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A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 1 5
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EMERGING TECHNOLOGY
NANOSTRUCTURES SELF-
ASSEMBLE, SELF-DESTRUCT
Materials that can self-assemble
and self-destruct once their work is
done are highly advantageous for a
number of applications, such as com-
ponents in temporary data storage
systems or for medical devices. For ex-
ample, such materials could seal blood
vessels during surgery and reopen
them later. Andreas Walther, research
group leader at DWI-Leibniz Institute
for Interactive Materials, Germany, de-
veloped an aqueous system that uses
a single starting point to induce self-
assembly formation, whose stability is
preprogrammed with a certain lifetime
before disassembly occurs without any
additional external signal.
A closed system was developed,
in which the precise balance between
assembly reaction and programmed
activation of the degradation reaction
controls the lifetime of the materials.
A single injection initiates the process,
which distinguishes this new approach
from current responsive systems that
always require a second signal to trigger
the disassembly. Then, pH changes are
used to control the process. The reac-
tion is initiated by the addition of a base
and a dormant deactivator. This rapid-
ly increases the pH and the building
blocks—block copolymers, nanoparti-
cles or peptides—which assemble into
a 3D structure. At the same time, the
pH change stimulates the dormant de-
activator. Currently, a hydrolytic reac-
tion is used to activate the deactivator.
However, the team is already working
on more sophisticated versions, which
include an enzymatic reaction to slowly
start the self-destruction mechanism.
www.dwi.rwth-aachen.de.ENHANCING LIGHT EMISSION
IN MOLYBDENUM DISULFIDE
Molybdenum disulfide is a prom-
ising new material, but its best as-
set—monolayer thickness—is also its
greatest challenge. MoS
2
’s ultrathin
structure is strong, lightweight, and
flexible, making it a good candidate
for many applications, such as high-
performance, flexible electronics. Such
a thin semiconducting material, howev-
er, has very little interaction with light,
limiting its use in light emitting and ab-
sorbing applications.
“The problem with these materi-
als is that they are just one monolay-
er thick,” says Koray Aydin, assistant
professor of electrical engineering and
computer science at Northwestern
University’s McCormick School of Engi-
neering, Evanston, Ill. “So the amount
of material that is available for light
emission or light absorption is very lim-
ited. In order to use these materials for
practical photonic and optoelectric ap-
plications, we needed to increase their
interactions with light.”
Aydin and his team designed and
fabricated a series of silver nanodiscs
and arranged them in a periodic fash-
ion on top of a sheet of MoS
2
. Not only
did the nanodiscs enhance light emis-
sion, but the specific diameter of the
most successful disc, which is 130 nm,
was also discovered. Using the nano-
structures instead of a continuous film
to cover the MoS
2
allows the material to
retain its flexible nature and mechan-
ical properties. With enhanced light
emission properties, MoS
2
could be a
good candidate for light emitting diode
technologies. The next step is to use the
same strategy for increasing the light
absorption abilities to create a better
material for solar cells and photodetec-
tors.
northwestern.edu.
Scientists at DWI-Leibniz Institute
for Interactive Materials can pro-
gram self-assembly, lifetime, and
degradation of nanostructures con-
sisting of single polymer strands.
Courtesy of Thomas Heuser/DWI.
Silver nanodiscs on a sheet of monolayer
molybdenumdisulfide.
BRIEF
NASA
selected three proposals to develop and manufacture ultra-lightweight materials for future
aerospace vehicles and structures, which aim to reduce the mass of spacecraft by 40% percent for
deep space exploration. The awards include
HRL Laboratories LLC,
Malibu, Calif.: Ultralight
Micro-truss Cores for Space Launch Systems;
ATK Space Systems LLC,
Magna, Utah: Game Chang-
ing Technology Development Program Ultra-Light Weight Core Materials for Efficient Load Bearing
Composite Sandwich Structures; and
Dynetics Inc.,
Huntsville, Ala.: Ultra-Lightweight Core Mate-
rials for Efficient Load-Bearing Composite Sandwich Structures.
nasa.gov/spacetech.Image courtesy of NASA.