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Sept. 3, 2020
Toothpaste, 3D printing, pharmaceuticals, and detecting shifting sands on Mars may not seem related to each other at all. Yet each stands to benefit from improvements made thanks to years of research on colloids aboard the International Space Station.
Mixtures of tiny particles suspended in a liquid, colloids occur in many forms. These include natural mixtures such as milk and muddy water as well as a range of manufactured products from shampoo to medicine to salad dressing. Some colloids contain unique particles capable of forming crystals that assemble into new materials.
Image above: NASA astronaut Jessica Meir configures the Light Microscopy Module (LMM) for Advanced Colloids Experiment-Temperature-4 (ACE-T-4), which examines the transition of an ordered crystal to a disordered glass to determine how increasing disorder affects structural and dynamic properties. Image Credit: NASA.
Humans have continuously lived and worked aboard the space station for nearly 20 years. Researchers have used the orbiting lab for almost that long to better understand the behavior of colloids – both to improve products used in our everyday lives and create entirely new ones, including some that could enable exploration farther into space. These experiments have advanced understanding of basic physics as well.
Studying colloids on Earth is complicated by gravity, which causes some particles to rise and others to sink. Microgravity takes away that complication and makes possible research that can help companies design better products. Procter & Gamble (P&G) researcher Matthew Lynch says the basic research is of interest to the academic community as well. For example, the relationship between the shapes of particles and how they interact contributes to the creation of new materials.
Image above: Canadian Space Agency (CSA) astronaut Chris Hadfield sets up Binary Colloidal Alloy Test (BCAT) Session 1 during Expedition 34. Image Credit: NASA.
The long list of colloid research on the space station includes Binary Colloidal Alloy Tests (BCAT), a series of more than 40 experiments that began in 2004. Many BCAT experiments looked at phase separation, the point at which a mixture separates, which plays a role in product quality and shelf life.
The list also includes ongoing Advanced Colloid Experiments (ACE), with more than a dozen investigations to date. The ACE series has examined the behavior of different types of particles and how different conditions affect the way particles form 3D crystals. Understanding this process and learning to control it could improve 3D printing, for example, and make possible the creation of advanced optical materials.
Image above: NASA astronaut Karen Nyberg works on an Advanced Colloids Experiment (ACE) investigation to help researchers understand how to optimize stabilizers and extend the shelf life of products like laundry detergent, paint, and ketchup. Image Credit: NASA.
ACE research also tackled a basic challenge: how to keep a product liquid enough to dispense easily and yet prevent ingredients, or particles, from clumping together and settling. That process, called coarsening, turns a creamy shampoo into a layer of gooey solids and watery liquid.
“It is easy enough to do one or the other,” Lynch says. “I could suspend something in concrete and it would stay suspended, but then the product has to somehow dispense. Doing both is not a trivial problem.”
Some two-thirds of P&G’s biggest brands could benefit from colloids research, according to Lynch, and space station research has contributed to three new patents for the company. With annual sales for its Downy fabric softener alone totaling about $4 billion, Lynch points out that even a one percent savings in production costs or a slightly longer shelf life becomes significant. Long-term space exploration, such as a years-long trip to Mars, stands to benefit from extended product shelf-life as well.
Better 3D printing or additive manufacturing also is a capability critical for future long-term space missions.
NASA Takes First 3-D Microscopic Image on the Space Station
Video above: A composite 3-D model of NASA's Advanced Colloids Experiment (ACE). Video Credits: P&G, NASA, ISS National Lab.
“On a long space voyage, an engine part will fail, and you might not take along a spare,” says Paul Chaikin, a physics professor at New York University and principal investigator on several ACE investigations. Understanding how particle shape, size, and packing behavior affect this process is key to using colloids in additive manufacturing to make those spare parts.
The work also explores the feasibility of creating particles that come together on their own, using different forms of energy to instruct the particles exactly how to bind together so they create materials with specific properties. Future explorers could take along these particles as the building blocks to make almost anything they need.
Colloid research aboard the orbiting laboratory also helped scientists develop a technique using light scattering to observe how particles stick together to form rigid networks. This technique can reveal properties of the surface of a planet as well, possibly detecting landslides on Mars, for example. In addition, it could help predict structural failure of roads and bridges and even earthquakes.
The addition of a confocal microscope in the station’s Light Microscopy Module (LMM) in 2009 greatly enhanced colloid research. With a conventional microscope, light travels as far into a specimen as it can penetrate. A confocal microscope focuses a beam of light at one narrow slice of a specimen at a time, capturing multiple 2D images that can then be used to create a 3D structure.
International Space Station (ISS). Animation Credit: NASA
“The confocal capability is critical,” Lynch says. “Without it, you can see the colloids, but you get no depth, and it is very difficult to pull out the physics. LMM has the resolution to identify where things are and the dynamics of the system.”
All of these advances would have been much more difficult, if not impossible, without access to the space station.
“A lot of our understanding of colloids came from these experiments in microgravity,” Chaikin says. “Getting rid of gravity was really important in allowing us to isolate different effects. It essentially made this field.”
NASA’s Glenn Research Center in Cleveland oversees both BCAT and ACE, and the ISS U.S. National Lab has sponsored several individual investigations. The Biological and Physical Sciences (BPS) Division of NASA’s Science Mission Directorate at NASA Headquarters in Washington also sponsors ACE investigations as part of its mission to conduct fundamental science.
Related links:
Binary Colloidal Alloy Tests (BCAT): https://www1.grc.nasa.gov/space/iss-research/mwa/bcat/
Advanced Colloid Experiments (ACE): https://www1.grc.nasa.gov/space/iss-research/iss-fcf/fir/lmm/ace/
Light Microscopy Module (LMM): https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Facility.html?#id=531
Biological and Physical Sciences (BPS): https://science.nasa.gov/biological-physical
ISS National Lab: https://www.issnationallab.org/
Spot the Station: https://spotthestation.nasa.gov/
Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/overview.html
International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html
Images (mentioned), Animation (mentioned), Video (mentioned), Text, Credits: NASA/Michael Johnson/JSC/International Space Station Program Research Office/Melissa Gaskill.
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