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It’s basically right out of a spy movie: a glider swoops into enemy territory at night,
lands with some sort of secret message or item, and then vanishes without a trace in
the pink light of dawn.
“Now where did this come from?”
our unwitting villain says, bending down to pick it up…
Okay, okay, I might be getting overexcited.
But as of this week, a disappearing plane could really exist.
At a meeting of the American Chemical Society, researchers announced that they have created
a material that vaporizes in sunlight.
It’s all thanks to the incredible power of chemistry.
The material is a polymer known as polyphthalaldehyde or PPHA.
Polymers are like chains.
They’re big molecules made up of many repeated smaller units chemically bonded together.
Each link in the chain is held together by one or more chemical bonds, and under the
right circumstances, those bonds start to come apart and the whole chain can disintegrate.
But when that happens is dependent on the particular polymer and what’s known as its ceiling temperature.
Below that, the polymer wants to stay a polymer.
Above it, it will start to break down into its component pieces, called monomers.
For instance, good old polystyrene — sometimes known as Styrofoam — has a very high ceiling temperature.
Which is why the stuff hangs around in landfills basically forever.
PPHA has a low ceiling temperature.
You break one bond at room temperature and the whole thing breaks down almost instantly.
So the challenging part is actually keeping it from vanishing before you want it to.
Luckily, the research team found a way to remove more of the catalyst that helps build
the polymer in the first place, which gives it a much longer shelf life.
They also used a cyclic version of PPHA rather than a linear one, which is more stable because
it doesn’t have any loose ends where the unraveling process can start.
And then… they just started experimenting.
They added a light-sensitive compound to it to get it to start the self-destruction process on cue.
It produces a strong acid when it encounters UV light, which then attacks the polymer’s bonds.
Once one bond breaks, the PPHA has loose ends again and disintegrates in 5 to 7 minutes
— as long as the ambient temperature is above PPHA’s ceiling temperature of -40˚C
Then they found photosensitive catalysts that worked at different wavelengths of light,
so that indoor light or different colors could be used to trigger the self-destruct.
And they added a liquid plasticizer to the material, so that they could have both rigid
and bendy structures to build things with, like, planes and parachutes.
They even built in a time-delay function.
By having the catalyst produce a weaker acid, they found they could have a longer gap between
light exposure and when the structure self-destructs.
And they’re not done yet!
While PPHA itself vaporizes completely, the plasticizer does leave behind a liquid residue,
so that’s something the team is working on solving.
The researchers also hope that the materials can be used for all sorts of purposes in the
future, like no-waste sensors for environmental monitoring.
So they’re going to keep tinkering to see what other kinds of special features they
can build into their PPHA.
Speaking of things that sound made up by Hollywood, scientists can apparently doll out night vision now.
Using nanoparticles!
Injected into your eyes!
Well, not your eyes.
Not quite yet.
But scientists have given infrared supervision to mice, and according to a talk they gave
at the American Chemical Society meeting this week, they are interested in doing it with
other mammals and maybe, someday, with people.
Without night-vision goggles, mammals can only see light in what’s known as the visible
spectrum — wavelengths of about 400 to 700 nanometers.
Near-infrared light is beyond the red end of the spectrum.
And it’s what night-vision goggles that use thermal imaging look for, because it’s
emitted by warm objects.
That means that if we could see it, it would let us see things that give off heat even in total darkness.
So, to make infrared light visible to us, the researchers developed specialized nanoparticles
known as upconversion nanoparticles or UCNPs, which had a core made mostly of the rare-earth
elements erbium and ytterbium.
When these elements absorb infrared light, they emit visible green light, basically converting
the invisible light into something mammalian brains can make sense of.
The team got these nanoparticles to stick to light-sensing cells by adding a protein
that attaches to certain sugars.
Then, all they had to do was inject the nanoparticles into the eyes of their mouse test subjects.
Ten weeks later, the mice weren’t just fine — they could see near-infrared light.
For example, mice trained to expect a shock when they saw green light would also freeze
when they saw infrared light because the nanoparticles were converting it to green light inside of their eyeballs.
And in a swimming task, mice with the infrared vision were able to locate a platform they
could stand on in the dark.
Mice without the UCNPs couldn’t find it.
Now, exciting as all that is, we’re probably still a ways away from injecting this stuff
into human retinas.
But!
The researchers have made steps towards making them more human-friendly, including finding
an organic substitution for the rare-earth elements in the UCNPs.
These don’t only make the nanoparticles a bit more biocompatible, they also improve
the tech by making the transformed light brighter.
And in addition to basically giving people superpowers, the researchers also imagine
the tech being used to deliver infrared-triggered doses of medication directly to the photoreceptors of the eye.
But there are a lot of regulatory hurdles that would need to be cleared before we get there.
For now, I guess we’ll all just have to be jealous of these mice.
It’s like maybe the one time being our favorite lab animals has really paid off for them,
so… let’s let them have this one.
Thanks for watching this episode of SciShow News!
And especially thank you to today’s President of Space, Matthew Brant.
Matthew, we really appreciate your continued support!
In fact, here’s a special space salute!
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