Tech Briefs Magazine - November 2021 - 12

Rugged, Reliable,
Proven Differential
Measuring Systems
for Aerospace
Q & A
Self-Healing Polymers Create WaterResistant
Coatings
Jingcheng Ma, along
with a team of researchers
at the University of Illi -
nois, Urbana-Champaign,
found a way to make ultrathin
water-resistant surface
coatings robust enough to
survive scratches and dings.
Tech Briefs: What got you started
on this project?
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Jingcheng Ma: This is something that
many people have tried before - to
develop a thin hydrophobic (water-resistant)
coating for the condenser of a steam
power plant to enhance its energy efficiency.
Most previous ultrathin coatings
have developed pinhole defects once they
cured onto a surface. Steam penetrates
through these defects, leading to gradual
delamination. We wanted a coating that
would not develop these defects.
Tech Briefs: Why do hydrophobic
coatings help heat transfer?
Ma: In every steam power plant, liquid
water is heated and becomes steam to
drive a turbine. Then it cools down in the
condenser and returns to liquid. This
condenser is very important to the overall
efficiency of the cycle. So, we wanted to
make the vapors condense more quickly
and leave more quickly so that the heat
can transfer from the steam to the condenser
at a faster rate, which translates to
higher energy efficiency.
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Tech Briefs: How does a coating
achieve that?
Ma: The materials used in these condensers
are metals, like copper or aluminum,
because they're robust, they conduct
heat very quickly, and they're relatively
cheap. But since these surfaces attract
water, when you condense the steam, liquid
films form on them. The liquid film is a
thermal barrier, which impedes the heat
transfer from the vapor to the metal.
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Removing the film enhances the heat transfer
coefficient of the steam power plant.
Tech Briefs: What makes the coating
self-healing?
Ma: Polymers have lots of molecular
chains packed together. If you scratch the
surface, you make a pinhole in it - you
break the network. In this material, we
add a relatively active component: boric
acid. When you break this network, the
boric acid restarts a connection between
different molecular chains so that it just
heals and you have another network.
Tech Briefs: What are some other
uses for the coating?
Ma: Anti-icing, anti-fogging, anti-bacterial,
anti-fouling - all these rely on
the nature of the hydrophobic surface.
For example, anti-icing basically means
if you have ice on a surface like an airplane
wing, it can be removed more easily
because the hydrophobic surface doesn't
like water, so it doesn't like ice as well.
Anti-fouling doesn't rely on the surface
being hydrophobic but if you have a pinhole-free
surface, you don't have corrosion
because you don't have charge transfer
between the corrosive environment
and the substrate. This creates a perfect
barrier for protecting the materials
beneath the coating.
Tech Briefs: What future questions
do you intend to explore?
Ma: Our film - commonly called a
vitrimer - is thinner than 10 nanometers,
and is completely different from previous
research, which was done on bulk
materials one centimeter by several millimeters
high, which you can see using
the naked eye. You can apply our material
not only to large plain surfaces, but also
to nanomaterials. You can modify the surface
properties of these smaller objects.
Read the full transcript of this Q&A at
www.techbriefs.com.
Tech Briefs, November 2021
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Tech Briefs Magazine - November 2021

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