In the Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) investigation, over time a crewmember photographs microscopic particles (colloids) suspended in a liquid. This experiment investigates the competition between crystallization and the separation of solids from liquids. An improved understanding of these processes will lead to more improved manufacturing processes and commercial products.Principal Investigator(s)
ZIN Technologies Incorporated, Cleveland, OH, United States
Canadian Space Agency (CSA)Sponsoring Organization
Information PendingResearch Benefits
Information PendingISS Expedition Duration:
March 2009 - March 2014Expeditions Assigned
19/20,21/22,25/26,37/38Previous ISS Missions
The predecessors to BCAT-5, are BCAT-3 and BCAT-4, which are in operation on the ISS.
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.
BCAT-5-Compete addresses basic physics questions about how defects form when phase separation and crystallization compete.Earth Applications
These samples will provide important data that is not available on Earth; data which can guide our understanding of crystallization, which impacts production (e.g., when making plastics). Production processes often have defects introduced when there is a competition between processes like phase separation and crystallization. Studying this competition in the absence of gravitational settling should provide insights into how to control it.
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.Operational Protocols
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.
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