One idea at the forefront of nanoassembly is to use the properties of certain
nano and microparticles to have them assemble themselves into something useful.
Researchers at the Weizmann Institute recently discovered that when left to
fend for themselves, long carbon nanotubes will fall in such a way as to create
a semi-ordered structure. As the nanotubes themselves possess many
properties favorable to these applications, this sort of simple nanoassembly
could be used to quickly and easy create microscale radiators or antennas for
tiny electronic devices.
This week, University of Pennsylvania researchers published results in the
journal Nano Letters that outline the use of a common silicon polymer,
known as polydimethylsiloxane or PDMS, to create
nanoscale patterns of suspended solids. Their PDMS molds are highly
durable, reusable many times over. Due to the material's flexibility and
durability, it can also be used to transfer the patterns to various non-flat
surfaces. To add even more value, the nanoscale patterning process is also much
cheaper than standard chemical lithography.
PDMS is so common, you've probably never heard of it. But its properties are
what make it an ideal substance for Penn's use. At low temperatures, the polymer
acts like an elastic solid, rubber for example. If a cube of PDMS were dropped
on a table, it would bounce. At the same time, it can be pulled and formed into
different shapes. At higher temperatures, the material flows faster, like
molasses or honey. It will flow into surface irregularities on a surface if
left alone, which makes it useful for various industrial applications deal with
If these properties sound familiar, it's because you've probably enjoyed
something like it as a child: Silly Putty. Silly Putty is, in fact, about 4%
PDMS. It can also be found in everything from cosmetics to medical devices to
contact lenses to caulking to lubricant. It's even used in food additives and
in treatments for head lice.
To form their nanoscale patterns, Penn researchers created a layer of PDMS gel
on a grid of silicon pillars, 1 µm in diameter, each spaced 2 µm apart. In
order to create the “diamond plate” pattern they used, the group harnessed
known properties of these gels to swell while wetted by a solvent. The circular
pores created in the material eventually deform elliptically along the same
axis due to elastic interaction while the polymer is swelled under the
influence of the solvent.
To create the pattern itself, the Penn group dissolved Fe3O4 nanoparticles into
toluene solvent to create a solution. The PDMS gel is then bathed in the
solution. The swelling mechanism creates the desired pore patterns, and the
nanoparticles flow into place due to convection. Once the pattern is
transferred, and the polymer removed from the solution, it returns faithfully
to its original form.
“These functional nano-motifs could in turn benefit novel technologies that are
sensitive to local environment change such as smart clothing, biomarkers and
eco-friendly buildings. Using similar pattern transformation principles, our
technique could be extended to pattern a variety of material systems such as
polymers and composites, creating a new design mechanism for nanoscale
manufacturing,” explained assistant professor Shu Yang of Penn's School of
Engineering and Applied Science, Department of Materials Science and
Nanopatterning could certainly benefit several fields currently being explored
by nanotech researchers. Tiny electrical circuits require tiny conductors in
fine patterns; plasmonics and photonics both utilize microscopic patterns to
coerce particle/waves into specific modes or places, just to name a few.
Anything that could benefit from smaller mechanical and electrical devices,
especially in the medical field, could see an impact from technology such as
Penn's cheap, reusable nanoscale patterning mechanism.