surface crystallization (BCAT-3-SC) investigation examines whether materials in fluids prefer to
first crystallize at a surface or in the fluid volume when gravity is removed. This impacts how
fluids should be stored. Supercritical fluids, which are one of the applications of the critical
point (BCAT-3-4-CP) experiment, are of potential application in propulsion systems for future
spacecraft design.
RESULTS
BCAT-3-BA (PUSEY)
Unfortunately, the BCAT-3-BA sample dried out before crystallizing could occur aboard ISS.
BCAT-3-SC (YODH)
During the surface
crystallization (BCAT-3-SC)
experiment, astronauts
photographed samples of
suspended colloidal
particles in a liquid that
contains a small amount of
polymer to document the
formation of colloidal
crystals. Under the right
circumstances these
suspended particles will
prefer to crystallize on the
container surfaces, rather
than in the sample volume.
Three BCAT-3-SC samples
will study the formation of
colloidal crystals confined
to a surface, allowing
comparison with bulk 3-D crystallization, to begin testing how geometry affects crystallization
itself. Results will help scientists develop fundamental physics concepts previously hindered by
the effects of gravity. Ordered arrays of these micron-sized particles might be ideal for
switching and controlling light. Imagery for the BCAT-3-SC was collected over several missions
and is still undergoing analysis.
BCAT-3-4-CP (WEITZ)
The BCAT-3-4-CP samples have yielded some surprising results; the samples that separated on
Earth also separated in space; the samples that did not separate on Earth also did not separate
in microgravity, indicating that the tendency for phase separation is not linked to gravity.
However, for those samples that separated into different phases, the rates of separation for the
microgravity samples were very different from the same mixtures on Earth.
Those samples with concentrations closest to the critical point took weeks to months in
microgravity, compared with a couple of days on Earth (Lu 2007).
ISS016E027863 – Astronaut Dan Tani photographing the Binary Colloidal
Alloy Test - 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.