By building a structure out of DNA and then coating it with glass, a research team led by Oleg Gang has created a very strong material with very low density.Gang and colleagues report that by building a structure out of DNA and then coating it with glass, they have created a very strong material with very low density. Glass might seem a surprising choice, as it shatters easily. However, glass usually shatters because of a flaw–such as a crack, scratch, or missing atoms–in its structure. A flawless cubic centimeter of glass can withstand 10 tons of pressure, more than three times the pressure that imploded the Oceangate Titan submersible near the Titanic this summer.
It’s very difficult to create a large piece of glass without flaws. But the researchers knew how to make very small flawless pieces. As long as glass is less than a micrometer thick, it’s almost always flawless. And since the density of glass is much lower than metals and ceramics, any structures made of flawless nano-sized glass should be strong and lightweight.
The glass only just coated the strands of DNA, leaving a large part of the material volume as empty space, much like the rooms within a house or building. The DNA skeleton reinforced the thin, flawless coating of glass making the material very strong, and the voids comprising most of the material’s volume made it lightweight. As a result, glass nanolattice structures are four times higher in strength but five times lower in density than steel. This unusual combination of lightweight and high strength has never been achieved before.
Materials that are both strong and lightweight could improve everything from cars to body armor. But usually, the two qualities are mutually exclusive. Now, researchers from Columbia Engineering, University of Connecticut (UConn), and Brookhaven National Lab (BNL) have developed an extraordinarily strong, lightweight material using two unlikely building blocks: DNA and glass.
“An ability to structure materials into prescribed architectures at nanoscale was envisioned as a way to enhance its mechanical properties, but there is no easy way to build at such small scales. Our DNA-based self-assembly strategy now demonstrates that it is possible,” says Oleg Gang, professor of chemical engineering and of applied physics and materials science at Columbia Engineering and a scientist at BNL who directed the work published July 19 in Cell Reports Physical Science.
Highlights
• Fabrication of 3D silica nanostructures via DNA assembly and templating
• In situ micro-compression testing to examine the mechanical properties
• Nanostructures show a nearly theoretical compressive strength of 5 GPa
Summary
Continuous nanolattices are an emerging class of mechanical metamaterials that are highly attractive due to their superior strength-to-weight ratios, which originate from their spatial architectures and nanoscale-sized elements possessing near-theoretical strength. Rational design of frameworks remains challenging below 50 nm because of limited methods to arrange small elements into complex architectures. Here, we fabricate silica frameworks with ∼4- to 20-nm-thick elements using self-assembly and silica templating of DNA origami nanolattices and perform in situ micro-compression testing to examine the mechanical properties. We observe strong effects of lattice dimensions on yield strength and failure mode. Silica nanolattices are found to exhibit yield strengths higher than those of any known engineering materials with similar mass density. The robust coordination of the nanothin and strong silica elements leads to the combination of lightweight and high-strength framework materials offering an effective strategy for the fabrication of nanoarchitected materials with superior mechanical properties.
“For the given density, our material is the strongest known,” says Seok-Woo Lee, a materials scientist at UConn who co-directed the study.
Strength is relative. Iron, for example, can take seven tons of pressure per square centimeter. But it’s also very dense and heavy, weighing 7.8 grams/cubic centimeter. Other metals, such as titanium, are stronger and lighter than iron. And certain alloys combining multiple elements are even stronger. Strong, lightweight materials have allowed for lightweight body armor, better medical devices, and made safer, faster cars and airplanes. The easiest way to extend the range of an electric vehicle, for example, is not to enlarge the battery but rather make the vehicle itself lighter without sacrificing safety and lifetime. But traditional metallurgical techniques have reached a limit in recent years, and materials scientists have had to get even more creative to develop new lightweight high-strength materials.
Materials scientists from Columbia Engineering, UConn, and BNL built an exceptionally strong, lightweight material out of DNA scaffold that allowed the formation of nanostructured silica, a glass-like material. The series of images at the top (A) shows how the skeleton of the structure is assembled with DNA, then coated with glass. (B) shows a transmission electron microscope image of the material, and (C) shows a scanning electron microscope image of it, with the two right-hand panels zooming in to features at different scales.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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Yet another cubic octet truss scaffold material for assembly/coating. Nice to have some choices though.
High compressive strength is good, but it’s not the same as high tensile strength (stretching), and not the same as plasticity (bending and deformation) or toughness (resisting impacts).
My guess is this material would have moderate to low tensile strength, moderate to low toughness, and low plasticity (it would be brittle). This is essentially a ceramic foam. So applications would be limited accordingly. No car bodies, probably.
I had the same thought. And I wondered what the properties would be for a carbon fiber composite, where this material replaced the resin. Such as a block of this material with carbon nanotubes embedded in it, aligned in the direction where you wanted tensile strength.
That might give both tensile and compressive strength at the same time.
Though it would probably still be terrible for plasticity. And maybe terrible for toughness.
The trouble with carbon nanotubes is that they’re difficult to make in bulk, and are therefore expensive. (I expect the same is true for this material, since it’s based on a DNA scaffold). If you could make carbon nanotubes in bulk, you wouldn’t need this material. A bulk sample of carbon nanotubes will likely have pretty decent compressive strength (that may be an understatement), and we already know they have excellent tensile strength.
As for regular carbon fiber, yea, what gives CFRP its relative toughness is the matrix. The fibers are pretty brittle.
Still though, if they graphitized the DNA scaffold, that might be an interesting start.
Interesting. I haven’t heard before the claim that carbon nanotubes have compressive strength. I thought they were very flexible, so they would only have tensile strength. Is there a link to evidence suggesting compressive strength?
Just my own prediction. I haven’t seen any data on this.
Obviously, if you take a narrow bundle of nanotubes, like a fiber, and try to compress it along its axis, it will buckle. But if you take a thick brick of nothing but nanotubes, the buckling mode is restricted, since they will press against each other.
With the buckling mode blocked, I don’t think you can compress a nanotube along its axis all that much. The atoms there are right on top of each other, and the bonds are pretty strong. Diamonds gets their strength form single bonds. Here you have all delocalized double bonds. IF you apply enough force, the bonds will eventually break, but it will probably take a lot.
Likewise if you try to compress it perpendicular to its axis. It may flatten a little, but the bonds are already strained, and they’re pretty strong. With enough force the bonds could break and the tube would rupture, but it would probably take a lot (but I think less than along the axis). You’re more likely to get the tubes sliding past each other well before they start rupturing.
Multi-walled nanotubes should be even harder to compress, in either axis.
(Btw, if it’s only a local rupture, and all the atoms are still in place, it could probably self-heal once the load is removed. Because the rest of the tube would still hold everything in place, and you’d just have a bunch of dangling bonds waiting to reconnect.)
Which leaves primarily shear failure modes for a thick bulk sample. But if you have a tangled mess of very long nanotubes, similar to a regular polymer, then the shear modes are also limited by tangling. Plus you could functionalize and cross-link them to improve the shear strength.
As the old saying goes, you can pull an object with a string, but you can’t push a string. Carbon nanotubes are like extremely flexible strings. And they aren’t very sticky to each other.
For ordinary strings or twine, You could put many parallel strings together to form large, solid cylinder. Applying compression along their axis will cause them to all buckle, and the cylinder as a whole will easily deform.
It’s even worse if you lay the cylinder horizontally on a table and apply compressive force orthogonal to their orientation. They will slip right past each other, and your cylinder will deform into a flat blob. For a large bundle, you don’t even need to press on it; gravity alone will deform it a great deal.
I would expect a bundle of carbon nanotubes to act similarly. A carbon nanotube may be stiff over a distance of a nanometer, but is extremely flexible over a distance of millimeters. And they aren’t going to be very sticky. They will easily slide over each other.
The question is, can you reduce the buckling and shear failure modes, and by how much. It may not be trivial, but it’s an engineering problem. Shear by sliding is also a problem for tensile applications, so it will need to be solved for large-scale applications anyway.
The simplest thing you could do (conceptually) is try to get them to tangle as much as possible.
Or you can take a tight bundle of nanotubes, and wrap the bundle with another nanotune (or several, in alternating directions). The wrapped tubes won’t have room to buckle, since they’re held together by the wrapping. They can only buckle together as a fiber. Now, take a bundle of these small wrapped fibers, and wrap that in the same type of fiber. Repeat on multiple scales, until you get thick beams. Wrap those too, if you want.
On a chemical level, one can functionalize the nanotubes with hydrogen bonding groups. Or, if you mix carbon nanotubes with fullerenes with a bit of water vapor or carbon dioxide, they react to form nanobuds. That alone should make it harder for the tubes to slide past each other. But if the tubes are tightly packed, and the vapor is still present, there’s nothing stopping the buds from reacting at their other end with an adjacent tube. So you should get nanotube-like cross-links.
wikipedia /wiki/Carbon_nanobud
Finally, if we’re talking about a nanolattice of bonded tubes, like a nano truss of carbon nanotubes, then there isn’t going to be millimeters of free nanotubes in there (or even microns, if the lattice is small enough).
We know from the carbon fiber example, that at the very least, if you bond them with a resin, you can make strong and stiff parts that stand up to compressive loads as well.
Right now, the best we can do with CNTs is disperse a small amount of them in the resin. But if we could make more of them, then we could do 60% and 80% loading, like we do with carbon fiber. The resin would hold them in place, and most of the strength would come from the tubes.
Then there’s all the other modifications I proposed above.
PS: On the molecular level, polyethylene is a bunch of very flexible strings too, much more flexible than CNTs. No hydrogen bonding, no branching, just flexible linear chains with nothing but Van-der-Waals forces between them. And yet, we can still make solid objects from it just fine.
AFAIK separating CNTs is actually a major technical challenge. They do tend to clump naturally.
Btw, “very flexible” is a somewhat relative concept. They’re actually one of the stiffest materials known. It’s just that their aspect ratio is also very high, usually. So they can still bend over a long enough scale, but their bending radius would be much larger than something like polyethyele, for example.
Very promising, bigger wind turbine blades, lighter rockets, medical devices and sports equipment. When do we get our space elevator?
Roald Dahl approves this post 🙂