Tech Briefs Magazine - December 2021 - 23

Method Enables Wings to be De-Iced in Flight
The technique controls rather than combats ice formation.
Virginia Polytechnic Institute, Blacksburg
o control ice formation on a plane,
even when it's in flight, researchers
created a de-icing method that exploits
how frost grows on pillar structures to suspend
ice as it forms into a layer that's easier
to remove.
T
De-icing a plane at the airport prior to
takeoff is possible but planes also experience
plummeting temperatures and rapid
ice formation in flight. Once ice forms on
the wings, it can greatly inhibit a pilot's
ability to safely operate the aircraft.
Equipping planes with the ability to
remove ice while flying at altitudes
between 35,000 and 42,000 feet would provide
a better set of tools to maintain safety.
The team worked from the knowledge
that water droplets behave in different
ways, depending on the surface. They
aimed to leverage a principle known as
Cassie's Law, which shows that air can be
trapped under water drops if the drops are
suspended atop a structure that is bumpy
and water-repellent. With a structure that
could trap air underwater in this " Cassie
state, " the team sought to make ice form in
a layer with lower adhesion to the surface.
Making a surface water-repellent typically
requires a chemical coating that
must be periodically replenished and the
bumpy surface also tends to wear over
time. The team opted to make a waterrepellent
surface that doesn't require
fragile chemical coatings or ultra-fine
bumps. Instead, they developed a simple
and durable structure in the form of aluminum
millimeter-sized pillars.
The team created an array of pillars,
each 1 millimeter tall by 0.5 millimeter
wide. The tiny pedestals were machined
into a pattern with 1 millimeter be tween.
As the temperature dropped, frost preferentially
grew on the tops of the pillars,
resulting in elevated frost tips. As more
water was added, it was absorbed into this
porous frost layer. When water drops were
subsequently impacted on the surface,
they were caught on the frost pedestals.
These freezing drops created tiny " ice
bridges " that sealed the gaps of air in the
valleys between the frost-tipped pillars.
The water drops were caught by the frost
tips, building ice bridges to trap air pockets
underneath. Over time, a continuous
and air-trapping ice canopy formed over
the frost-tipped pillars. Whereas other
de-icing methods may still allow a sheet
of ice to adhere more directly to a large
surface area, these trapped air gaps
cause the sheet to be suspended, lowering
the amount of adhesion ice has to
the surface.
Using larger pillars in place of nano -
structures and frost tips in place of a
hydrophobic coating, the team realized
the same benefit of trapping air underneath
the forming ice while avoiding
durability concerns. With a weaker
bond, it's possible to use the air pockets
to then push ice away.
For more information, contact Emily
Roediger at eroedig@vt.edu; 540-231-2108.
Tech Briefs, December 2021
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Tech Briefs Magazine - December 2021

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