Got to thinking about nanopaper:

I wondered how much strength it would take to do this:
If you blow up a balloon with hydrogen or helium, it will rise into the air, as we all know. So what if we had a super strong paper(?) like this newly made Nanopaper, supposedly 10 times stronger than steel, made it into a sphere and then sucked all the air out of it. Would it not be just like a helium balloon but even more effective at lift?
Could such a device actually ever be built?

Originally posted by sonhouse
I wondered how much strength it would take to do this:
If you blow up a balloon with hydrogen or helium, it will rise into the air, as we all know. So what if we had a super strong paper(?) like this newly made Nanopaper, supposedly 10 times stronger than steel, made it into a sphere and then sucked all the air out of it. Would it not be just like a helium balloon but even more effective at lift?
Could such a device actually ever be built?

yes. if you sucked out "all the air" - literally - then the balloon would be lighter than if it was filled with helium. greater lift.

Yes on both counts, as said above, once the density of the entire sphere is less than a similarly sized sphere of air, it'll float.
As for constructing it, we may not be at that stage yet, but there's some great stuff being done with composite materials these days. Bucky-paper may not hold the vacuum, but a 'syntactic foam' would not leak, and though it'd be bigger, would hold a much higher pressure difference.

(The strength of nano-paper is better when it's being pulled, shear forces... like scissors, are harder for it to handle.)

Originally posted by agryson
Yes on both counts, as said above, once the density of the entire sphere is less than a similarly sized sphere of air, it'll float.
As for constructing it, we may not be at that stage yet, but there's some great stuff being done with composite materials these days. Bucky-paper may not hold the vacuum, but a 'syntactic foam' would not leak, and though it'd b ...[text shortened]... etter when it's being pulled, shear forces... like scissors, are harder for it to handle.)

Wouldn't the stresses on such a device be compressive? Like an arch bridge but all the way round in 3 dimensions?

Yes, but the slightest touch changes the system and introduces shear, you need a more rigid structure. If we can assume a perfect system though, then you're right and we could do it, though it'd need to be very perfect!

Also, nanopaper is made from fibres, (tiny, but still fibres) so the strength and toughness lie in the network, it's not a homogeneous system. That's why it would be very sensitive to slight changes. I've worked with this stuff, pulling it apart is fine, it holds well, but it's as brittle as ash if you press on it perpindicularly.

Originally posted by agryson
Yes, but the slightest touch changes the system and introduces shear, you need a more rigid structure. If we can assume a perfect system though, then you're right and we could do it, though it'd need to be very perfect!

Also, nanopaper is made from fibres, (tiny, but still fibres) so the strength and toughness lie in the network, it's not a homogeneous sy ...[text shortened]... art is fine, it holds well, but it's as brittle as ash if you press on it perpindicularly.

You actually worked with nanopaper? Carbon nanotubes 'woven' into paper?

No, not woven into paper, it was a paper made out of nothing but nanotubes. Think of how normal paper is made of woodfibres, well this stuff was paper made out of nanotubes.
I didn't actually make the stuff, I was just helping with analysis in my final year project, and there's more than one way to make nanopapers, but this particular material was really cool.

Originally posted by agryson
No, not woven into paper, it was a paper made out of nothing but nanotubes. Think of how normal paper is made of woodfibres, well this stuff was paper made out of nanotubes.
I didn't actually make the stuff, I was just helping with analysis in my final year project, and there's more than one way to make nanopapers, but this particular material was really cool.

What do they do to make it? just take a pile of bare nanotubes and run them through a roller to squash them down?

well it wasn't my project, and like I said, I didn't make them myself, but from what I was told, it's just like real paper, mix it in a solvent, drain it through a suitable mesh (porous plate). I'm sure it's a little bit more technical, but that's the basic idea.