Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) - 07.22.14
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Science Objectives for Everyone
The Binary Colloidal Alloy Test 5 - Compete (BCAT-5-Compete) experiment studies how colloids, which are small particles suspended in a liquid, crystallize and separate from the liquid. Crewmembers take high-resolution photographs of the colloidal particles as they clump together. The experiment looks at the competition between crystallization and phase separation, which is important in the manufacturing of plastics as well as many other products.
Science Results for Everyone
Station crewmembers photographed various mixtures of colloids, small particles suspended in a liquid, to see whether the particle's crystallize affects the way they separate from the liquid and vice versa. The images showed a unique “crystal gel’’ occurring when separation stopped, apparently because stiffness of the crystalline strands exceeds the surface tension between the liquid and gas. In microgravity, small surface forces play a major role in crystallization, while on Earth, gravity overwhelms these forces and interferes with crystallization. Better understanding of how crystals form and colloids separate will help improve manufacturing processes.
ZIN Technologies Incorporated, Cleveland, OH, United States
Sponsoring Space Agency
Canadian Space Agency (CSA)
ISS Expedition Duration
March 2009 - March 2011
Previous ISS Missions
The predecessors to BCAT-5, are BCAT-3 and BCAT-4, which are in operation on the ISS.
- The 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 going on, 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.
- An improved understanding of how crystals form and how solids and liquids separate 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% are identical 0.36 diameter micron spheres and 0.2% 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.
The BCAT-5-Compete samples consist of colloids suspended in solvent with added polymer. The polymer allows scientists to adjust the particle interactions though depletion attraction (for example, if the polymers are pushing on all sides of the colloidal particles in solution and two particles touch or one comes close to a wall, the polymers are no longer pushing on all sides and this models attraction). By changing the amount of colloid and the relative amount of colloid and polymer, the equilibrium state of the sample can be changed. The BCAT-5-Compete samples will have equilibrium concentrations that result in mixtures of colloid-liquids, colloidal gas, and colloidal crystal. The purpose of these experiments is to study the kinetics that lead to these unique solutions.
The samples will be mixed (thoroughly randomized) and are expected to take several days to reach a nearly equilibrium state. During this time the EarthKAM system will be used to take high-resolution photographs of the samples at regular intervals. As the phase separation/crystallization kinetics begins immediately after the samples are mixed, the interval between images should be relatively short. As the kinetics proceed, the time between images can be increased. Imaging such as this has been performed during BCAT-3 and BCAT-4. The downlinked images will be analyzed using standard techniques to measure the spatial size of concentration variations in the sample or sizes of crystallites as a function of time.
Because crystals may be present, the BCAT-5-Compete samples will likely require that a small flashlight be used to determine optimal lighting and camera position. Once this is determined, the experiment can proceed using the EarthKAM software to control the camera to make a movie of the crystal formation process in an effort to record information about the time dependence of crystal formation.
Ultimately, the experiment is designed to determine if in samples that both phase separate and crystallize, if the dynamics of either process is affected by the other. For example, one possible scenario might be that phase separation, which induces local density increases, reduces the crystallite initiation time because of the increased density. These systems are relatively unexamined and a wealth of new phenomena may be observed.
Microgravity is essential for colloid crystallization research, because gravity greatly interferes with crystal formation. The experiment looks to answer basic physics questions that could be applied to colloidal products used in the space program, including food and consumable products.
The experiment determines how crystallization and the separation between the solid and the liquid phases affect one other. For instance, colloids separating out of their liquid suspension increases the density of small particles, which could make the particles crystallize faster. Competition between these two processes can cause defects in colloid-based manufacturing, such as the production of plastics. Understanding these processes helps industrial manufacturers make better products.
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 it up on the Maintenance Work Area (MWA) or on a handrail/seat track configuration, along with an ISS Laptop that will utilize EarthKAM software to take digital photographs of Samples 1 - 10 at close range using the onboard Kodak DCS760 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 6 - 10, which may form crystals, require manual photographs to be taken (at least initially) by a crewmember. The pictures are downlinked to investigators on the ground for analysis.
A crewmember sets up the video camera and BCAT-5 hardware (Slow Growth Sample Module, DCS760 Camera, pen-light source, flash and SSC Laptop with EarthKAM software) in the Maintenance Work Area (MWA) 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 that ranges from 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.
Sabin J, Bailey AE, Espinosa G, Frisken B. Crystal-Arrested Phase Separation. Physical Review Letters. 2012 November 9; 109(19): 195701 (5).
Ground Based Results Publications
Cheng Z, Chaikin PM, Zhu J, Russel WB, Meyer WV. Crystallization Kinetics of Hard Spheres in Microgravity in the Coexistence Regime: Interactions between Growing Crystallites. Physical Review Letters. 2002; 88(1): 015501-1 - 015501-4. DOI: 10.1103/PhysRevLett.88.015501. PMID: 11800960.
de Hoog E, Kegel WK, van Blaaderen A, Lekkerkerker HN. Direct observation of crystallization and aggregation in a phase-separating colloid-polymer suspension. Physical Review E. 2001; E.64: 021407.
Cheng Z, Zhu J, Russel WB, Meyer WV, Chaikin PM. Colloidal hard-sphere crystallization kinetics in microgravity and normal gravity. Applied Optics. 2001; 40(24): 4146-4151. DOI: 10.1364/AO.40.004146.
Lu PJ, Lu PJ, Zaccarelli E, Ciulla F, Schofield AB, Sciortino F, Weitz DA. Gelation of particles with short-range attraction. Nature. 2008; 453: 499-503. DOI: 10.1038/nature06931.
ISS Research Project-BCAT-5-Compete
Canadian Space Agency - Binary Colloidal Alloy Test - 5
Experimental Soft Condensed Matter Group
NIH BioMed-ISS Meeting Video Presentation, 2009—BCAT-5-Compete
NIH BioMed-ISS Meeting, 2009—BCAT-5-Compete
NASA Image: ISS016E027863 - Astronaut Dan Tani took this photograph of 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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Image of BCAT-5-Compete sample 7 that was taken on GMT 283. Sample 7 is one of the samples being used to study the competition between phase separation and crystallization in colloidal samples. This photo shows distinct phase separation arrested by crystal growth. Image courtesy of Glenn Research Center.
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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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