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Chemists and physicists have succeeded in getting custom-shaped microparticles
to interact and self-assemble in a controlled way in a liquid crystal.
 | | Polarized light microscopy image of a square microparticle in liquid crystal |
The research, federally funded by the National Science Foundation, appears
in the Nov. 20 edition of the journal Science.
"We're learning the rules about how these lithographic particles self-assemble,"
said Thomas G. Mason, a UCLA
professor of chemistry and physics and a member of the California NanoSystems
Institute at UCLA. "This method may enable us to cause them to assemble
in desired configurations."
The scientists anticipate that their "LithoParticles," which are made
of solid polymeric materials, will have significant technological and scientific
uses.
"We're examining how pairs of particles interact and come to attach together,"
Mason said. "If we can get the particles to interact in certain controlled
ways, we can build larger-scale assemblies that may have applications in photonics,
optical communication networks and a variety of other areas."
Mason and his colleagues — lead author Clayton Lapointe, a postdoctoral
scholar at UCLA, formerly at the University of Colorado at Boulder, and Ivan
Smalyukh, an assistant professor of physics at the University of Colorado at
Boulder — used an optical microscope to study the attractions between
the particles, which they custom designed in various shapes, including triangles,
squares and pentagons. The particles are too small to see with the unaided eye
but are quite clear with the instrument.
"This is a very complex material that we have created," said Mason,
whose research is at the intersection of chemistry, physics, engineering and
biology. "We have made lithographic particles dispersed in a liquid crystal,
and the molecular constituents are aligned."
Particles of different shapes interact in different ways, Lapointe, Mason and
Smalyukh report. Those with an odd number of sides, such as triangles and pentagons,
interact differently than particles shaped like squares.
"In this environment, the particles have different kinds of interactions
that depend on their shapes," Mason said. "We have shown in a systematic
way how by changing the number of sides of the particles in a controlled way,
we can characterize the differences in their interactions."
The scientists added materials to the liquid crystal to get the particles to
attract. They produced the geometric particles using the same method Mason and
his UCLA used to design and mass-produce billions of fluorescent microscale
particles in the shapes of all 26 letters of the alphabet, as well as geometric
shapes, such as triangles, crosses and doughnuts, in 2007. Now they have watched
the particles interact.
In another paper, UCLA postdoctoral scholar Kun Zhao and Mason report discovering
new states of matter in two dimensions. Their research, which appears in the
Nov. 13 edition of the journal Physical Review Letters, focused on a two-dimensional
surface with pentagon-shaped particles that were free to move on this surface.
Zhao and Mason studied the structures as they increased the area fraction of
the pentagons in the confined two-dimensional plane. They used a lithographic
technique to make the particles and studied them in water on a flat glass surface.
Posted November 24th, 2009
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