In Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3D-Melt), crewmembers photograph specially designed microscopic particles (colloids) suspended in a liquid over a period of time. The particles are designed to melt when temperatures warm above 23°C (when the station is warmed by sun) and crystallize when the temperatures drop below 23°C (when the Earth blocks the sun). The results help scientists develop fundamental physics concepts which are important in developing next generation technologies in computers and advanced optics.Principal Investigator(s)
ZIN Technologies Incorporated, Cleveland, OH, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)ISS Expedition Duration:
March 2009 - October 2013
19/20,21/22,25/26,27/28,29/30,31/32,33/34,35/36Previous ISS Missions
The predecessors to BCAT-5, BCAT-3 and BCAT-4 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-5-3D-Melt sample will consist of a monodisperse nearly-hard-sphere colloidal suspension near its crystallization point. For this investigation small temperature changes that change the particle volume fraction will move the equilibrium system towards and away from the melting transition. The key ingredient in these samples is a thermosensitive polymer, poly(N-isopropylacrylamide (NIPA); the temperature-sensitive character of the samples stems from the temperature dependent solubility of NIPA polymer in water. Below its theta temperature (the temperature at which the coiled polymer molecules expand to their full contour lengths and become rod-shaped) of approximately 31 degrees C, water is a good solvent and NIPA polymer assumes a swollen coil form; in this regime a small increase of temperature increases monomer-monomer attractions and thus the size of the isolated polymer decreases. Above the theta temperature, water is a poor solvent and NIPA has a collapsed globule form.
The BCAT-5-3D-Melt experiment will simply record sample temperature and observe (by photography) whether the sample crystallizes, noting at what temperature the sample experiences the fluid-solid transition. This information will be also be useful for future experiments planned for ISS.
BCAT-5 will ultimately impact our understanding of the strength and thermal conductivity of materials by providing insight into the effects of size variation in dense suspensions of particles. For example, the careful selection of crystallization promoters for controlling the crystallite size and size distribution may lead to improvement in materials fabrication processes. The suppression of crystal nucleation in polydisperse colloids has important implications for the morphology of polycrystalline materials.Earth Applications
BCAT-5 will evolve the field of colloidal engineering, which creates materials with novel properties using colloidal particles as precursors. To piece together answers to the scientific puzzles being studied, BCAT-5 takes advantage of the microgravity environment on the ISS to prevent the colloidal particles in these samples from encountering sedimentation, convection, and gravitational jamming.
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 the Maintenance Work Area (MWA) or on a handrail/seat track configuration. Initially the sample will require manual photographs to be downlinked by an astronaut to investigators on the ground for analysis. Following configuration confirmation from investigators the automated EarthKAM software will be setup to take digital photographs of samples 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 for how many days) once it is running. 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 of 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.