Research on
super-hydrophobic surfaces could
result in
cleaner, more efficient power
By Todd Hollingshead, BYU, May 21, 2014
In a
basement lab on BYU’s campus, mechanical engineering professor Julie Crockett
analyzes water as it bounces like a ball and rolls down a ramp.
This
phenomenon occurs because Crockett and her colleague Dan Maynes have created a
sloped channel that is super-hydrophobic, or a surface that is extremely
difficult to wet. In layman’s terms, it’s the most extreme form of water proof.
Engineers
like Crockett and Maynes have spent decades studying super-hydrophobic surfaces
because of the plethora of real-life applications. And while some of this
research has resulted in commercial products that keep shoes dry or prevent oil
from building up on bolts, the duo of BYU professors are uncovering
characteristics aimed at large-scale solutions for society.
Their
recent study on the subject, published in academic journal Physics of
Fluids, finds surfaces with a pattern of microscopic ridges or posts,
combined with a hydrophobic coating, produces an even higher level of water
resistance--depending on how the water hits the surface.
“Our
research is geared toward helping to create the ideal super-hydrophobic
surface,” Crockett said. “By characterizing the specific properties of these
different surfaces, we can better pinpoint which types of surfaces are most
advantageous for each application.”
Their work
is critical because the growing list of applications for super-hydrophobic
surfaces is extremely diverse:
- Solar
panels that don’t get dirty or can self-clean when water rolls off of them
- Showers,
tubs or toilets you don’t want hard water spots to mark
- Bio-medical
devices, such as the interior of tubes or syringes that deliver fluids to
patients
- Hulls
of ships, exterior of torpedoes or submarines
- Airplane
wings that will resist wingtip icing in cold humid conditions
But where
Crockett and Maynes’ research is really headed is toward cleaner and more
efficient energy generation. Nearly every power plant across the country
creates energy by burning coal or natural gas to create steam that expands and
rotates a turbine. Once that has happened, the steam needs to be condensed back
into a liquid state to be cycled back through.
If power
plant condensers can be built with optimal super-hydrophobic surfaces, that
process can be sped up in significant ways, saving time and lowering costs to
generate power.
“If you
have these surfaces, the fluid isn’t attracted to the condenser wall, and as
soon as the steam starts condensing to a liquid, it just rolls right off,”
Crockett said. “And so you can very, very quickly and efficiently condense a
lot of gas.”
The
super-hydrophobic surfaces the researchers are testing in the lab fall into one
of two categories: surfaces with micro posts or surfaces with ribs and cavities
one tenth the size of a human hair. (See images of each to the right.)
To create
these micro-structured surfaces, the professors use a process similar to photo
film development that etches patterns onto CD-sized wafers. The researchers
then add a thin water-resistant film to the surfaces, such as Teflon, and use
ultra-high-speed cameras to document the way water interacts when dropped, jetted
or boiled on them.
They’re
finding slight alterations in the width of the ribs and cavities, or the angles
of the rib walls are significantly changing the water responses. All of this
examination is providing a clearer picture of why super-hydrophobic surfaces do
what they do.
“People
know about these surfaces, but why they cause droplets or jets to behave the
way they do is not particularly well known,” Crockett said. “If you don’t know
why the phenomena are occurring, it may or may not actually be beneficial to
you.”
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