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Carbon Nanotubes -- cylindrical molecules
that consist of rolled-up sheets of single-layer
carbon atoms, the same basis for graphene
-- goes back to 1991, which, weirdly, is long
before the discovery of how to isolate graphene
itself.
The appeal of Carbon Nanotubes is their potential
to dramatically improve energy storage and
renewable energy... a topic that scientists
have been attempting to tackle for decades.
As it turns out, Carbon nanotubes can be easily
mass-produced already, so why haven’t we
seen the carbon nanotube revolution yet?
Will they really be game changers?
I’m Matt Ferrell … welcome to Undecided.
In the early 2000’s, Carbon Nanotubes were
all over the media, touted as being a breakthrough
in energy potential and a solution for what
sounded like endless applications.
Everything from composite materials for large
metallic parts like bikes, boats, and cars,
to highly efficient transistors, nano-inks,
bio tech, and even space elevators.
But after years of expected market roll-outs,
carbon nanotubes still haven't made the splash
in the tech world that they had promised.
As usual, the hype set expectations too high
... almost as high as the space elevator ... so
excitement dampened as time went on.
But the key problem wasn’t production of
Carbon Nanotubes themselves -- that had been
available long before -- instead it was with
the precision and separation of the different
types during manufacturing.
To understand that, let's take a step back.
Carbon nanotubes are essentially molecular
sheets of carbon atoms, also known as graphene,
which are arranged in a hexagonal lattice
or honeycomb arrangement – a bit like chicken
wire.
These sheets are organized in layers and manipulated
into a cylindrical shape.
So basically, graphene is the basis for Carbon
Nanotubes.
You can't have Carbon Nanotubes without graphene.
Now, these nanotubes can be designed and arranged
in many ways:
* Single-Walled Carbon Nanotubes (SWNTs) are
made of, as you might imagine, a single layer
of graphene.
The way in which they are rolled can impact
their conductivity.
I'll get to that in a minute.
* Multi-Walled Carbon Nanotubes (MWNTs) are
an extension of Single-Walled.
They're made-up of multiple layers of graphene
which better insulates their thermal and chemical
properties compared with Single-Walled tubes.
* Double-Walled Carbon Nanotubes (DWNTs) are
a combination of Single-Walled and Multi-Walled
- with thermal, chemical and conductivity
properties that are intermediate compared
to the other two.
Depending on how the hexagonal lattice is
rolled, it affects what's called the chiral
angle of the final tube.
It's how that hexagonal pattern spirals along
the tube.
If you follow the pattern across the diameter
of the tube, you'll see three basic types:
armchair, zig-zag, and chiral nanotubes.
The orientation can make it act as either
a metallic or semiconducting material.
When manufacturing nanotubes, you usually
end up with a mixture of types.
The nanotubes have a tendency to clump into
an entangled mess.
And separating them apart has been the big
challenge for mass-scale manufacturing.
Remember, they’re only a few nanometers
in diameter, or about 50,000 times smaller
than the width of a human hair.
It's only when Carbon Nanotubes are grouped
by purity, metallic or semiconducting, that
they can be used effectively ... which will
ultimately advance all of those big promises
that were made.
Over the past few years there have been some
breakthroughs on how to effectively isolate
carbon nanotubes after manufacturing, which
has helped to push Carbon Nanotubes back into
mainstream technology.
Researchers at McMaster University adapted
a polymer process, which had been popularly
used to reduce carbon nanotubes to only metallic
components.
The problem with that process was that it
dissolved and washed away the semiconducting
nanotubes.
The researchers found a way to reverse the
process, leaving semiconducting nanotubes
behind and intact.
A team of researchers from Northwestern University
used the common chemical, cresol, to isolate
nanotubes.
Some methods use chemicals and chemical reactions
to modify the nanotubes to force them to separate,
but that can sometimes leave a residue that
alters their abilities.
When they used cresol they not only separated
the nanotubes, but formed them into a thick,
moldable gel.
As one of the researches pointed out:
> "Essentially, this solvent system now makes
nanotubes behave just like polymers..."
> "It is really exciting to see cresol-based
solvents make once hard-to-process carbon
nanotubes as usable as common plastics."
-Jiaxing Huang
It’s these types of breakthroughs that are
going to take us from bulk manufacturing,
all the nanotube types tangled together, to
isolated mass-scale manufacturing of Carbon
Nanotubes.
If we’re ever going to make that space elevator,
we’re going to need A LOT of isolated nanotubes.
But where does that leave us with actual products
that we may see in our daily lives not too
far from now?
There are a lot of examples to pull from in
just the past few years.
One recent one is Vantablack, which is one
of the darkest materials on the planet, absorbing
up to 99.965% of visible light.
Developed by Surrey NanoSystems in the UK,
VANTA stands for Vertically Aligned Nanotube
Arrays.
It’s that alignment that traps light that
hits the surface from bouncing back out, which
makes it look like a deep, dark void.
It may not seem like it has a lot of value,
but it can have a big benefit for keeping
stray light from entering a telescope and
improving the performance of infrared cameras.
On a less practical level, I don’t know
about you, but I’d love to see a car painted
with this in person.
Just this June, MIT researchers demonstrated
how commercial silicon-based transistor foundries
could transition to carbon nanotube transistors,
and save an immense amount of time.
The fabrication process is up to 1,100 times
faster than today’s silicon process.
Part of the reason for that is silicon transistors
are manufactured at around 450-500 degrees
Celsius, but carbon nanotubes can be manufactured
at room temperatures.
This will allow for the layering of circuits
for a three-dimensional chip since you can
build right on top of a previously fabricated
layer.
If you tried that with silicon process you’d
melt the previous layer.
3D chip designs are expected to outperform
2D versions.
But one of the more active areas for Carbon
Nanotubes research is around solar panels,
and there's been a lot of interesting advances
there.
Just last year Rice University had two interesting
advancements.
One team of researches showed that double-walled
nanotubes could have a dramatic impact on
solar panel efficiency because of the double-wall’s
efficiency at separating positive and negative
charges to create current.
Another team has come up with a method to
improve solar panel efficiency by up to 80%.
The fascinating part of this discovery is
not that the nanotubes are actually improving
the panel efficiency directly, but more in
how it helps to capture unused potential ... heat.
To be more specific, infrared heat from the
sun.
Current panels are only capturing light and
converting that into electricity.
The research team designed an array of cavities
patterned into a film of aligned carbon nanotubes.
They’re able to absorb and channel thermal
photons and emit them as light ... essentially
converting heat into a form that solar panels
can then convert into electricity.
Related to heat is another innovation that
came up just recently.
You may be aware that solar panels lose efficiency
when they're too hot.
Well, researchers at the King Abdullah University
of Science and Technology (KAUST) have come
up with a system that keeps panels cool with
no moving parts or excess energy drain.
In their project, KAUST researchers developed
a polymer that contains calcium chloride.
When the material is exposed to humid air
it absorbs the moisture and expands in size.
In the latest research they combined that
polymer with carbon nanotubes to reverse that
cycle and release the trapped water.
When the gel was applied to the back of a
solar panel, it’s able to absorb moisture
from the humid air at night and then slowly
release it during the hottest parts of the
day.
The team saw panel temperatures reduced by
10 degrees Celsius, which improved efficiency
up to 20%.
But this doesn’t just apply to solar panels.
Renyuan Li, one of the researchers, said:
“We believe this cooling technology can
fulfill the requirements of many applications
because water vapor is everywhere and this
cooling technology is easy to adapt to different
scales.”
”The technology could be made as small as
several millimeters for electronic devices,
hundreds of square meters for a building,
or even larger for passive cooling of power
plants.”
-Renyuan Li
Another area where we’re seeing carbon nanotube’s
making an impact is energy storage.
The French company, Nawa, has created an ultracapacitor
that’s going into mass production.
While batteries, like lithium ion, offer far
more specific energy storage, they charge
and discharge far slower than ultracapacitors.
Capacitors can charge and discharge in an
instant, so they’re perfect for quick bursts
of huge power.
They can also last for a million charge cycles.
But again, the downside is the amount of energy
they can store, and for how long.
Nawa’s new ultracapacitor sits somewhere
in between a capacitor and battery.
It can store about 5 times more energy than
competing ultracapacitors, but charges in
seconds.
It’s using vertically aligned carbon nanotubes
that are grown with a patented method for
coating two sides of aluminum or copper foil.
Some of the first places they see this technology
getting used is in power tools, automated
vehicles in factories and warehouses, and
electric vehicles.
All areas that require high energy use with
limited charging downtime.
The team at the Advanced Materials and BioEngineering
Research Center (AMBER) at Trinity College
in Dublin, have created a carbon nanotube
composite electrodes for use in lithium ion
batteries.
They’re able to build cells with a specific
energy of 480 Wh/kg, which is around twice
of a normal lithium ion cell.
Companies like Nokia Bell Labs, which is a
partner of the research center, are interested
in the breakthrough for powering 5G phones
and the broader network with more efficient
batteries.
But this type of breakthrough could easily
make an impact in grid storage and electric
cars as well.
Carbon nanotubes may have fallen out of the
limelight for a while, but there has been
a lot of interesting advances over the past
few years that’s reigniting interest.
In my case, I’m really excited to see how
the advancements impact solar and energy storage.
But as cool as some of this is, we’re still
not getting a space elevator anytime soon.
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