Kitchen Cupboard Science

Here\'s a challenge for you: Using only what you can find laying around
your house, put together an experiment to test a question in science
that\'s never been answered.

That\'s essentially the challenge faced by some scientists doing
research on the International Space Station. While the shuttle fleet is
grounded, space for sending equipment up to the station is very limited.
So some researchers have found clever ways to do their experiments using
what\'s on hand aboard the station: maintenance tools, food supplies,
hygiene items, cameras, miscellaneous supplies \... and, of course,
weightlessness!

The surprisingly elegant experiments they\'ve devised are a showcase of
resourcefulness. Over the next few weeks, *Science@NASA* will feature a
series of articles about these experiments, showing how \"household\"
items can be used to do cutting-edge science.

One of these experiments was concocted by University of Southern
Mississippi chemistry professor John Pojman and collaborators..... They
want\\ to find out what happens when two miscible fluids are combined in
microgravity.

"Miscible means mixable," explains Pojman. "When miscible fluids are
combined, they merge. One diffuses completely into the other\--like
water and molasses. Immiscible fluids are just the opposite. They remain
separated\--like oil and water."

Sounds simple. But 100 years ago a Dutch physicist named [Diederik
Korteweg](http://staff.science.uva.nl/~janwieg/korteweg/) pointed out a
complication: sometimes miscible fluids act like immiscible fluids.

Indeed, you can see this in your own kitchen using water and molasses.
Fill a clear cup with water. Next, dip a spoon into a jar of molasses,
and tip the spoon into the water. A stream of pure goopy syrup will
plunge to the bottom of the cup. These two fluids are miscible, yet they
don't look like they're mixing. They appear to be immiscible. Eventually
the molasses will dissolve\--but it takes some time.

Like Pojman and his collaborators Nick and Willie of France, Korteweg
was fascinated by what happens during that time just after miscible
fluids are combined ... and just before they merge. Would they act like
immiscible fluids? In one respect they should, Korteweg argued.
Immiscible fluids tend to break apart into little droplets---a
side-effect of surface tension. Miscible fluids should break apart in
the same way, he calculated, during the earliest moments of gentle
mixing.

Drs. Vitaly Volpert and Nick Bessonov at the Université Lyon I in France
have performed simulations that show a stream of a miscible fluids can
break apart from the Korteweg stress and an elliptical drop will become
spherical -- just as seen with immiscble fluids. "The great unknown,"
says Pojman, "are the values of the parameter describing the
intermolecular interactions." Performing the experiment will help his
team estimate this value and to test their model.

This is important. Miscible fluids, gently mixed, are widely-used in the
plastics industry and they're important for certain types of medical
research---"especially protein crystal growth in microgravity," notes
Pojman.

Still, no one knows if Korteweg was right. "It's impossible to test his
theory on Earth because gravity overwhelms surface tension," experiments
Pojman. Fluid streams fall apart because of their own weight. "We need
to do this experiment on the space station."

The first thing they need for the experiment, which is called Miscible
Fluids in Microgravity (MFMG), is some kind of container in which to do
it. The container needn\'t be large, but it must be transparent so that
cameras can record the outcome.

Unused urine collection syringes fit the bill perfectly. Cameras that
the space station crew uses to document life in orbit fill the
data-acquisition roll. A video camera will film the entire 10-minute
experiment, and a digital still camera will snap shots every 30
seconds.\
\
While the body of one syringe serves as a container for the first fluid,
the needle of another syringe will slowly inject a stream of the second
fluid.

Air bubbles could spoil the experiment, Pojman says. To plug small holes
in the syringes that could introduce air bubbles, Pojman considered a
widely used sealant: chewing gum.\
\
\"I like the idea of an experiment that uses chewing gum,\" Pojman
jokes. Nevertheless, they ultimately chose to use Duxseal™, a plumber\'s
leak-repair compound from the station\'s maintenance kit.

Water was an obvious choice for the first fluid, but what about the
second one? Pojman says they considered several of the materials
available on the station: shampoo, shaving cream, even ultrasound gel.
(The space station is equipped with an ultrasound imager for use in
medical experiments.)\
\
In the end they settled on honey. The crew has cans of Russian honey on
board to use for sweetening their tea. As anyone who has had honey in
their tea before knows, honey dissolves in water quite nicely \--
*i.e.*, water and honey are miscible.\
\
One small Ziplock™ bag will serve as a reservoir for the water, and two
larger bags will dispose of the leftover waste.

Voilà! A world-class microgravity experiment, no custom-built equipment
required.

The experiment will probably take place before the end of this
year---and Pojman can't wait. \"Knowing whether Korteweg\'s theory is
true, and understanding the molecular interactions that underlie it,
would be a step forward for material science and fluids physics," he
says.

It's amazing what you can accomplish using odds and ends around the
house ... and a little ingenuity.