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| <p>BCAT-3 weekly report (12 April 2004) for collected highlights.</p> | |
| <p><strong>Astronaut Mike Foale wins critical acclaim from NASA investigators for his photographs that capture dynamic critical phenomena.</strong></p> | |
| <p>The Principal Investigators for the BCAT-3 experiment that is presently operating on the International Space Station (ISS) have compiled the photographs that astronaut Mike Foale has taken during the first 11 days of this bench-top microgravity experiment. The quality of these photographs is being described as outstanding. Figure 1 shows the dynamic process of phase separation for the first six BCAT-3 samples from Harvard (David Weitz and Peter Lu). Because these samples are very close to the critical point (a unique point where a liquid and gas are no longer distinguishable), those samples which do phase separate, separate very slowly. This is because near the critical point the surface tension is MUCH lower (since the correlation lengths are larger). This process is important in many areas, some of which are mentioned at HYPERLINK "http://exploration.grc.nasa.gov/life/bcat3_iss.html" http://exploration.grc.nasa.gov/life/bcat3_iss.html. Using colloids to study criticall phenomena is nice because colloids are much bigger than atoms; for these samples the times scales are slowed down (Figure 2) and length scales are easily visualized (please see Figure 1). </p> | |
| <p>It's still too early to make any definitive comments on the U. Penn surface crystallization samples (samples 8, 9, and 10). Professor Yodh and Jian Zhang at U. Penn. have noticed what may be phase separation in sample 10; and they are seeing hints of what may be the presence of surface crystals in sample 9.</p> | |
| <p>Figure 1 shows the time evolution of those samples in the BCAT-3 experiment that are undergoing phase separation. Sample 1 is completely phase separated and samples 4 and 5 have not phase separated, as expected. This allows the critical point to be determined to within a 1/10 of a percent.</p> | |
| <p>Figure 2 shows the time evolution of the characteristic size of the colloid-rich regions of the BCAT-3 samples (1-6) as a function of time.</p> | |
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