Imagine tiny cracks in your patio table healing by themselves, or the
first
small scratch on your new car disappearing by itself. This and more may
be possible
with self-healing coatings being developed at the University
of Illinois.
 |
| Illinois researchers Paul Braun, right, and Scott White have created self-healing coatings that automatically repair themselves and prevent corrosion of the underlying substrate. (Credit: Photo by L. Brian Stauffer) |
The new coatings are designed to better protect materials from the effects
of environmental exposure. Applications range from automotive paints and
marine
varnishes to the thick, rubbery coatings on patio furniture and park
benches.
"Starting from our earlier work on self-healing materials at the
U. of
I., we have now created self-healing coatings that automatically repair
themselves
and prevent corrosion of the underlying substrate," said Paul Braun, a
University Scholar and professor of materials science and engineering.
Braun
is corresponding author of a paper accepted for publication in the
journal Advanced
Materials, and posted on its Web site.
To make self-repairing coatings, the researchers first encapsulate a
catalyst
into spheres less than 100 microns in diameter (a micron is 1 millionth
of a
meter). They also encapsulate a healing agent into similarly sized
microcapsules.
The microcapsules are then dispersed within the desired coating material
and
applied to the substrate.
"By encapsulating both the catalyst and the healing agent, we have
created
a dual capsule system that can be added to virtually any liquid coating
material,"
said Braun, who also is affiliated with the university's Beckman Institute,
Frederick Seitz Materials Research Laboratory, department of chemistry, and
Micro and Nanotechnology Laboratory.
When the coating is scratched, some of the capsules break open,
spilling their
contents into the damaged region. The catalyst and healing agent react,
repairing
the damage within minutes or hours, depending upon environmental
conditions.
The performance of the self-healing coating system was evaluated
through corrosion
testing of damaged and healed coated steel samples compared to control
samples
that contained no healing agents in the coating. Reproducible damage was
induced
by scratching through the 100-micron-thick polymer coating and into the
steel
substrate using a razor blade. The samples were then immersed in a salt
solution
and compared over time.
The control samples corroded within 24 hours and exhibited extensive
rust formation,
most prevalently within the groove of the scratched regions, but also
extending
across the substrate surface, the researchers report. In dramatic contrast,
the self-healing samples showed no visual evidence of corrosion even
after 120
hours of exposure.
"Our dual capsule healing system offers a general approach to
self-healing
coatings that operates across a broad spectrum of coating
chemistries,"
Braun said. "The microcapsule motif also provides a delivery mechanism
for corrosion inhibitors, antimicrobial agents, and other functional
chemicals."
With Braun, the paper's co-authors are U. of I. aerospace engineering
professor
and Beckman researcher Scott White, and former Beckman and materials
science
graduate student Soo Hyoun Cho. A company formed by Braun, White and
other U.
of I. researchers is exploring commercialization of the self-healing
coatings
technology.
The work was funded by Northrop Grumman Ship Systems, the U.S. Air
Force Office
of Scientific Research, and the Beckman Institute.
Posted December 10th, 2008
