Janus particles offer new
physics, new technology
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[APRIL 12, 2006]
CHAMPAIGN -- In Roman mythology, Janus was the
god of change and transition, often portrayed with two faces gazing
in opposite directions. At the University of Illinois at
Urbana-Champaign, Janus particles are providing insight into the
movement of molecules and serving as the basis for new materials and
the surface of colloidal particles into a Janus chemical compound,
we can measure the rotational dynamics of single colloidal particles
in suspension as well as at interfaces," said Steve Granick, a
professor of materials science
chemistry, and physics.
"We can also take advantage of the particles' two very dissimilar
sides to create families of microsensors."
metal-deposition technique, Granick and his research team --
graduate students Liang Hong and Steven Anthony and postdoctoral
research associate Huilin Tu -- make particles half-covered by metal
and generate geometrically symmetric but chemically asymmetric
materials. Trapped inside the micron-size particles are fluorescent
dyes, which can be seen only through the uncoated hemisphere, not
through the metal-coated hemisphere.
"Because these colloidal particles are rotating, they twinkle as
they move back and forth, 'swimming' by Brownian motion," said Granick, who is also a researcher at the
Frederick Seitz Materials
Research Laboratory and at the
Beckman Institute for
Advanced Science and Technology. "By carefully monitoring the
motion of the particles, we can now ask questions about that motion
that were not possible before."
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Individual particles can be tied together like strings of pearls.
Using precision imaging and tracking techniques, the researchers can
measure the movement as the strings tumble around. The particles can
also be used as microprobes and microrheometers.
"We are continuing to explore the chemical modification of the
metal surface to form new colloid-based materials," said Granick,
who presented his team's work at the March 13-17 meeting of the
American Physical Society at the Baltimore Convention Center. "We
are also investigating the use of electrical fields and magnetic
fields to manipulate the particles."
The U.S. Department of Energy funded the work.
[James E. Kloeppel, physical sciences editor,
of Illinois at Urbana-Champaign news bureau]