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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 | M A R C H 2 0 1 6
1 4 SURFACE ENGINEERING
SELF-HEALING SYSTEM
USES SECRETION
Researchers at Harvard Univer-
sity, Cambridge, Mass., developed a
new system of material self-healing
that uses a fluid secretion process in-
spired by biological wound healing.
The system consists of liquid droplets
inside a supramolecular polymer gel
with a thin layer of liquid on its surface.
When the surface liquid is removed or
depleted, the droplets spontaneous-
ly release only enough fluid to replace
what is lost on the surface. Current
fluid secretion technologies generally
use one-time-only release mechanisms
where fluid continues flowing at a con-
sistent rate until the supply is exhaust-
ed. Unlike these static models, the
new system is out of equilibrium, like
systems in nature, making it unstable
enough to respond to its environment.
The supramolecular polymers are
reversibly bonded to each other, mean-
ing they can detach to allow liquid to
filter through the matrix, then reattach
and adapt to the shrinking liquid re-
serves. When the system is cut down
the middle, the newly exposed polymer
surface signals droplets to secrete liq-
uid, quickly filling in the crack between
the ends of broken polymers. Over
time, polymer strands swim through
the liquid and stitch themselves back
together. The system even self-reports
its liquid levels: As fluid is secreted, the
gel becomes more and more transpar-
ent over time. .
NANOSTRUCTURED COATINGS
CLEAR THE AIR
Bozhidar Stefanov, a graduate
student at Uppsala University, Swe-
den, developed an improved method
for depositing nanostructured surface
coatings onto window glass used to
clean indoor air of organic pollutants.
Through a process called photocataly-
sis, these titanium dioxide coatings ab-
sorb ultraviolet light from the sun and
use that energy to destroy molecules of
pollutants in the air when it is passed
between two window panes. However,
Harvard scientists created a new
technology for fluid secretion and
self-healing behavior. Courtesy of
Jiaxi Cui and Joanna Aizenberg.
Window glass with a nanostructured
coating based on titaniumdioxide.
as pollutant decomposition products
bind to the coating surface and block
active sites, photocatalytic activity di-
minishes. To address this problem, Ste-
fanov adapted the industrial process of
magnetron sputtering to apply these
coatings.
Only about 10% of the crystalline
facets of titanium dioxide nanoparti-
cles are significantly photocatalytic,
so when nanoparticles are randomly
deposited, it is unlikely that a large pro-
portion of the film surface will be highly
reactive. Stefanov’s application process
increases the probability that very re-
active titanium dioxide facets are ex-
posed. These preferentially oriented
coatings exhibit higher activity against
air pollution, and their activity is less
dependent on external conditions such
as humidity and temperature.
GE Aviation, Evendale, Ohio, and
Praxair Surface Technologies
Inc., Indianapolis, formed a joint
venture for the development, sup-
port, and application of specialized
coatings. Formulas will be tai-
lored to current and future engine
models produced by GE Aviation
and CFM International, Cincin-
nati, including the GE9X and LEAP
engines.
.
BRIEFS
IHI Hauzer Techno Coating, the Netherlands, acquired the intellectual
property rights and trademarks for the Cromatipic ecological chrom-
ing system, formerly owned by Sidasa Engineering, Spain. Hauzer will
supply consumables to all Cromatipic users. The chroming system is an
environmentally friendly technology that can replace electroplating on
various plastic substrates and aluminum alloys. .