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July 23, 1996
CONTACT: Phil Sneiderman
In Earthbound Labs, Researchers Unravel the
You don't need to rocket into space to find out how chemicals
will behave when gravity is gone, two researchers at the Johns
Hopkins University say. Both are engaged in microgravity research
funded by NASA, yet their
experiments are taking place almost entirely within campus labs.
Paulaitis, chair of the Department of Chemical
Engineering, has found a way to mimic the way chemicals mix in
weightless conditions. His work could shape the way new polymers
are made aboard a future space station.
Low-Gravity Physics Of Outer Space
Kathleen Stebe, an associate
professor in the same department, is
studying the movement of immiscible fluids--ones that don't
dissolve into one another, such as oil and water. Her findings
could influence the way fuel is pumped aboard a spaceship--as
well as the way ink-jet cartridges and pharmaceuticals are
manufactured on Earth.
Yet neither is scrambling to put experiments aboard the space
shuttle. To place research work on these vessels, scientists face
stiff competition and a long wait. And because shuttle flights
are short, and many scientific experiments are scheduled for each
flight, astronauts have little time to devote to any one
experiment. As a result, studying the effects of low gravity
without going into space saves money and often yields more
results, says Paulaitis, who recently joined JHU's Whiting School
of Engineering faculty.
"When you do experiments in the space shuttle, you don't have
much latitude for doing what scientists and engineers do best,"
he says. "They make predictions, they try out their predictions,
they make mistakes, and they learn from them. Then they go on and
do it better the next time.
"It takes several years to get an experiment onto the space
shuttle, and during that time your experiment is carefully
planned and meticulously designed. Because of that, you don't
play a lot of 'what ifs' once your experiment is in space. You
don't have the luxury to try a lot of different experiments to
come up with the best science. It's more cost-effective, and
it's probably the most efficient use of time to try many
experiments like these on Earth first."
Paulaitis' research focuses on polymers, and outer space promises
to be a fertile new environment for creating them. Polymers are
very large molecules consisting of long, interconnected chains of
smaller molecules. These macromolecules are the basis for many
important materials, including plastics, synthetic fibers and
coatings. They form when the smaller molecules, called
monomers, come in contact and react or "polymerize" to form
chains. These chains then react with more monomers to form longer
chains, and eventually the polymer.
Invariably, the large polymer molecules will not mix with the
much smaller monomer molecules, and the polymer separates or
precipitates to form another distinct liquid or solid phase. This
precipitation or phase separation slows down or completely stops
the polymerization process.
But scientists often want the polymerization process to continue,
so that a particular polymeric material is produced. To encourage
this process, scientists and engineers can prepare a stable
suspension in which the polymer phase does not separate from the
phase containing the monomer.
Yet making such suspensions can be a problem on Earth, where
gravity causes the two phases to separate quickly. Think of a can
of soda pop when it is opened and the pressure inside is
released. The lighter gas bubbles "fizz," or phase-separate, from
the heavier liquid soda pop and rise to the top. In the
weightlessness of space, this separation would occur very slowly.
Meanwhile, the bubbles would remain suspended throughout the
container. If the gas bubbles contained monomer molecules, and
the liquid soda pop contained the polymer that is being formed
from them, this weightless suspension would be a good medium for
making polymers because it would keep the two key ingredients
close to one another.
Paulaitis has found a way to recreate this effect on Earth. By
combining water, carbon dioxide and a surfactant (for example,
soap) under pressure, he has developed a unique solution that
forms two phases with the same density. Because of this, these
phases do not readily separate. Instead, they form a stable
suspension--a friendly environment for forming polymers.
Over the next four years, Paulaitis plans to study how this
suspension forms, how long it remains stable, and how its
properties change with time. This is important because the
properties of a polymer material--whether it is flexible or
stiff, hard or soft, for example--are related to the
environment in which it forms. Paulaitis' collaborator, Professor
Eric Kaler at the University of Delaware, will try to create new
polymers in this mixture.
To confirm their results, the professors plan to ask NASA to
recreate some of their experiments aboard a shuttle flight in
three or four years. But ultimately, Paulaitis believes their
findings on Earth may form a blueprintfor creating a wide variety
of new polymers in space.
In her own lab at Hopkins, Stebe is using a NASA grant to study
the motion of immiscible fluids; for instance, the movement of
drops and bubbles suspended in other fluids. Specifically, her
research focuses on the dynamics of fluid interfaces and how they
are affected by surfactant molecules. A simple example of an
interface is the surface of a water drop--the boundary between
water and air. When a droplet moves in air, its interface also
Surfactants are molecules that possess one segment that prefers
to be in water and another that does not. To keep both pieces
"happy," or minimize their energy, the molecules sit at
interfaces, so that one part can remain in water and another can
stick out. This reduces the surface tension. If the density of
surfactant at the interface increases, the surface tension
decreases still further. As a result, the motion of the interface
depends on the amount of surfactant on it.
Surface tension causes interfaces to resist stretching. That's
why droplets and bubbles try to remain spherical--to minimize
their surface area. Reducing the surface tension by adding
surfactants can improve the ability of droplets to deform and mix
with other fluids.
Understanding this process can improve our ability to control
immiscible fluid systems. That can produce benefits in space and
on Earth. "NASA's interest is because they're constantly moving
fluids from one place to another in space," says Stebe. "They are
interested in the fundamental issues behind fluid flow in order
to use it effectively in microgravity."
On Earth, Stebe's research could lead to advances in the booming
surfactant industry, where global sales in 1996 are expected to
approach $10 billion, according to one recent estimate.
Surfactants play a key role in a wide array of applications that
require the mixing of two immiscible fluids. These include the
creation of coatings for textiles and paper, formulation of inks
and paints, and development of biomedical diagnostic tests.
Manufacturers have used surfactants for many years, but they know
very little about how their molecular structure influences their
properties at interfaces, Stebe says. "It's sort of like
wine-making in ages past," she says. "The practice ran way ahead
of our fundamental understanding of the science behind it."
These microgravity research projects are being funded entirely by
NASA. Paulaitis and Kaler will receive almost $500,000 over four
years. Stebe will receive approximately $310,000, also over four
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