Engineering researchers have discovered that under the right circumstances, basic atomic forces can be exploited to enable nanoparticles to assemble into superclusters that are uniform in size and share attributes with viruses. Image: T.D.Nguyen, Glotzer Group, University of Michigan |
A delicate balance of atomic forces can be exploited to make
nanoparticle superclusters that are uniform in size—an attribute that’s
important for many nanotech applications but hard to accomplish, University of Michigan researchers say.
The same type of forces are at work bringing the building
blocks of viruses together, and the inorganic supercluster structures in this
research are in many ways similar to viruses.
U-M chemical engineering professors Nicholas Kotov and Sharon
Glotzer led the research. The findings are published online in Nature Nanotechnology.
In another instance of forces behaving in unexpected ways at
the nanoscale, they discovered that if you start with small nanoscale building
blocks that are varied enough in size, the electrostatic repulsion force and
van der Waals attraction force will balance each other and limit the growth of
the clusters. This equilibrium enables the formation of clusters that are
uniform in size.
“The breakthrough here is that we’ve discovered a
generic mechanism that causes these nanoparticles to assemble into near perfect
structures,” Glotzer says. “The physics that we see is not special to
this system, and could be exploited with other materials. Now that we know how
it works, we can design new building blocks that will assemble the same
way.”
The inorganic superclusters—technically called
“supraparticles”—that the researchers created out of red, powdery
cadmium selenide are not artificial viruses. But they do share many attributes
with the simplest forms of life, including size, shape, core-shell structure,
and the abilities to both assemble and dissemble, Kotov says.
“Having these functionalities in totally inorganic
system is quite remarkable,” Kotov says. “There is the potential to
combine them with the beneficial properties of inorganic materials such as
environmental resilience, light adsorption and electrical conductivity.”
Zhiyong Tang, a collaborating professor at the National
Center of Nanoscience and Technology in China, says, “It is also very
impressive that such supraparticles can be further used as the building blocks
to fabricate three-dimensional ordered assemblies. This secondary self-assembly
behavior provides a feasible way to obtain large-scale nanostructures that are
important for practical application.”
Kotov is currently working on “breeding” these supraparticles
to produce synthetic fuels from carbon dioxide. The work also has applications
in drug delivery and solar cell research and it could dramatically reduce the
cost of manufacturing large quantities of supraparticles.
“By replicating the self-assembly processes that allow
living organisms to grow and heal, we can simplify the production of many
useful nanostructured systems from semiconductors and metals so much so that
they can be made in any high school laboratory,” Kotov says.
