Colloids are simply fine particles of solids, liquids, or gases suspended in a fluid. And you can find colloidal systems almost everywhere in nature and in industrial processes, such as in butter, milk, aerosols or paints. All of these substances are examples of colloidal dispersions or suspensions. But that's on Earth. In space, where there is no gravity, they start to behave as slow atoms. This is why several experiments are under progress aboard the International Space Station (ISS). According to NASA's Glenn Research Center, the goal is to reach "the supercritical region, where the liquid and gas are no longer distinct states, but rather form a homogeneous supercritical fluid." And if these experiments are successful, they could lead to new technologies, such as computers operating on light instead of electricity.
The NASA news release is particularly focused on photographs taken by the astronauts on the ISS, which are obviously necessary because the scientists behind the experiments are in their labs. And the astronauts have been busy taking pictures of the Binary Colloidal Alloy Test-3 (BCAT-3).
Below are some sample results from BCAT-3 on ISS. "The images are arranged from top to bottom in order of increasing phase separation times (from fastest to slowest)." Only the three samples which exhibited phase separation are shown here (Credit: NASA).
You'll find more details about these results on this page.
Those colloidal / polymer mixtures near the critical point are already starting to phase separate into two components, a colloid rich phase (blue) and a colloid poor phase (black). You can tell by eye how much the sample has phase separated by simply seeing the width of the continuous blue region: it coarsens and grows as the phase separation proceeds. It looks like we're actually able to visualize this phase separation in microgravity from the beginning.
Now, why is this important to reach this supercritical point?
Supercritical carbon dioxide is used to extract molecules from plants for pharmaceuticals. Supercritical water is used to remove toxic waste from contaminated soil. And some scientists believe supercritical fluids could be used to extract magnesium from rocks on Mars to make rocket fuel.
Will these experiments in space benefit us on Earth? The researchers think so.
According to the BCAT-3 scientists, studying colloids in space could lead to revolutionary advances in technology, such as computers that operate on light, new pharmaceuticals, clean power sources and unique propellants for rocket engines.
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Sources: NASA's Glenn Research Center news release, October 3, 2005; and various web sites
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