Tiny plastic fibers could be the key to some diverse technologies in
the future -- including self-cleaning surfaces, transparent
electronics, and biomedical tools that manipulate strands of DNA.
In the June issue of the journal Nature Nanotechnology, Ohio State
University researchers describe how they created surfaces that, seen
with the eye, look as flat and transparent as a sheet of glass. But
seen up close, the surfaces are actually carpeted with tiny fibers.
The patent-pending technology involves a method for growing a bed of
fibers of a specific length, and using chemical treatments to tailor
the fibers' properties, explained Arthur J. Epstein, Distinguished
University Professor of chemistry and physics and director of the
university's Institute for Magnetic and Electronic Polymers.
"One of the good things about working with these polymers is that
you're able to structure them in many different ways," Epstein said.
"Plus, we found that we can coat almost any surface with these fibers."
For this study, the scientists grew fibers of different heights and
diameters, and were able to modify the fibers' molecular structures by
exposing them to different chemicals.
They devised one treatment that made the fibers attract water, and
another that made the fibers repel water. They found they could also
make the surfaces attract or repel oil. Depending on what polymer they
start with, the fibers can also be made to conduct electricity.
The ability to tailor the properties of the fibers opens the surface to many different applications, he said.
Since dirt, water, and oil don't stick to the repellant fibers, windows coated with them would stay cleaner longer.
In contrast, the attracting fibers would make a good anti-fog
coating, because they pull at water droplets and cause them to spread
out flat on the surface.
What's more, researchers found that the attracting surface does the
same thing to coiled-up strands of DNA. When they put droplets of water
containing DNA on the fibers, the strands uncoiled and hung suspended
from the fibers like clotheslines.
Epstein said scientists could use the fibers as a platform to study
how DNA interacts with other molecules. They could also use the
spread-out DNA to build new nanostructures.
"We're very excited about where this kind of development can take us," he added.
Epstein's research centers on polymers that conduct electricity, and
light up or change color. Depending on the choice of polymer, the
nano-fiber surface can also conduct electricity. The researchers were
able to use the surface to charge an organic light-emitting device -- a
find that could pave the way for transparent plastic electronics.
Finally, they also showed that the fibers could be used to control
the flow of water in microfluidic devices --- a specialty of study
co-author L. James Lee, professor of chemical and biomolecular
engineering and head of Ohio State's Center for Affordable
Nanoengineering of Polymeric Biomedical Devices.
Lee and Epstein are advisors to former graduate student Nan-Rong
Chiou, who developed the technology to earn his doctorate. He is now a
visiting scholar at the university. Other co-authors on the paper
included former doctoral students Chunmeng Lu and Jingjiao Guan.
The technology is a merger of two different chemical processes for
growing polymer molecules: one grows tiny dots of polymer "seeds" on a
flat surface, and the other grows vertical fibers out from the top of
the seeds. The fibers grow until the scientists cut off the chemical
reaction, forming a carpet of uniform height.
The university will license the technology, and Epstein and his colleagues are looking for new applications for it.
Aside from anti-fog windows, self-cleaning windows, and organic
LEDs, Chiou said that he foresees the surfaces working in glucose
sensors, gene therapy devices, artificial muscles, field emission
displays, and electromagnetic interference shielding.
This research was partially funded by the National Science Foundation.
Source: http://researchnews.osu.edu
