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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 | A P R I L 2 0 1 5
1 2 EMERGING TECHNOLOGY
MATERIAL CHANGES
COLOR ON DEMAND
Scientists at the University of Cal-
ifornia, Berkeley, created an incredibly
thin material that can change color on
demand by applying a small amount of
force. The novel material offers possi-
bilities for a new class of display tech-
nologies, color-shifting camouflage,
and sensors that can detect otherwise
imperceptible defects in buildings,
bridges, and aircraft. “This is the first
time anybody has made a flexible cha-
meleon-like skin that can change color
simply by flexing it,” says researcher
Connie Chang-Hasnain. By carefully
etching tiny features—smaller than a
wavelength of light—onto an extremely
thin silicon film, the team was able to
select the range of colors the material
would reflect, depending on how it was
flexed and bent. .
SHAPE-SHIFTING METAL
MIMICS TERMINATOR ROBOT
Researchers at Tsinghua Universi-
ty, China, report they have discovered a
way to mimic the shape-shifting robot
in the Terminator movies, at least in a
small way. The team was working with
gallium. After adding a small amount of
indiumand tin, a tiny piece of aluminum
was fixed to a single drop of the alloy
(to serve as fuel) and was dropped into
a container of either sodium hydroxide
or salt water. The drop propelled itself
around the container for about an hour.
In subsequent tests, the container was
shaped with channels and the drop fol-
lowed a predetermined path. Further,
if the drop encountered a part of the
channel that was slimmer than it was,
it could still squeeze through.
Closer analysis reveals that when
the drop is placed in the solution, a
charge imbalance occurs between the
drop’s front and back, causing a pres-
sure differential. As aluminum reacts
with salt water, tiny bubbles are formed
and serve to push the drop forward. The
experiments build on prior work, which
show that an electric charge can cause
a drop to both expand and change
shape with some liquid metals. This
could result in drops that not only move
themselves through liquids, but change
shape according to predetermined
needs. .
Artificial “skin” changes color as a small amount of force is applied. Courtesy of
The Optical Society.
Research from Tsinghua University could
pave the way to deliver materials through
pipes or even blood vessels using liquid
metal drops.
N1 Technologies Inc., Daytona
Beach, Fla., filed a patent for a
nano-engineered super glass called
TungstenGlass. It features high
impact and torsion resistance and
enhanced electrical properties,
and will initially target applications
in cell phones and other mobile
devices. The material is a boro-
silicate-based glass infused with
tungsten and carbon nanotubes.
.
BRIEFS
Two new projects underway at the Stanford Institute for Materials and
Energy Sciences (SIMES), Calif., could enable future electronic and pho-
tonic applications. SIMES is a joint institute of Stanford University and
DOE’s SLAC National Accelerator Laboratory. Both projects will explore
an emerging field called valleytronics, in which electrons move through
the lattice of a 2D semiconductor as a wave with two energy valleys whose
characteristics can be used to encode information. .