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Hierarchical Design

Strong and stiff and materials comprised of mostly air are well on their way to commercialization. In this World Economic Forum Discussion, Caltech materials scientist Julia Greer talks about their use in "hierarchal design," and the impact it will have on increased efficiency and the prominence of solar cells.

Released on 01/17/2014

Transcript

(atmospheric music)

We're shifting the paradigm of materials creation,

towards something that's driven by the end goal.

So instead of saying,

these are all the processes that are available to us,

and so the material that we can expect

would have these kinds of properties,

we're doing it backwards.

I want the material to have a certain strength,

a certain weight,

and based on that we would like to predict

what kind of architecture, what kind of structure

this material is going to have.

What we have been doing in our lab is precisely that.

We are creating materials that are very, very lightweight,

that can be up to 99% air.

But yet that retain their very high stiffness,

or high strength of their parent material.

The concept that we are taking advantage of here

is very similar to that of the hard, biological systems.

It's called a Hierarchical Design.

So the concept of the Hierarchical Design,

may be analogous to comparing the Great Pyramid of Giza

and the Eiffel Tower.

The pyramid stands 174 meters tall,

and it weighs 10 megatons.

Now if you compare it to the Eiffel Tower

it's 374 meters tall,

and it weighs only

5.7 kilotons.

So, there's a difference in a factor of a thousand,

between their weight, yet the Eiffel Tower is

very, very strong and it's very, very tall.

So, what happened was that there were elements of

architecture introduced into the design

of a pyramid effectively,

that allowed it to be stronger and more lightweight,

and hence use a lot less of the material,

constituent materials, and be a lot cheaper to construct.

If we really want to reduce our reliance on fossil fuels,

we really need to figure out a way to make materials

be lighter, but yet retain all the other lucrative

structural properties.

For example, strength and stiffness.

There's a huge race right now to who can make the

most efficient solar cells, and they're still not

anywhere near the theoretical limit.

Imagine if you could take a variety of different modules,

solar cell modules that are very small.

So macroscopically it will appear like a flat sheet.

And so it will be a solar panel,

just like we would expect.

But microscopically, it will actually be

a huge array of individual solar cells.

And what that will enable is a much cheaper

production of the solar cells,

so that solar actually has a chance

to compete with the fossil fuels

and be utilized as an alternative,

viable energy source.

The major obstacle to these materials being inserted

into viable technological applications today

is the lack of any kind of a manufactural process.

So we can't mass-produce them.

If there was a way for the universities

and the companies,

and also the policy-makers to all

work together and form these partnerships,

it would be very powerful,

and we could really start inserting these

into the real world applications.

Starring: Julia Greer

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