61
That’s the central idea of the enabling technology
behind the Center for Layered Polymeric Systems
(CLiPS), headquartered at Case Western Reserve
University. The center is using a co-extrusion process
that takes two polymer melts and combines them as
two layers, multiplies the layers to four, and doubles
that again as many times as desired.
“Pretty soon you have thousands of layers of
alternating polymers—as many as perhaps 4,000, and
these layers can be as thin as 50 angstroms,” says
center director Anne Hiltner, the Herbert Henry Dow
Professor of Science and Engineering in the department
of macromolecular science and engineering at Case.
Serving as research chair of the center at Case is
Eric Baer, who holds the Leonard Case Professor of
Engineering.
When polymers are combined in this so-called
“forced assembly,” magical things can happen. The
multilayered material can behave quite differently
than the starting ingredients. What was once brittle
becomes ductile in a multilayer. Colorless ingredients
now give off a color without the presence of dyes.
CENTER FOR LAYERED POLYMERIC SYSTEMS C L i P S
SPLIT IT,
SPREAD IT, AND
RECOMBINE IT:
STRATEGY FOR MAKING MULTILAYERED
MATERIALS WITH NOVEL PROPERTIES
Anyone who has made croissant dough
or puff pastry knows the process: roll the
dough very thin, spread it with butter,
fold it over, roll it again and repeat many
times to produce a fl aky pastry.
provide such a barrier were described by center
researcher David Schiraldi at a meeting of the
American Chemical Society in March 2007. Schiraldi
is associate professor of macromolecular science and
engineering at Case. His goal is to develop a glass
with excellent barrier properties and that melts at a
low enough temperature to be fl uid at the processing
temperature of the polymer.
Another thrust deals with barriers and membrane
systems that have applications, for example, in the
food industry. Keeping vegetables fresh requires that
the packaging material allow the right exchange
of gases in and out of the package. Because each
vegetable has unique needs in terms of gas transport,
researchers are exploring the possibility of tailoring
the performance of multilayered materials to extend
shelf life of produce and perhaps even control the
timing of ripening of packaged fruit.
The co-extrusion process offers the advantages
of simplicity, compatibility with existing polymer
materials, and scale of production. “We can take a
polymer off the shelf and do it—and we can make
miles of the stuff,” says Hiltner. “None of this ‘little
milligram quantities’ and laborious synthesis and
worrying about scale-up,” she notes. “We have two
co-extrusion lines and it’s not a particularly diffi cult
process once you have it set up and know how to work
it—so it’s really good for students. The students run
it and we have undergraduates who can help and even
have had high school students help. So it’s a process
that can be very hands on for the students.”
As layers become thinner and thinner, the effect
of the interface between these materials begins
to dominate, says center investigator Donald Paul,
professor of chemical engineering at the University of
Texas at Austin and director of the Texas Materials
Institute. “What happens is not so well understood,” he
admits. “Therein lies the frontier.”
CLiPS researchers are working at the intersection
of polymer science, engineering, chemistry, physics,
and biology to catalyze research and application of
this nanoscale technology and facilitate its translation
to the commercial sector through partnerships with
industry and other organizations.
In addition to fundamental research on the polymer
science and engineering, one research thrust at
CLiPS focuses on optical and electronic materials.
Multilayered polymers are being developed for use as
impermeable fi lms on fl exible screens and electr onic
devices, which must be protected from water and
oxygen.
Preliminary results on a melt processable glass
that can be incorporated into layered materials to
”
LAYERED
LAYERED
CENTER FOR LAYERED POLYMERIC SYSTEMS
LAYERED
C E N T E R F O R L AY E R E D P O LYM E R I C S Y S T E M S
LAYERED
POLYMERIC SYSTEMS
POLYMERIC SYSTEMS
POLYMERIC SYSTEMS
CENTER FOR LAYERED POLYMERIC SYSTEMS
POLYMERIC SYSTEMS
C E N T E R F O R L AY E R E D P O LYM E R I C S Y S T E M S
POLYMERIC SYSTEMS
TEAM SCIENCE • CENTER FOR LAYERED POLYMERIC SYSTEMS
We can take a polymer off the shelf
and do it—and we can make miles of
the stuff. None of this ‘little milligram
quantities’ and laborious synthesis
and worrying about scale-up.
“
We can take a polymer off the shelf
“
We can take a polymer off the shelf
KNOWLEDGE TRANSFER
LAYERED LENS TECHNOLOGY FOR
ADVANCED CAMERAS
Researchers at the center have taken inspiration from
nature in the development of nanolayered lenses that
are not unlike the lenses in the eyes of fi sh.
In fi sh lenses, the material’s ability to bend light,
or refractive index, gradually changes with depth
inside the lens: in other words, they have a refractive
index gradient. “We are able to copy that using the
nanolayer approach,” says center research chair Eric
Baer.
Lenses of this type exhibit a wider fi eld of view
with less aberration than conventional lenses having
no index gradients. The “gradient refractive index”
or GRIN lens shown in the fi gure below mimics a
segment of the octopus lens. It contains more than
500,000 nanolayers.
Baer notes that the technology is being
considered by public and private sector organizations
for use in advanced cameras.
Gradient Refractive
Index (GRIN) Lens
— CLIPS DIRECTOR ANNE HILTNER
60 CENTER FOR LAYERED POLYMERIC SYSTEMS • TEAM SCIENCE
