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JULIA GREER: I'm Julia Greer, as [INAUDIBLE] introduced me.
Thank you very much for that.
And I'd like to share with you a little bit about the three
dimensional architected structural meta-materials.
That's a mouthful.
So $245 million are spent each year in the US
to operate and produce airplanes.
Now, these airplanes weigh about 970,000 pounds.
So the majority of that cost comes from the amount of fuel
that's used to propel a machine like this through the air.
Now, at almost $3 per gallon and at about five gallons per mile,
you can do the back of the envelope calculation
to show that about $107,000 are spent
on a single flight from Los Angeles to Zurich, for example.
It was a really, really last minute ticket.
So if you look at all of these large construction structures,
you can see that, for example, the airplane is really heavy.
You can see that the bridge over here that I'm showing
is very expensive, because it's a tremendous amount
of construction materials that need
to go into its construction.
What I'm showing you here is the batteries in a car, in a Tesla,
for example, that are heavy and unsafe.
And then also, all of these will fit together eventually.
The artificial bones over there, they're not durable.
So what all of these have in common is the following.
For centuries, we've been operating in this regime
where the strength and the density are linked together.
Very much intimately coupled.
So what that means is that materials that are very strong,
and that means that they are high on the strength axis here,
they're also very, very heavy.
And so these are all the materials
that we already know how to make today.
Now, the materials that are very lightweight,
and that would be in the very low density regime,
are also weak.
So what do we do?
How do we make materials that are light weight, which
is what you want-- so that would be down here-- but also
at the same time are very, very strong, if everything that we
already know how to make is already plotted on here?
So what I'd like to do for my moonshot here is I'd
like you to imagine a world where the next generation
airplanes are just as powerful as they are today,
but they weigh as little as a toy airplane.
Or imagine a world where you have
this car that you drive home, and then when you get home,
it's light enough where you would put it on the roof.
I don't know why you would want to put a car on the roof,
but you'd put it up somewhere.
And the last example I'd like to show you
is imagine a world where the Golden Gate
Bridge, or any bridge that you'd like to construct,
the entire overall amount of materials
that are used for this construction
could fit in the palm of your hand.
And this sounds a little bit like science fiction, right?
Well, we think that we figured out
a way how we possibly can bring this world closer to reality.
And what I'd like to do now is to show you how.
So what we do is we combine the concepts
of architectural design, material science,
and nanotechnology to introduce the concept of architecture
into the material creation.
So imagine a monolithic stainless steel sheet
that you would normally use for construction.
And now imagine that steel sheet being
comprised of tiny, tiny little elements.
Thousands, maybe even millions of nanosized little elements,
such that they contain about 99% air.
Now, that's a very lightweight structure, right?
But how do we preserve the strength?
And so what I'd like to show you is that at the nano scale,
in these very, very small materials, what you can do
is get this so-called "smaller is stronger" effect.
For example, if this is some kind of strength and this is
some kind of [? feature ?] size, where you can see--
and this is a [INAUDIBLE] [INAUDIBLE] [? plot ?],
which means it's a power [? law-- ?] you can see that
materials actually get stronger when you make them smaller.
So in these nano architected materials
that I'd like to introduce to you,
we're capitalizing on both effects-- the nano materials
effect and the architectural effect
to create materials that are both lightweight and strong.
And what I'd like to show you are some of these nano-trusses
that we've been making in our group.
These are actual materials that were made in our group.
And we call them nano-trusses.
So I'd like to show you that the part in the middle here,
that's a computer design.
This is a CAD design that my students created.
And then everything else that you see here
has actually been made in my group.
And you can see how they get very close to one another
at these scales.
There are different geometries that we can write.
We can make them be almost any size that you want,
and we can make them out of almost any material
that you may want.
And what I'd like to show you now
is a video for how we would measure
their mechanical properties.
So we're actually compressing this material, as you see,
right in situ.
So you can actually observe we're
doing all of this inside of an electron microscope.
So we're compressing one of these lattices.
This is a hollow alumina matrix nano-truss,
and you can see that it totally recovers.
I'd like to play this movie for you one more time, because this
is actually-- so we all know what alumina is, right?
It's like chalk, brittle ceramic.
And what we're showing you here is
that not only is not breaking, but that you can compress it,
and it's still relatively stiff and strong
and that it recovers after we compressed it to about 50%
strength.
So these materials are also able to absorb energy.
So there's a lot of room for improvement in our material
design.
So let's go back and revisit this property space
that I was showing you before.
So if this is strength and this is density,
these are all the materials that we know how to make today.
There's actually a theoretical maximum that we can hit.
So you can, in fact, explore this very region, the target
region.
And that's the untapped white property space.
Where we can make materials that are both really,
really lightweight and very, very strong.
And we think we can do this by architecting these materials.
I'd like to spend a little bit of time describing to you how
we make them, because maybe you can't tell just
by looking at this.
So we begin with the CAD design.
As I showed you, this is a three dimensional structure.
It doesn't have to be periodic, this particular one that I'm
showing you happens to be a three-dimensional periodic
lattice.
And we do this by using this instrument called the two
photon lithography instrument.
So what it does is it focuses constructively
the interference of two different photons from two
different lasers, and it writes, it rasters this voxel
in three-dimensional space in whatever configuration
that you want that you specified in your CAD design.
So that's what we are systematically showing here.
Now, you create this out of a polymer.
So everywhere where this voxel travels,
it cross links the polymer.
Everywhere where it doesn't, it dissolves it away.
And so you end up with this polymer skeleton.
But now I told you that we can maybe build airplanes out
of these someday, right?
You don't build planes out of polymers.
So we really need to somehow deposit a different material
onto it.
And so this is what we do.
We actually use either sputtering,
or there are other deposition techniques
that we have available in our lab,
to deposit the rigid material of interest
on top of this polymer scaffold.
And that happens conformally in such a way that every truss
member is actually coated with this rigid material.
So now we have effectively a composite, right?
We have something rigid covering something that's polymeric,
and so it's relatively compliant.
Which we may not necessarily want.
So what we do after that is we actually cut off the edges,
and then we expose the internal polymer and we etch it way.
And so what you're left with is a structure
that, in itself, embodies every single scale from nanometers
up all the way to the centimeters.
And so the wall thickness-- I told
you these are hollow-- the wall thicknesses here
are on the order of nanometers.
So you can really utilize the smaller, stronger,
or any kind of nano-sized effect.
But at the same time, you're proliferating it
into a larger structure, so you can really
start constructing various materials out of this.
And so now what you may ask, what everyone should be asking,
is this is great, but how do you scale this up?
How do you actually make useful materials out of these?
Right now, this is all done at the lab scale in my group,
but we think that there might be a way
to utilize maybe something like roll-to-roll processing
or three-dimensional printing where we can really
start producing these sheets.
The most time-consuming step in creating these
is going in depth.
And so if we can make the sheets that are maybe three or four
unit cells tall, but have a wide lateral extent,
we can actually already start thinking
of this kind of a process that is currently
used for flexible electronics, for example.
Where we can start printing these features
and creating these sheets.
And now imagine that you can start
constructing all of your materials
by using these sheets that are really, really lightweight,
yet have the same strength as steel.
And just to wrap up in the last couple of minutes,
I wanted to show you that there are actually
multiple technological applications that we think
would benefit from this technology.
For example, in the lightweight electrodes for batteries.
You can imagine that silicon has a much larger capacity
for storing lithium, for example, than graphitic carbon
that's used today.
But it suffers from this catastrophic failure.
And what I'm showing you here is the cracked silicon.
Now, imagine these nano-trusses.
So when the silicon is taken to the nano scale,
it actually is capable of expanding by 400% or so,
which is what is needed to absorb all this lithium.
And now because it's in this truss geometry,
maybe the individual beam members
can twist out of the way, and thereby
prevent catastrophic failure.
So this would be for nano structured electrodes.
We're using these for three-dimensional cell
scaffolds.
And this is where the bone comes back into this overall playing
field, in the sense that we can now differentiate
different cells by controlling the stiffness and the roughness
of these nano-trusses.
And these are in three dimensions,
so you can start forming these artificial tissues
and maybe create artificial organs with it.
And you can see already, these are the images of the cells
that we created in our group.
You can see the different osteoblasts,
so these are bone-type cells.
And then another application we've been working on
is photovoltaics.
So these are geometries that are able to trap light in such
a way that you don't lose any light to the reflection.
And so every beam of light from the entire solar spectrum
can come into these structures and then
get trapped within these structures, and not get out.
And so, for example, we can use them
for the anti-reflective coatings.
And so these are just some of the examples
we draw our inspiration from nature.
And actually, Will here was kind enough
to lend me one of these skeletons.
You can see the whole concept of hierarchical design is not new.
What's new here is that now we can capitalize on the nano size
effect and the architecture towards creating
these bio-inspired, very tough, and very strong,
and at the same time, lightweight materials.
Thank you very much.
[APPLAUSE]