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Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5-SeededGrowth)
12.26.08

Overview | Description | Applications | Operations | Results | Publications | Images

Experiment/Payload Overview

Brief Summary

he Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5- SeededGrowth) experiment will study the properties of concentrated systems of small particles in an index matching fluid when the particles are all monodisperse "hard spheres", except for about 0.2 percent of them that are approximately 11.5 times larger in diameter. The larger "seed" particles, which may induce crystallization by heterogeneous nucleation. The theoretical prediction is that the use of the right size and concentration of seed particles (nano-dirt) can be used as a way to control the size of crystallites by reducing the free-energy barrier associated with crystal nucleation.

Principal Investigator

  • Paul Chaikin, Ph.D., New York University, New York, NY

    • Co-Investigator(s)/Collaborator(s)

  • Andrew Hollingsworth, Ph.D., New York University, New York, NY

    • Payload Developer

    Glenn Research Center, Cleveland, OH
    ZIN Technologies, Cleveland, OH

    Sponsoring Agency

    National Aeronautics and Space Administration (NASA)

    Expeditions Assigned

    |19|20|21|22|

    Previous ISS Missions

    The predecessors to BCAT-5, which are BCAT-3 and BCAT-4 are in operation on the ISS.

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    Experiment/Payload Description

    Research Summary

    • Binary Colloidal Alloy Test - 5: SeededGrowth (BCAT-5-SeededGrowth) is one of four investigations in the BCAT-5 suite of experiments. BCAT-5-SeededGrowth utilizes sample 9 in the BCAT-5 hardware.


    • Colloids like these are a nice model for atoms, and they have the advantages that they are big enough to interact with visible light, which lets us see what's going on, and big enough to slow things down, allowing us to watch the formation of structures. On Earth, gravity causes the colloids to settle, making such a study particularly difficult. Performing these experiments in the microgravity environment of the ISS will allow scientists to study the growth of larger structures, enabling them to observe the behaviors of large model atoms.


    • 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 that are glass-like on earth crystallize in microgravity.


    • The effects of polydispersity and spherical seed particles on the crystal nucleation barrier and the structure of the critical nucleus have been examined by Frenkel, et al. The recent numerical simulations make predictions concerning the structure and free energy of colloidal crystal nuclei, which will be tested. Classical nucleation theory does not capture the general experimental observation that the rate of crystal nucleation passes through a maximum as the supersaturation is increased. The experimental results obtained in microgravity should be very helpful in directing future modeling and will provide the experimental input that is critical for forming and testing new models.


    • BCAT-5-SeededGrowth scientists expect that work with hard spheres model systems that contains seed particles will address questions about crystallization may be studied aboard the International Space Station (ISS) without the perturbing effects of sedimentation and gravitational jamming.

    Description

    he 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.

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    Applications

    Space Applications

    BCAT-5-SeededGrowth will ultimately impact our understanding of the strength and thermal conductivity of materials by providing insight into the effects of polydisperity and the presence of larger ?seed? particles in dense suspensions of particles.

    Earth Applications

    Generally, colloidal nucleation experiments seek an understanding of the most fundamental liquid/solid transition. The relative uniformity in size of particles may impact the rise of order out of disorder. Though direct applications of that understanding do not yet drive the research, growth of ordered colloidal phases has attracted interest in a number of areas, e.g. ceramics, composites, optical filters and photonic bandgap materials.

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    Operations

    Operational Requirements

    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.

    Operational Protocols

    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.

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    Results/More Information

    Information Pending

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    Related Web Sites

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    Publications

    Results Publications

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      Related Publications
      • Cacciuto A, Auer S, Frenkel D. Onset of heterogeneous crystal nucleation in colloidal suspensions. Nature. ;428, 404-406. 2004
      • 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. ;309, 1231-1233. 2005

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      Images

      imageNASA 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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      Information Provided and Updated by the ISS Program Scientist's Office
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