Diffraction pattern from the AB6 binary colloidal crystal alloy; 11 days, 4 hr after melting; q, effective scattering angle.
Long description of figure 1.
Phase separation of the colloid-polymer critical point sample.
Long description of figure 2.
Gelation and aging of colloid-polymer gel sample.
Long description of figure 3.
Aggregation behavior of polystyrene fractal gel sample. Left: Polystyrene gel-high-magnification image taken 10 days after constituent combination, showing aggregation occurring. Right: Polystyrene gel-static light scattering performed both before and after constituent combination; a tremendous increase in scattered light occurs.
Long description of figure 4.
The Physics of Colloids in Space (PCS) experiment was accommodated within the International Space Station (ISS) Expedite the Processing of Experiments to Space Station (EXPRESS) Rack 2 and was remotely operated from early June 2001 until February 2002 from NASA Glenn Research Center's Telescience Support Center in Cleveland, Ohio, and from a remote site at Harvard University in Cambridge, Massachusetts. Remote operations enabled a significant number of hours of run time for this experiment with just a small number of ISS crew hours expended. PCS is an experiment conceived by principal investigator Professor David A. Weitz of Harvard University and coinvestigator Peter N. Pusey of the University of Edinburgh. It focused on the behavior of three different classes of colloidal suspensions (binary colloidal crystal alloys, colloid-polymer mixtures, and fractal gels). A colloidal suspension consists of fine particles (micrometer to submicrometer) suspended in a fluid, examples being paint, milk, salad dressings, and aerosols. The potential payoffs of PCS are improvements in the properties of paints, coatings, ceramics, and food- and drug-delivery products; improved manufacturing of products requiring either colloidal suspensions for processing or as precursors; and important first steps in the research and development of an entirely new class of materials that passively affect the properties of light passing through them. The sophisticated light-scattering instrumentation comprising PCS is capable of color imaging, dynamic and static light scattering from 11° to 169°, Bragg scattering from 10° to 60°, and laser light scattering at low angles from 0.3° to 6.0°. The PCS instrumentation performed remarkably well on orbit, demonstrating a flexibility that enabled experiments to be performed that had not been envisioned prior to launch.
While on-orbit on the ISS, PCS completed 2400 hours of science operations, and the principal investigator declared it to be a resounding success. Each of the eight sample cells worked well and produced interesting and important results. Crystal nucleation and growth and the resulting structures of two binary colloidal crystal alloys were studied, with the long-duration microgravity environment of the ISS facilitating extended studies on the growth and coarsening characteristics of the crystals. In another experiment run, the demixing of the colloid-polymer critical point sample was studied as it phase-separated into two phases, one that resembled a gas and one that resembled a liquid. This process was studied over four decades of length scale (from 1 mm to 1 cm) to observe behavior that could not be seen in this sample on Earth because sedimentation would cause the colloids to fall to the bottom of the cell faster than the demixing process could occur. To acquire this data, the PCS science and operations teams codesigned and coexecuted a unique diagnostic sequence that captured and condensed the first 16 hr of this sample’s demixing into a 7-s time-lapse movie. In addition, the study of the gelation and aging of another colloid-polymer sample, the colloid-polymer gel, provided valuable information on gelation mechanisms, as did investigations on the extremely low concentration silica and polystyrene fractal gel samples. In virtually all cases, we enhanced our understanding of the science being investigated.
The PCS experiment was developed, launched, and operated by Zin Technologies under NASA contract NAS3- 99154. PCS was deorbited in June 2002. The hardware will be replenished with another set of eight colloidal samples and is planned for relaunch in 2003.
Find out more about this research:
Glenn’s PCS research (includes data on a sample-by-sample basis--being updated)
Principal investigator’s group at Harvard (scientific focus areas of interest; external site)
Glenn’s microgravity research
Glenn’s fluid physics research
Glenn contact: Michael P. Doherty, 216-433-6641, Michael.P.Doherty@nasa.gov
National Center for Microgravity Research contact: Dr. Subramanian Sankaran, 216-433-9335, Subramanian.Sankaran@grc.nasa.gov
Authors: Michael P. Doherty and Dr. Subramanian Sankaran
Headquarters program office: OBPR
Programs/Projects: Microgravity Science
Last updated: June 25, 2003
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216-433-8258
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