Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) - 12.03.13
Science Objectives for Everyone
Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) studies how crystals form from solid materials suspended in a liquid. Comparing crystals grown in space with those grown on the ground reveals how the forces of gravity influence the creation of these crystalline structures. The experiment serves to improve scientific understanding of important physics processes, including how crystals form in different temperatures and at different particle concentrations in the liquid.
Science Results for Everyone
ZIN Technologies Incorporated, Cleveland, OH, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)Research Benefits
Information PendingISS Expedition Duration:
October 2007 - September 2014Expeditions Assigned
16,17,18,19/20,29/30,31/32,33/34,35/36,37/38,39/40Previous ISS Missions
The predecessors to BCAT-4; BCAT-3 operated on ISS, and BCAT, operated on Mir in 1997 and 1998.
- Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) consists of microscopic spherical particles (known as colloids) of a variety of different diameters (with the same average size) suspended in a liquid.
- The effects of this diversity in diameter among the particles will be studied with respect its affects on crystallization.
- Crewmembers photograph the samples over time to document the way that the particles crystallize in microgravity.
- Results from these experiments help scientists develop fundamental physics concepts which will enable the development of a wide range of new next generation technologies (such as in high speed computers and advanced optical devices).
The Binodal Colloidal Aggregation Test (BCAT) hardware supports four experiments. The first hardware, Binary Colloidal Alloy Test - 3, consisted of three separate investigations, Binary Alloy (BCAT-3-BA), Critical Point (BCAT-3-4-CP) and Surface Crystallization (BCAT-3-SC), which were delivered to the International Space Station (ISS) during expedition 8. The next hardware, BCAT-4, consists of two separate investigations, Critical Point (a continuation of the investigation on BCAT-3) and Polydispersion (BCAT-4-Poly).
The BCAT-4-Poly polydispersed (characterizing the variation in particle size in the dispersed phase) and seeded samples consist of polymethyl methacrylate (PMMA) particles in an index matching decalin/tetralin mixture (the same colloid and solvent materials as the critical-point samples, but at a volume fraction of ~0.59). Although these samples are at or above the so-called glass transition point, colloidal crystals are expected to form. The particle size distribution and the addition of spherical seed particles should affect the free energy barrier for crystal nucleation, that is, the rate at which crystals nucleate. Photography will be used to study their evolution, with the hope of seeing white light backlit samples diffract the light so that the color changes with viewing angle. This will help reveal the shape of the nuclei, which provide information about the way the crystals grow in microgravity. The crystallites might grow fast in certain crystallographic directions which could give them a layer like structure. Also their shape will give some hints about the processes that limit the growth. Comparison with analogous ground-based experiments will reveal differences in the growth behavior in microgravity.
Studying crystals in microgravity conditions removes the influence of gravity and allows a clearer picture of the forces that cause crystals to grow. This helps scientists determine how particle size impacts the strength, temperature sensitivity and growth of crystal materials.
The BCAT-4-Poly experiment investigates two sets of microscopic spheres having a variety of sizes. Scientists determine how the size of the particles affects their ability to form crystalline structures by studying the high-resolution photographs taken in space by crewmembers during the crystal forming process. Results from the experiment help researchers develop specialized crystals for high-speed computers, optical devices and other advanced materials.
The BCAT-4 hardware consists of ten samples of colloidal particles. The microscopic colloid particles and a polymer (samples 8 - 10) are all mixed together in a liquid. The BCAT-4 samples are contained within a small case the size of a school textbook. The experiment requires a crew member to set up on the Maintenance Work Area (MWA) or on a handrail/seat track configuration, EarthKAM hardware and software to take digital photographs of samples 8 - 10 at close range using the onboard Kodak 760 camera. The pictures are then downlinked to investigators on the ground for analysis.Operational Protocols
A crewmember sets up all hardware on the Maintenance Work Area (MWA). The crewmember then homogenizes (mixes) the sample(s) and takes the first photographs, manually. The crewmember activates the EarthKAM software to automate the rest of the photography sessions over a 3-day to 3-week period. Crewmembers perform a daily status check to assure proper alignment and focus of the camera. At the completion of the session, a crewmember tears down and stows all hardware.
Ground Based Results Publications
Man WN, Donev A, Stillinger FH, Sullivan MT, Russel WB, Heeger D, Inati S, Torquato S, Chaikin PM. Experiments on random packings of ellipsoids. Physical Review Letters. 2005; 94: 198001.
Donev A, Cisse I, Sachs D, Variano EA, Stillinger FH, Connelly R, Torquato S, Chaikin PM. Improving the density of jammed disordered packings using ellipsoids. Science. 2004; 303(5660): 990-993. DOI: 10.1126/science.1093010.
Donev A, Stillinger FH, Chaikin PM, Torquato S. Unusually dense crystal packings of ellipsoids. Physical Review Letters. 2004; 92: 255506-1.
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.
BCAT-4 Slow Growth Sample Module.
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Cathy Frey (BCAT Crew Trainer) and Peter Lu (BCAT Investigator) showing astronaut Daniel Tani, time-lapse video of sample evolution from photos taken by Bill McArthur during ISS Expedition. 12.
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