Cambridge Team Spins Nanotube Yarn

FridayBob writes "They say it's bound to happen soon, although nobody knows exactly how and when. Well, perhaps the answer has arrived. It now seems as though some bright folks at the Cambridge-MIT Institute have figured out a way to continuously spin carbon nanotubes into a fiber. Will it be strong enough for a space elevator?" They're getting closer to commercialization (see older story) but not there yet...

Comments

"Electrical current", eh?

[lfm_the_couch]

...then could we put out satellites with massive solar cells and harvest the electricity directly through the tether, rather than inventing "beamed power"? Probably not, if my dim understanding of electrical physics is any use...

Re:"Electrical current", eh?

[another_henry]

Actually, the beamed power is not tricky at all. It is easy to do using microwaves, which can be produced efficiently with magnetrons (evidence is in your microwave oven) and converted back into electricity using rectennas.

A rectenna is basically an array of tiny antennas and diodes which rectify the microwaves back to DC. They have been around since the '60s and can operate at up to 80% efficiency (record is 84% efficiency for 30kW of power).

In 1964 William C. Brown succeeded in demonstrating a microwave-powered helicopter! (Sorry, I was unable to find any pictures). You can find more interesting info on this google search.

Re:"Electrical current", eh?

[another_henry]

Stay out of the tightly-focused beam, and you'll be fine. If you don't actually catch enough to cook you there and then, it can't hurt you - radar operators used to commonly stand in front of the dishes on cold days to warm up. It's only resistive heating.

Re:"Electrical current", eh?

[silvaran]

Next, current flows on the surface of a wire.

Are you sure about that? Can you back that up with references that don't refer to:

- Superconductors (which exhibit this behavior)
- A/C skinning effect (which still doesn't flow on the surface of the wire)

As far as I knew, electric current flows through the wire, and electrons collide with one another and spin from atom to atom to reach the positive end. If current flows outside the wire in both regular wires and superconducting wires, where does the resistance come from? (I know I beg the question of whether or not current flows on the outside of a superconducting wire, but I figured this was a well-known fact).

Chain Mail

[justanyone]

Can no one see the fault in this scenario?

If you want a super-strong (tensile strength) fabric, you don't make it by crochet or other weaving methods. You make chain mail with it.

The crucial facts (IMHO) are these:

• Nanotubes have very high tensile strength (100 GPa?)
• They have very low surface friction
• they are difficult to make in long lengths
• Snags are inevitable in any real-world situation

The key here is that making a fabric like chain mail, by having nanotubes that are of a specified uniform length like 1/2 cm, formed into a continuous loop (torroid or donut shape), and interlocking these loops in a redundant chain-mail fashion (no pun intended), will lead to exceedingly strong fabric.

However, making a weave, with a long, continuous string, will lead to a fabric that can collapse by the cutting of the string at any point along it's course - this will lead to fraying and the fabric will pull apart.

Solid state physisists, please enlighten us if I'm way off base here, but it certainly seems the better way to go for high-strength tethers and fabrics.

Humbly but convincedly,

--Kevin J. Rice

Re:Chain Mail

[jgardn]

It can't happen like that. You are talking about a level of organization that only crystals exhibit.

Exactly how do you propose to make toroidal nanotubes? Exactly how are you going to interlock them into a pattern? This is the difficult part, and if you figure that out, I see a Nobel prize in your future.

Right now, the current thought in nanotube technology is that you aren't going to make a single, continuous tube. Even if you could, the maximum length is not going to be practically infinite.

Instead, what needs to happen is that you must "spin a thread", like we spin thread today. You take fibers and organize them so that they are randomly interlocking.

The difficult part is getting the nanotubes to stick together with a strength equal to the strength of the nanotubes. This is no problem with cotton, polyester, or sheep's wool, because each individual fiber is hairy and they stick together like velcro. The strength of the connection can be stronger than the strength of the individual fibers.

It is known that nanotubes are "sticky" to each other. There is a mutual attraction caused by various forces. This laboratory used that to their advantage by continuously spinning thread at the rate of several cm per second (!). However, the thread isn't sticking very well to each other or the stickiness isn't strong enough. The end result are threads that aren't much better than sewing threads.

Perhaps they can add a step where they put the nanotubes into a bath of chemicals and stretch the nanotubes or compress them to cause them to stick more strongly together. Perhaps if those threads are weaved together, the weave itself will cause the nanotubes to stick together better. Perhaps a thread can be developed that when put under tension compresses and thus increases the friction. These are all possible scenarios, and are the next steps.

Or perhaps this is just a really good way to make and store millions of nanotubes a second, to be dissolved and organized later.

Or maybe you can take these nanotubes and assemble them with some kind of process to line them up end to end. Maybe they will weld themselves chemically if they are lined up and brought near to each other's ends.

More experimentation is needed. Wouldn't you like to be in that lab at this time, playing with these threads?

Re:Chain Mail

[justanyone]

Yes, okay, it's hard to make.

But perhaps not impossible. What I'm proposing is to have the end in mind when designing the machinery.

IDEA: Perhaps fabricating nanotubes with a deliberate molecular flaw that allows attachment of another hydrophilic molecule, say, "HPM A". Then have a hydrophobic molecule B ("HPM B") similarly. Arrange for HPM-A and HPM-B to fold at a specific set of temperatures and have HPM-B disengage at that point.

In otherwords, build a molecular assembly device that manufactures a specific pattern of flat chainmail cloth, then cut it into a long strip.

Good point about the junctures being squeezed, this may cause loss of strength, but I'm not counting on it.

-- Kevin J. Rice

Larry Niven strikes again

[justanyone]

Larry Niven postulated in a Ringworld or other Known Space writing the existence of what he called 'Sinclair Molecule Chain'.

This substance was a single molecule that was very, very small in diameter, but had a very, very high tensile strength. This was formed into a string and was used in ropes and other stuff for various purposes. It was also useful for cutting things, since the chain was so strong, and the application of force across such a narrow point, that it would cut through most substances easily.

I have some questions:

• Has anyone tested this theory with this molecular chain stuff?
• Would it make a good knife?
• How vulverable is it to shocks (is it elastic or brittle)?
• Can I make a better lawnmower blade out of this stuff, much like a super-strong weedwhacker wire?
• Would chain mail (see other post) made out of it be bulletproof?
• Would it be a good instead of steel in concrete as rebar (since the main bad-thing about reinforced concrete is corrosion of the rebar)?
• Would making carbon-fiber composite structures be better with nanotubes, or would it even cut through the glue substrate?

Just some basic questions... Maybe someone from the MIT team that created this stuff can answer them.

--Kevin J. Rice

Re:Conductor

[Anonymous Coward]

If you wear a cloth conductor, the path of least resistance becomes your clothes, not your body. In some cases not a bad thing.

Toxicity of Carbon Nanotubes

[EigenHombre]

I noticed noone here has commented on the toxicity of carbon nanotubes. From the NIH website:

"These results show that, for the test conditions described here and on an equal-weight basis, if carbon nanotubes reach the lungs, they are much more toxic than carbon black and can be more toxic than quartz, which is considered a serious occupational health hazard in chronic inhalation exposures."

Not sure I'd wear a shirt or even chain mail made of these things....