Lecture 1: The Spider that Spun a Suspension Bridge

Everything about a spider's web - from the material it is spun from, to the glue that binds it together - is an engineering masterpiece. Built in seconds, each strand in the web is a highly engineered polymer fibre, 10-times stronger than steel. Like spiders, we use a wide range of polymer fibres to build the world around us. This lecture explores how chemistry is trying to mimic the natural world and construct a more ambitious and efficient man-made one.

Professor Tony Ryan
[Tony abseils from roof.] Have you ever stopped and looked around and wondered where all the material that you use comes from, and how it is made?

In this series of lectures we're going to look at how human beings, when they're faced with a problem, get back to the basics, the chemistry and the physics of the world that's around them and the materials that they use and that's why we've become the dominant species on the planet.

Professor Tony Ryan
So, that was exciting.
[Tony stands by desk.] But what was holding me up?
A rope, a rope made from chemicals that are very similar to those that are coming out of my friend Sheena's backside.
[Shot of spider & web.] Her web and my rope are made of long chain molecules known as polymers and these are the real stars of the lecture.

Professor Tony Ryan
They're all around us.
They keep us warm in the form of clothing - we eat them and in fact inside every cell in your body is a little bundle of a polymer that contains the information to make you and it's called DNA.
So polymers are made by joining lots of small molecules together.

Sometimes this looks like magic!
So here I have a collection of monomers. And I'm going to pour them into my reactor, it could be a factory, it could be a spider.

But they don't join together to make a polymer until I do something special.
And my friend Fritz here is the expert.
[Fritz & Tony stand in front of desk.] So Fritz, you come round this side, I'll go this side and he brought the spiders, so he's the 'Spiderman!'

Now, what we're going to do is we're going to pour the monomers into the reactor and there they all go and they've not made a polymer yet.
We need to do something special - we have to add a catalyst.
So Fritz please, put the copper catalyst in.
[Fritz drops catalyst into container.] We gave the box a shake and here we have a polymer chain comes flying out, not all of the monomers get joined up.
You have to keep it shaking to keep the reaction going and all the monomers have gone.

We've made a beautiful polymer chain.
Thank you very much, Fritz.

Applause

Professor Tony Ryan
[Shot of spider.] So the spider that's sat here making polymer that we're winding up is taking a fluid from her body and squeezing it out to transform it into a solid and Bipin and I are going to do an experiment that looks just like that.

[Shot of oil/water container.] We're making a polymer that's quite similar.
So he's taking a liquid, in this case, an oil and that has little molecules in, called monomers.
And then he's putting another liquid on the top, in this case it's water and that has a different monomer in.
And at the interface we get a polymer formed.
So just to show you what's happening, we went to St. Wilfred's School and made some children play the parts of the molecules.

So here they are. [Tony looks up at screen showing children acting out molecule parts.]
The blue ones at the top are running round, just like the molecules in the solution and the yellow ones at the bottom are doing the same, but when they meet at the interface, they join up, yellow/blue, yellow/blue, yellow/blue and make a polymer.
[Tony pulls thread from liquid in container.] So Bipin's going to pull a polymer out from the interface, I'm going to try and catch it - which I have.
Thank you very much - and we're going to raise it gently ... some big bits in there, looks like a shark's laid an egg halfway up my polymer chain and right from the interface, look here, we can see a polymer being formed and those molecules are joining up as it's reaching all the way to the top of the ceiling.[Shot of thread stretching up to roof of lecture theatre.]

We're going to get about 10 metres of nylon out of those solutions.
So this polymer has its crystal structure displayed on the screen and I'll explain to you where that crystal structure came from later.

Wow, and thank you - that great video piece was recorded at St. Wilfred's school and here are some of the children who took part. Thank you very much indeed. [Shot of St. Wilfred's children in audience.][Applause]

Give us a wave![Shot of kids waving.]

[Shot of Sheena the spider on table.] Now Sheena here is making silk and that silk's slightly different to the nylon.
It's made from the same elements - carbon, hydrogen, nitrogen, oxygen.
But they're put together in a slightly different way and that means that their properties are different, so I want some volunteers to help me test mechanical properties.
We'll take this boy here from the front and the young lady in the black 't' shirt and the glasses and the boy sat behind her in the yellow.
If you three would come down and join me.

[Tony shakes hands with children.] What's your name? [Charlie] - Charlie - [yes] - pleased to meet you, Charlie. And what's your name? Jessica? And John.

Right, me and Charlie are going to test the mechanical properties of this soft stuff, it's called rubber.
Now I need you to hold on, you might need to hold on with both hands. [Tony & Charlie hold ends of rubber strip.]

Professor Tony Ryan
We don't have to pull hard, because it's really easy to stretch.
Now don't let go, because it snaps back, OK, because it's a big elastic band.

But you can see how flexible it is.
Thank you very much.
Just wait there for a moment.

[Tony & Jessica hold ends of material.] And we're going to look at this material - Jessica.
Polyethylene, let's pull, slowly, pull slowly, slowly, oh!
Right, that wouldn't have been very good to come down from the ceiling on, would it?
Thank you very much.

And what about this material? This is more like my rope.

[Tony & John pull at each end of rope.] It's flexible, like the rubber, but when we pull - it doesn't stretch at all - right.

And it's because the properties are very different. Thank you all very much.

[Downshot of lecture theatre & audience.] Applause

Professor Tony Ryan
But we couldn't rely on those pulling tests and describing the properties if we're going to manufacture something that we can use safely - especially for someone as big as me to come down from the ceiling. We need to know exactly what the materials are and we use one of these instruments to accurately measure the mechanical properties.
[Shot of machine.] So we have - Anna here has loaded up some nylon and some silk into this Instron machine and we're going to start pulling them apart and down here you'll be able to read what the properties are. [Anna & Tony stand at either side.]

[Shot of graph on screen.] So if we start the test - so we're starting to stretch and this graph shows you what the force is and it goes up and up - and up - and up .... off screen and then eventually one of the polymers is going to start to break.
Right, you see the nylon fibres are popping, one by one, and the force is coming down and the silk is still going strong.

Now if I hadn't told you what the result was, what would you have expected?

Right, you'd always think that nylon's going to be stronger than spider silk, wouldn't you. Yeah? I mean I would have, if I hadn't done the test an hour ago. [Laughter]

Professor Tony Ryan
Right, and what's that difference?

Well, in the nylon you saw that the molecules were all stretched out and in the silk they're all tangled up and I want to use all your hands to do a demo. So all get your hands out please, wave them in the air, so I can see them, right.

[Audience shots intercut with shots of Tony/hands together.] And I want you to put them together, just with your fingers, like this. And this is like the polymer chains that are lined up next to each other. And I want you to pull and look, your hands pop apart, don't they? You can just slide them past each other.

But if you interlock them like this, these are like the tangles in the nylon.
And these are also like the tangles in the silk and when you pull them past each other they don't go, do they?
And the spider engineers more of those tangles into her silk than we can engineer into the nylon.

So let's say I wanted to run down from the ceiling on some of this web. Would I be able to do it?
No, because there's only individual threads.
[Rope-making machine model is brought in.] If I want to make a rope, I need to put more and more material together, so with one thread we'll hold one gram and I need to hold a hundred kilograms - I need all of those threads to be together and the way we do that is to make the fibres effectively fatter by making a rope.
[Oliver & David take up places.] So Oliver and David who are up here - have already been in to learn how to make rope.

So if we take up our positions, boys, thank you very much for coming down. And I am going to get in the middle.

Now you remember what to do with the turning? [Yep]. Yep.

[Shot of spider.] So this is really complicated, isn't it, compared to what old Sheena has to do. Are we ready?

[Shot showing rope plait being made.] So I can see that there are some girls in the audience with long hair. You've made plaits, right - and that's exactly what's happening here. The plait is being made with all this rope and these things are called rope walks for this very reason, that Annie's walking along the rope.

Thank you very much indeed, well done. Applause