Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5-Seeded Growth) - 10.21.14
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The systematic control of crystal growth in microgravity gives insight into the physical laws by which matter organizes itself. The Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5- SeededGrowth) experiment studies how the “rules” for the crystallization of microscopic particles (known as colloids) suspended in liquid change when seed particles are present. These experiments are anticipated to have application to the development of new smart materials.
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ZIN Technologies Incorporated, Cleveland, OH, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
March 2009 - March 2013
Previous ISS Missions
The predecessors to BCAT-5, which are BCAT-3 and BCAT-4 are in operation on the ISS.
- The suspended microscopic particles (or colloids) used in this experiment are an excellent model for atoms. They have the advantages that they are big enough to interact with visible light, which allows us see what’s happening, and big enough to slow down natural processes such as crystallization, allowing us to watch the formation of structures.
- On Earth, gravity interferes substantially with crystallization processes making performing these experiments in microgravity essential for their success.
- A good deal of the behavior of these systems is governed by their entropy. This is related to the presence of seed particles. The driving force toward ordering, while small, may be enhanced and the system may present a unique way to study glassy dynamics in a "monodisperse" suspension when seed particles are present. This sample may help us understand how to control the size of crystals and understand why monodisperse samples which are glass-like on earth crystallize in microgravity.
- The experimental results obtained in microgravity should be very helpful in directing future computational modeling of crystal formation and will provide the experimental input that is critical for forming and testing new models.
- An improved understanding of how crystals form from one another will lead to more improved manufacturing processes and commercial products.
The Binary Colloidal Alloy Test - 5 (BCAT-5) hardware supports four investigations. Samples 1 - 5, the Binary Colloidal Alloy Test - 5: Phase Separation (BCAT-5-PhaseSep) will study collapse (phase separation rates that impact product shelf-life). In microgravity the physics of collapse is not masked by being reduced to a simple top and bottom phase as it is on Earth. Samples 6 - 8, Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) will study the competition between phase separation and crystallization, which is important in the manufacture of plastics and other materials. Sample 9, Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5-SeededGrowth) will study the properties of concentrated systems of small particles when 99.8 percent are identical 0.36 diameter micron spheres and 0.2 percent are 4.14 microns in diameter (11.5X larger); these seed particles may cause heterogeneous crystal growth. Sample 10, Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3D-Melt) will look at the mechanisms of crystal formation and 3-dimensional melting using colloidal particles that change size with temperature.
For the SeededGrowth Sample (9), plans are to experimentally explore the theoretical prediction that the use of seed particles can be used as a way to control the size of crystallites. The control of crystallite size is important in many industrial processes. By introducing the right size and concentration of 'nano-dirt', we use this experiment to record the effect of large (11.5X) spherical seed particles on crystallization. Small nuclei grow on the seed and as they grow, the presence of a larger curved substrate makes it difficult to maintain an unstrained structure. At some stage, the precritical nuclei break away from the surface, and the critical nucleus is only formed in the bulk. The seed particles are identical to the smaller PMMA spheres, including the thin polymeric steric layer attached to the particle surfaces.
The ability to control the size of crystals in the manufacturing stage gives final materials with better performance characteristics such as having a longer shelf life, or tougher and stronger products both for earth and space use.
Scientists believe that larger seed particles introduced into a colloidal mixture influence how the colloids crystallize. This means certain sizes of seed particles may be used to control the size of crystals. The BCAT-5- SeededGrowth experiment assists the development of computer models that predict crystal formation, thus improving the manufacturing of ceramics, composite materials, optical filters and other smart materials.
The BCAT-5 experiment consists of ten small samples of colloidal particles. The ten BCAT-5 samples are contained within a small case the size of a school textbook. The experiment requires a crewmember to set up on a handrail/seat track configuration, ISS Laptop and utilize EarthKAM software to take digital photographs of Samples 1 - 8 at close range using the onboard Kodak DCS760 or Nikon D2Xs camera. Camera Control Files for running the EarthKAM software can be uploaded from Earth to control the photography intervals (how many photographs per hour) and spans (run for how many days) once it is running. Samples 9 - 10 (and possibly some of sample 6 - 8), which may form crystals, require manual photographs (at least initially) be taken by a crewmember. The pictures are down-linked to investigators on the ground for analysis.
A crewmember sets up the video camera and BCAT-5 hardware (Slow Growth Sample Module, Kodak DCS760 or Nikon D2Xs camera, pen-light source, flash and SSC Laptop with EarthKAM software) on a seat track setup to document the BCAT-5 operations as performed on-board the ISS. The crewmember homogenizes (mixes) the sample(s) and takes the first photographs manually. This helps them optimize the setup and shows that the samples were initially fully homogenized when publishing results later. The EarthKAM software automates the rest of the photography session over a period of a few days to a few weeks. The crewmember performs a daily status check once a day (when time is available) to assure proper alignment and focus. At the completion of the run, the crewmember tears down and stows all hardware.
Ground Based Results Publications
Cacciuto A, Auer S, Frenkel D. Onset of heterogeneous crystal nucleation in colloidal suspensions. Nature. 2004; 428: 404-406.
de Villeneuve VW, Dullens RP, Aarts DG, Groeneveld E, Scherff JH, Kegel WK, Lekkerkerker HN. Colloidal Hard-Sphere Crystal Growth Frustrated by Large Spherical Impurities. Science. 2005; 309: 1231-1233.
ISS Research Project-5-SeededGrowth
NIH BioMed-ISS Meeting Video Presentation, 2009—BCAT-5-SeededGrowth
NIH BioMed-ISS Meeting, 2009—BCAT-5-SeededGrowth
NASA Image: ISS016E027863 - Astronaut Dan Tani photographing the BCAT-3 Sample Module using his own design for a ceiling mount in Node 2 of the International Space Station. Great high contrast pictures of difficult-to-capture images resulted from using this setup (February 2008).
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NASA Image: ISS025E008239 - NASA astronaut Shannon Walker, Expedition 25 flight engineer, uses a digital still camera to photograph Binary Colloidal Alloy Test-5 (BCAT-5) experiment samples in the Kibo laboratory of the International Space Station.
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