Advanced Colloids Experiment-Microscopy-2 (ACE-M-2)

Sometimes it's hard to tell a gas from a liquid. Advanced Colloids Experiment-Microscopy-2 (ACE-M-2) observes the microscopic behavior of liquids and gases separating from each other. The investigation examines the behavior of model (colloid rich) liquids and model (colloid poor) gases near the critical point, or the point at which there is no distinct boundary between the two phases. ACE-M-2 uses a new microscope to record micro-scale events on short time scales, while previous experiments observed large-scale behavior over many weeks. Liquids and gases of the same material usually have different densities, so they would behave differently under the influence of gravity, making the microgravity environment of the International Space Station ideal for these experiments.

The experiment has concluded, and science is being evaluated.

Advanced Colloids Experiment-Microscopy-2 (ACE-M-2) investigates the behavior of liquid-gas phase separation near the critical point in a model colloid-polymer system. Colloids are here defined as micron-scale solid particles suspended in a fluid. Particles in this size range are small enough so that thermodynamics drives their behavior (as opposed to larger particles in the granular limit, where they are essentially static over experimental time scales), yet the particles are also large enough to interact with light, and so can be probed with scattering (for example, in the Physics of Colloids in Space (PCS) experiment previously flown in microgravity) and microscopy (the present ACE experiments). As a result, single-particle knowledge can be obtained for a wide variety of physical processes, including crystallization, gelation, phase separation, and dynamical arrest in glasses.

On Earth, gravity plays a big role in how liquids and gases interact: The heavier liquid phase settles beneath a lighter gas phase, and these differences in density enable easy separation. But the flow and behavior of complex fluids and phase separation where there is little or no gravity is not well understood. A greater understanding of liquid-gas interaction in microgravity could benefit a wide range of fluid storage, transport and processing systems for future spacecraft.

Particle separation and behavior in liquids, gels, and creams is important for developing consumer and household products, which are worth billions of dollars annually to the U.S. economy. Many consumer products are complex fluids, combining microscopic particles in gel or liquid, which are similar to the model colloidal system used in the ACE investigations which give insight into product formulations that could be used to maximize stability and shelf life.

Space Station Research Explorer