Nanotech discovery could have radical implications

It has been 20 years since the futurist Eric Drexler daringly predicted a new world where miniaturized robots would build things one molecule at a time. The world of nanotechnology that Drexler envisioned is beginning to come to pass, with scientists conjuring new applications daily.

Now Salvatore Torquato, a Princeton University scientist, is proposing turning a central concept of nanotechnology on its head. If the theory bears out – and it is in its infancy -- it could have radical implications not just for industries like telecommunications and computers but also for our understanding of the nature of life.

Torquato and colleagues have published a paper in the Nov. 25 issue of Physical Review Letters, the leading physics journal, outlining a mathematical approach that would enable them to produce desired configurations of nanoparticles by manipulating the manner in which the particles interact with one another.

This may not mean much to the man on the street, but to the average scientist it is a fairly astounding proposition.

"In a sense this would allow you to play God, because the method creates, on the computer, new types of particles whose interactions are tuned precisely so as to yield a desired structure," said Pablo Debenedetti, a professor of chemical engineering at Princeton.

The standard approach in nanotechnology is to come up with new chemical structures through trial and error, by letting constituent parts react with one other as they do in nature and then seeing whether the result is useful.

Nanotechnologists rely on something called "self-assembly." Self-assembly refers to the fact that molecular building blocks do not have to be put together in some kind of miniaturized factory-like fashion. Instead, under the right conditions, they will spontaneously arrange themselves into larger, carefully organized structures.

As the researchers point out in their paper, biology offers many extraordinary examples of self-assembly, including the formation of the DNA double helix.

But Torquato and his colleagues, visiting research collaborator Frank Stillinger and physics graduate student Mikael Rechtsman, have taken an inverse approach to self-assembly.

"We stand the problem of self-assembly on its head," said Torquato, a professor of chemistry who is affiliated with the Princeton Institute for the Science and Technology of Materials, a multidisciplinary research center devoted to materials science.

Instead of employing the traditional trial-and-error method of self-assembly that is used by nanotechnologists and which is found in nature, Torquato and his colleagues start with an exact blueprint of the nanostructure they want to build.

''If one thinks of a nanomaterial as a house, our approach enables a scientist to act as architect, contractor, and day laborer all wrapped up in one," Torquato said. "We design the components of the house, such as the 2-by-4s and cement blocks, so that they will interact with each other in such a way that when you throw them together randomly they self-assemble into the desired house."

To do the same thing using current techniques, by contrast, a scientist would have to conduct endless experiments to come up with the same house. And in the end that researcher may not end up with a house at all but rather – metaphorically speaking -- with a garage or a horse stable or a grain silo.

While Torquato is a theorist rather than a practitioner, his ideas may have implications for nanostructures used in a range of applications in sensors, electronics and aerospace engineering.

"This is a wonderful example of how asking deep theoretical questions can lead to important practical applications," said Debenedetti.

So far Torquato and his colleagues have demonstrated their concept only theoretically, with computer modeling.

They illustrated their technique by considering thin films of particles. If one thinks of the particles as pennies scattered upon a table, the pennies, when laterally compressed, would normally self-assemble into a pattern called a triangular lattice.

But by optimizing the interactions of the "pennies," or particles, Torquato made them self-assemble into an entirely different pattern known as a honeycomb lattice (called that because it very much resembles a honeycomb).

Why is this important? The honeycomb lattice is the two-dimensional analog to the three-dimensional diamond lattice – the creation of which is somewhat of a holy grail in nanotechnology.

Diamonds found in nature self-assemble the way they do because the carbon atoms that are the building blocks of diamonds interact with each other in a specific way that is referred to as covalent bonding. This means that each carbon atom has to bond with exactly four neighboring atoms along specific directions.

One surprising and exciting feature of the Princeton work is that the researchers were able to achieve the honeycomb with non-directional bonding rather than covalent, or directional, bonding.

"Until now, people did not think it was possible to achieve this with non-directional interactions, so we view this as a fundamental theoretical breakthrough in statistical mechanics," Torquato said. Statistical mechanics is a field that bridges the microscopic world of individual atoms with the macroscopic world of materials that we can see and touch.

To create the honeycomb lattice, the researchers employed techniques of optimization, a field that has burgeoned since World War II and which is essentially the science of inventing mathematical methods to make things run efficiently.

Torquato and his colleagues hope that their efforts will be replicated in the laboratory using particles called colloids, which have unique properties that make them ideal candidates to test out the theory. Paul Chaikin, a professor of physics at New York University, said he is planning to do laboratory experiments based on the work.

The paper appearing in Physical Review Letters is a condensed version of a more detailed paper that has been accepted for publication in Physical Review E and which will probably appear sometime before the end of the year.

Torquato said that he and Stillinger initially had trouble attracting research money to support their idea. Colleagues "thought it was so far out in left field in terms of whether we could do what we were claiming that it was difficult to get funding for it," he said. The work was ultimately funded by the Office of Basic Energy Sciences at the U.S. Department of Energy.

"The honeycomb lattice is a simple example but it illustrates the power of our approach," Torquato said. "We envision assembling even more useful and unusual structures in the future."

I've already posted one quote from a John Ringo book series to TigerLikesRooster on this thread. As it happens there's another part of the same book that quote came from that applies to your scenario about enclosing nuclear material in Fullerene nanotubes. In his novel (Hell's Faire) Ringo introduces a UT researcher working at Oak Ridge that uses bucky-balls to microencapsulate not nuclear material but anti-matter.

It has been established (in reality) that material inserted inside a bucky-ball molecule will be suspended and not interact with the carbon or other normal matter, thus if you can manufacture antimatter and insert it within a bucky-ball without having it blow up prematurely the antimatter will be held in place safely until you "crack open" the bucky-ball.

He ends up creating a 2 megaton yield micro bomb suitable for packing into an artillery cluster round for firing from a Bull Gun.

"The system consists of fifty-five sub-projectiles with an Indowy initiator in each," Dr. Castanuelo said, pointing at the diagram on the screen. "After firing, the system reaches its target point and begins to spread projectiles. It doesn't just drop them, which would cause massive overlap, but lays them down during its flight. Each projectile has slowing fins. These have been shown to not "trip" Posleen defensive systems. This system lets all the projectiles attain complimentary altitudes. At a preprogrammed height above ground, which is determined by radar altimeters in each sub-projectile, the Indowy containment field releases a burst of anti-protons into the fullerene matrix which then sustains a rapid chain reaction."
Jack looked at the presentation as the projectiles fell out of the back of an imaginary artillery shell and scattered across a wide area. The effect looked similar to a cluster bomb until you realized that what looked like gullies and small hills in the background was a backdrop of the Rocky Mountains.
“What's the footprint?" Horner asked. He had commandeered a shuttle and flown down to the university as soon as he got the word. He still didn't know if he had the answer to a maiden's prayer or the worst nightmare since the word of the invasion.
Dr. Castanuelo cleared his throat nervously. "Thirty-five miles deep, fifteen miles across. It's the equivalent of a one hundred and ten megaton bomb, but with significantly different gross effects. For example the thermal pulse is equivalent to a two megaton."
"And you built this on your own?" Jack asked quietly. "Without authorization? Or even mentioning it? One hundred and ten megatons?"
"Well, I had the hyperfullerene and the initiators just sitting there," Dr. Castanuelo said hotly. "I thought it might come in handy."
"You thought it might come in handy. Just how much of this . . . hyperfullerene did you make?"
"Well, once we got the production model worked out it seemed reasonable to continue production," Dr. Castanuelo said defensively. "I mean, we had the power plant and the materials. After that it was easy."
"How much?" the general asked smiling faintly. The question was nearly a whisper.
"Well, as of yesterday, excepting the material in the bomb, approximately one hundred and forty kilos."
"Of hyperfullerene?" Jack asked, taking a deep breath.
"No, we generally refer to it in terms of anti-hydrogen atomic mass rather than the . . ."
"You have one hundred and forty kilos of antimatter sitting around on my planet????"
"I thought it would come in handy," the doctor said lamely.
"Sure, for fueling Ninth Fleet!" Jack shouted. "Tell me about the radioactive effects of this bomb."
"Very hot, unfortunately," the scientist sighed. "It's one of the reasons it's useless for an energy source. But very short-lived as well. In a day or two the area is down to high background and in a month it would require sophisticated sensors to tell it has been hit. But not the sort of thing you want running your car. Fortunately, it's readily detectable."
"Sure, with a Geiger counter!" President Carson said.
"Oh, no, there's a visual chemical cue," the professor said. "It was the suggestion of one of my grad students and it made sense. The truly 'hot' areas will be readily detectable visually and the cue will fade as the radiation does."
"But the entire system has not been tested," Carson pointed out with the sort of quiet calm used when an emergency happens during brain surgery.
"We fired a mockup with transmitters in duplicate Indowy containment fields," the scientist said. "They all survived. If they survived, the containment works. And hyperfullerene has been tested against every kind of shock imaginable. Unfortunately, the problem is not it detonating prematurely but getting it to detonate at all."
"And it is armed," Carson said, accusingly.
"Well, yes, that follows."
"Positive action locks?" Jack asked.
"Not yet," Castanuelo admitted. In other words, the bomb could be detonated by anyone with rudimentary technical skills.
"Guards? Electronic security? Vault safety?" the general asked furiously.
"Well, we've got it in one of our mines," the professor said with a shrug. "And I've got a couple of students watching it. Look, it was a crash project!"
Jack glanced at his wrist where his AID used to be and then at his aide. "Jackson, get on the phone. I want an outside expert in here, one on antimatter, one on Indowy containment systems and one on guns and submunitions. I want a company of regular troops around wherever this thing is in no more than an hour and I want them replaced by special operations guard units by the end of the day."
He looked at the scientist and nodded. "Dr. Castanuelo, you're right, we did need it. I'm pretty sure that that is going to keep your bacon out of the fire. As long as it works. If it doesn't . . ."
"Sir, if it doesn't, I'll never know it," Castanuelo said. "If it, for example, detonates on launch, there won't be a Knoxville left."
"And if the rest of your material sympathetically detonates, say goodbye to Tennessee!"

The "visual chemical cue" that one of his grad students suggests will "die" the country side with a bright fluorescent color that will fade as the radiation becomes safe. Being from UT they, of course, choose orange as the color to paint the dangerous countryside. They fire the round at North Georgia, where else?

The line from the book is:

"That's what you get for letting rednecks play with antimatter."

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