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Microgravity Phase Separation Near the Critical Point in Attractive Colloids

We investigate the phase behavior of mixtures of colloids and polymers near their critical point in a microgravity environment. Astronauts onboard the International Space Station (ISS) are using photography to record the rate of phase separation of six samples near the liquid-gas critical point. These photographs are taken both by an automated photograpy system (based on EarthKAM hardware and software) and manually by the astronuats who have setup the experiment. We have obtained high-quality photographs of processes that are not observable on Earth, since both sedimentation and convection are negligible onboard the International Space Station. Interestingly, we observe that gravity does not affect the onset of phase separation in colloid-polymer mixtures near the liquid-gas critical point: samples which phase separate on earth also do so onboard the ISS. However, the rates at which this phase separation occurs is affected by several orders of magnitude by gravity, suggesting future avenues for exploration. The understanding of this system is important for both practical earth-bound applications, as well as the development of products and materials that are stable and function over long periods of time in a low-gravity environment. Thus, our results may assist the long-term spaceflight required for proposed exploration missions to the moon and to Mars.

Related URLs:
http://dx.doi.org/10.2514/6.2007-1152