soft Matter Dynamics experimental container was designed in collaboration with ESA and European foam researchers to create foams in situ and to use multiple light scattering and optical imaging diagnostics to quantify bubble sizes, shapes, positions, and rearrangement dynamics and how they evolve over a long period of time. The flexibility of this apparatus is enabling microgravity study of granular (COMPGRAN) and emulsion (PASTA) samples.

The proposed experiments will provide fundamental guidance for how to control the flow and separation of bubble-laden liquids. Advancing our knowledge is crucial for developing a recovery and recycling apparatus for the closed-loop processing of water aboard future Mars-bound spacecraft. Recovered water will be contaminated with both gas bubbles and surface-active chemicals, therefore, robust foams and bubbly liquids would be created. These foams and bubbly liquids must be pumped around, and the gas must be separated from the liquid. Furthermore, foams are useful for fire-suppression. In addition to supporting human health and safety, the proposed experiments will provide fundamental guidance for how to produce synthetic cellular solids and metallic foams. Such knowledge is crucial for developing on-board fabrication facilities in order to reduce upload mass and volume.

Foams are found in nature as well as industries ranging from food and cosmetics to paper, petroleum, and mining. They also arise unwanted in processing multicomponent liquids and are precursors to synthetic polymeric and metallic cellular solids. Understanding their stability and mechanics is crucial in all cases for controlling behavior and for creating sustainable, more efficient processes and improved materials. Furthermore, in terms of the environment, the presence of foams in natural or recycled waters signals the presence of surface-active impurities and a need for clean-up, which in turn can be facilitated by injecting air and skimming off the resulting foam.