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Published online 27 February 2008 | Nature | doi:10.1038/news.2008.629
News: Briefing
Nano makes it big
A company in the United States has made a sheet from tiny carbon nanotubes. Nature News finds out whether bigger is better when it comes to the very small.
I thought the whole point about carbon nanotubes was that they are 'nano' — really, really small.
True. As the name implies, nanotubes are on the order of 10-9 metres in size: they are famed for being thinner than human hair, and are typically less than a millimetre long.
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I'm a bit confused, here. I don't understand how it makes sense to say that it can withstand more force than stainless steel, and yet is able to be cut with scissors. And, for that matter, how it makes sense to describe it as withstanding more force than steel without it being rigid. If this is something that is purely for protecting fragile things, and it must be supported by some rigid structure underneath, then it seems to be of pretty limited use. Does it have great tensile strength, when held in place? Can we make a balloon out of it that'll hold (out) 10k atmospheres of pressure? Would this make for a good skin for an aircraft traveling at many times the speed of sound? Or is this (at least, so far) a solution in search of a problem? (I'm not trying to be facetious here (granted, I might be, but that isn't my goal), I'm just trying to figure out why this is noteworthy.)
I'm with D C on this one. I don't understand how, if it can withhold so much force, the tether "snapped" at the space elevator games. Plus how malliable is it? I mean, the picture up here looks like a bedsheet, complete with wrinkles and all. That seems pretty useless for aerospace design purposes...
Remember guys, we're talking proof of concept, R&D and first-time-ever kind of stuff here. I would imagine steel to be relatively flexible at the width the nanosheet is, so let's compare apples to apples regarding rigidity. Though the article is unspecific, I would tend to assume they are refering to tension strength, not shearing, or bending. As to protecting fragile things from physical impact without rigid structure, think bullet proof vest. Regarding the rigidity; if lateral bond strength is so high, what would a sheet one inch thick be like? Would the layers bond as strongly, or stack heterogeniously like a puff pastry that can be peeled apart? (question for the editors; Do nanotubes bond equally on all sides or only in certain configurations?) Eric; I imagine the ribbon snapped because the contest exceeded the ribbon's strength. We don't know how much it held, but I imagine it was quite high compared to standard materials. Regarding maliability, perhaps it's akin to carbon fiber, which is cloth-like until soaked in resins to form solid forms. I wish I could be on all R&D teams. It's so cool to be on the cutting edge.
D C: The seeming contradiction between being stronger than steel and yet being easily cut by scissors is because carbon nanotubes, and really any fibrous material, are what is called anisoptropic. This means that the physical properties depend upon the direction the force is applied. Carbon nanotubes are much stronger along their length than perpendicular to it, this is why a sheet of them can be cut with scissors while if one where to try and pull on then ends of the sheet to cause a similar tear it would be much more difficult. The same characteristic is present in regular paper since it is also made up of many small fibers, though it has a polymer resin added to improve its properties. I imagine that any industrial application for these nanotube sheets would also use some sort of resin since it would stop the folding and wrinkling that Eric pointed out (the folding and wrinkling is because the fiber sheets have almost no compressive strength and so deform easily when force is applied in a compressive way). Long story short nanotubes are only stronger than steel when tension is applied along their length and in order to be useful in most application they need to be stiffened with a resin, this forms a fiber composite (for example carbon fiber, kevlar, or paper)
The behavior of very thin materials is far different from their behaviours in built-up thicknesses. You can cut paper-thin stainless steel easily with a pair of household scissors, which is true of almost any metal. And aluminum foil crumples up like a bedsheet too. Same with thin fiberglass cloth. A crucial bit of info missing from the article: how thick is the sheet? Though I assume they can make it thicker by building it up more.
The responses, in particular by David Fortner, are very useful in addressing the issue of comparative strength between Nanocomp's *long* nanotube sheets and common metals. Use of our materials as part of a composite solution, along with resin treatments and other post-processing techniques, is where their true mechanical properties can be maximized. As for thickness, our materials range up to 100 microns, depending on the time duration of our production runs. Lastly, just for clarification, our space elevator tether submission broke at a knot as opposed to the fiber itself.
This seems to be a bit premature. Yes they manufactured a nanotube fabric, but its held together with 'electrostatic forces'. If the manufacturing technology existed to create nanotubes longer than 'a few milimiters' and we used those essentially as fibres in a more traditional means the breaking strength would be several orders of magnitude stronger. This is an area of heavy research. I also wonder about the cost per sq. inch.
Just a question. Could you create a cloaking device using nanotube technology?
R K: You are right that longer would be better but I think you are underestimating the "electrostatic forces" a little. Electrostatic forces act essentially like friction at the nanoscale and since the nanotubes are so small, so long, and so numerous throughout the sheet there is an enormous amount of surface area over which the electrostatic forces can act. Also take into account that electrostatic forces get exponentially more powerful the less distance is between the two surfaces interfacing and I imagine that the attractive forces between the nanotubes are quite strong and the sheets are strong enough to be useful in modern applications as they are (In applications where resin is added the resin acts to distribute forces across the entire sheet, supplementing the electrostatic forces and making the composite even stronger). The fact that they will become better and better as length of the individual nanotubes increases does not mean that Nanocomp should wait before producing what they have, since it is already a marketable product. I wonder about the cost per sq. inch also.
Mihi: I've seen articles about using carbon nanotubes to absorb light in order to make radar invisible materials and others about using materials (I think some were nanotubes, just not carbon) with suitable optical properties to cause light to somehow wrap around an object, though none that I have seen work with light in the visible spectrum. I suggest you google "nanotube invisibility cloak" or something. Wow I've been commenting a lot on this article...
I am confused about this report, in this report, it was said that the CNTs were connected though electrostatic force, I think that might be pi-pi stacking. in this sense , the complex connected through this weak interaction could not own these super properties such as high strength. the properties which were cited in the reported were the properties of CNT, not sheets formed of CNT. then I can believe the CNTs could not be aligned in such a form industrial.
Well, interesting enough.I am wondering about the fact that, it can have the strength up to 1000 MPa.If it is possible then what what can be its possible application where frictions matters a lot, I mean it has the property of good heat onductance.In that case the heat generated from friction may cause the structural deformation, isn't it? And another question.What about the polymeric material, like Kevler that has an extraordinary strength.Can this nanocomp be a replacement of the existing super hard material? If so, then what may be the possible time period to come into practical application as well as price?