These Liquid-Repelling Materials Defy Nature’s Design, Here’s How

I remember watching this video online and
being mesmerized. The more liquid they spilled on the items
the more I thought “how was this even working?, what’s going on here?” This is a superhydrophobic coating with properties
that are seemingly impossible. But this material science field is making
some exciting developments with materials that are even more impressive, and omniphobic. You might have heard of a term called hydrophobic,
which can mean you’re really scared of water, but in this case we’re talking about an
object being extremely water repellent. You might see this with water on a nonstick
cooking pan when it beads up and rolls around with ease. But surfaces can not only be only hydrophobic,
but omniphobic, meaning virtually any kind of liquid, from water to oil can slide off
a surface with ease. Which isn’t material you’d find in nature. The applications for a property like this
are endless. They could help with the day to day cleaning
of your house, make electronics water resistant, could help ships glide through water faster
and even help heat transfer at nuclear power plants. Reasons like these are probably why scientists
have spent years trying to get it right. Soo what’s the hold up? Well let’s start with the fact not all liquids
are the same and they have different surface tensions, which causes them to interact with
materials differently. Let’s take water for example. Inside the liquid, there are intermolecular
attractive forces at play, meaning the water molecules want to cling together. But when there are dissimilar molecules above
them, like air for instance– those cohesive forces help the water molecules bond stronger
with their neighbors – creating a thin “barrier” of sorts. This is the phenomenon that creates droplets,
and help water bugs stay afloat. But like I mentioned before, this surface
tension changes from liquid to liquid. Water has a very high surface tension whereas
oil has a very low surface tension, so it seeps into everything. So knowing that, material scientists have
created nanostructures made of small pillars spaced out just enough so that liquid can
sit on small pockets of air. That way the liquid’s own surface tensions
lifts it up, causing all of these beads and droplets to form. And it totally works! Buut it relies on every pillar being perfect
and this structure is only as strong as its weakest link. If one pillar breaks, the liquid can seep
through the air pockets and there goes all your omniphobicity. And just to keep things more complicated,
the materials also have to withstand condensation. If water vapor makes its way into the pockets
within the omniphobic structure, it can condense into liquid and destroy repelling properties. This has been one of the biggest hurdles that
material scientists have tried to overcome. And now researchers at MIT are tackling this
problem head on, They’ve used nanotechnology to create not only microscopic, but condensation-resistant
“T” shaped structures. The difference between this new development
and earlier studies is that they made the air pockets disconnected, rather than connected. The disconnection would prevent a liquid from
penetrating a single air pocket and spreading throughout the whole material, which helps
with the issue of condensation! They’ve nailed a proof of concept, but they
still need more work to bring it into market. But MIT isn’t the only team working on omniphobic
materials. A US Navy funded project from the University
of Michigan made an omniphobic coating. Instead of building it, the material can be
sprayed on. And as far as durability and clarity goes,
it’s one of the best coatings yet. Typically, researchers mix together a filler,
giving it repelling properties, and a binder, giving it durability. But that doesn’t always work, instead the
team focused on a property called “miscibility”. They did mathematical calculations of the
properties of many chemical substances in order to predict the best solution. And it worked. Their coating is clear, durable, can be applied
to numerous surfaces and sheds just about any liquid. They’re hoping it could last up to a year. Which sounds like a good goal since they’re
interested in putting it on naval ships to reduce drag and save on fueling cost. However, some of the chemicals they used might
not be the safest and they want to reformulate so they’re nontoxic and more commercially
viable. They have a goal to get the coating out in
the next year or two, so we’ll keep a lookout. It’s almost a race of who will create the
perfect omniphobic innovation, but regardless who gets there first, the real winner will
be us, reaping the benefits of decades of work like we always do and it’s going to
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dot com. One last fun fact before you go, The MIT design
is so nice to look at because the periodic, nanoscale features on the surface diffract
light, causing the colors in the image. If you love material sciences like this then
go ahead and subscribe. And don’t forget to watch this video about
how we’re making these even stranger materials better for electronics. Thanks so much for watching!

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