Tag Archives: self-assembling

Self-assembling chains of nanoparticles

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The Argonne National Laboratory (US) has announced that their researchers have for the first time watched nanoparticles assemble into chains in real-time. From the Apr. 20, 2013 news item on Nanowerk (Note: Links have been removed),

In a new study performed at the Center for Nanoscale Materials at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, researchers have for the first time seen the self-assembly of nanoparticle chains in situ, that is, in place as it occurs in real-time (“In Situ Visualization of Self-Assembly of Charged Gold Nanoparticles”).

The Apr. 19, 2013 Argonne National Laboratory press release by Jared Sagoff, which originated the news item, provides more detail,

The scientists exposed a tiny liquid “cell” or pouch that contained gold nanoparticles covered with a positively charged coating to an intense beam of electrons generated with a transmission electron microscope. Some of the electrons that penetrated the outside of the cell became trapped in the fluid medium in the cell. These “hydrated” electrons attracted the positively charged nanoparticles, which in time reduced the intensity of charge of the positive coating.

As the hydrated electrons reduced the coating’s positive charge, the nanoparticles no longer repelled each other as strongly.  Instead, their newfound relative attraction led the nanoparticles to “jump around” and eventually stick together in long chains. This self-assembly of nanoparticle chains had been detected before in different studies, but this technique allowed researchers, for the first time, to observe the phenomenon as it occurred.

“The moment-to-moment behavior of nanoparticles is something that’s not yet entirely understood by the scientific community,” said Argonne nanoscientist Yuzi Liu, the study’s lead author. “The potential of nanoparticles in all sorts of different applications and devices – from tiny machines to harvesters of new sources of energy – requires us to bring all of our resources to bear to look at how they function on the most basic physical levels.”

Self-assembly is particularly interesting to scientists because it could lead to new materials that could be used to develop new, energy-relevant technologies. “When we look at self-assembly, we’re looking to use nature as a springboard into man-made materials,” said Argonne nanoscientist Tijana Rajh, who directed the group that carried out the study.

Because the particles under study were so tiny – just a few dozen nanometers in diameter – an optical microscope would not have been able to resolve, or see, individual nanoparticles. By using the liquid cell in the transmission electron microscope at the Center for Nanoscale Materials, Liu and his colleagues could create short movies showing the quick movement of the nanoparticles as their coatings contacted the hydrated electrons.

Here’s a video of the self-assembling nanoparticles, provided by the Argonne National Laboratory,

Here’s a link to and citation for the paper,

In Situ Visualization of Self-Assembly of Charged Gold Nanoparticles by Yuzi Liu, Xiao-Min Lin, Yugang Sun, and Tijana Rajh. J. Am. Chem. Soc., [Journal of the American Chemical Socieyt] 2013, 135 (10), pp 3764–3767
DOI: 10.1021/ja312620e Publication Date (Web): February 22, 2013
Copyright © 2013 American Chemical Society

 

Virtual lego used to simulate self-assembling crystal structures

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The Jan. 17, 2013 news release on EurekAlert describes a ‘soft’ or virtual lego computer simulation developed at the University of Vienna (Austria),

In developing these novel self-assembling materials, postdoc Barbara Capone has focused on the design of organic and inorganic building blocks, which are robust and can be produced at large scale. Capone has put forward, together with her colleagues at the Universities of Vienna and Mainz, a completely new pathway for the construction of building blocks at the nanoscale.

…

The team of researchers has shown that so-called block copolymer stars – that means polymers that consist of two different blocks and they are chemically anchored on a common point – have a robust and flexible architecture and they possess the ability to self-assemble at different levels. At the single-molecule level, they first order as soft patchy colloids which serve then as “soft Lego” for the emergence of larger structures. At the next level of self-assembly, the colloids form complex crystal structures, such as diamond or cubic phases.

The spatial ordering in the crystals can be steered through the architecture of the “soft Lego” and opens up the possibility for the construction of new materials at the macroscopic scale with desired structure. In this way, crystals can be built that have applications in, e.g., photonics, acting as filters for light of certain frequencies or as light guides.

You can find illustrations of the ‘diamond’ and the ‘cube’ produced by Capone and her colleagues with the news release on EurekAlert or here at the University of Vienna’s media portal where you may be able to find more information if you can read German. Alternatively, you can read the research paper,

Telechelic Star Polymers as Self-Assembling Units from the Molecular to the Macroscopic Scale by Barbara Capone, Ivan Coluzza, Federica LoVerso, Christos N. Likos, and Ronald Blaak in Physical Review Letters 109 [issue no. 23], 238301 (2012) [5 pages]DOI:10.1103/PhysRevLett.109.238301

This article is behind a paywall.

Turning my world upside down: a new view on entropy

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Entropy as a state of increasing disorder (or everything falls apart) is a concept introduced to me during a high school chemistry class. I think the teacher was having a bad day because the concept was couched in the most depressive terms possible. However, that may the reason a very strong impression was made, so news that entropy may lead to organization definitely piqued my interest. From the July 26, 2012 news item on Nanowerk (Note: I have removed a link),

Researchers trying to herd tiny particles into useful ordered formations have found an unlikely ally: entropy, a tendency generally described as “disorder.”

Computer simulations by University of Michigan scientists and engineers show that the property can nudge particles to form organized structures. By analyzing the shapes of the particles beforehand, they can even predict what kinds of structures will form.

The findings, published in this week’s edition of Science (“Predictive Self-Assembly of Polyhedra into Complex Structures”), help lay the ground rules for making designer materials with wild capabilities such as shape-shifting skins to camouflage a vehicle or optimize its aerodynamics.

More information can be found in the University of Michigan July 26, 2012 news release by Nicole Casal Moore,

One of the major challenges is persuading the nanoparticles to create the intended structures, but recent studies by Glotzer’s [professor Sharon Glotzer] group and others showed that some simple particle shapes do so spontaneously as the particles are crowded together. The team wondered if other particle shapes could do the same.

“We studied 145 different shapes, and that gave us more data than anyone has ever had on these types of potential crystal-formers,” Glotzer SAID. “With so much information, we could begin to see just how many structures are possible from particle shape alone, and look for trends.”

Using computer code written by chemical engineering research investigator Michael Engel, applied physics graduate student Pablo Damasceno ran thousands of virtual experiments, exploring how each shape behaved under different levels of crowding. The program could handle any polyhedral shape, such as dice with any number of sides.

Left to their own devices, drifting particles find the arrangements with the highest entropy. That arrangement matches the idea that entropy is a disorder if the particles have enough space: they disperse, pointed in random directions. But crowded tightly, the particles began forming crystal structures like atoms do—even though they couldn’t make bonds. These ordered crystals had to be the high-entropy arrangements, too.

However, this isn’t a simple reversal of the  entropy concept at the nanoscale (from the Moore news release),

Glotzer explains that this isn’t really disorder creating order—entropy needs its image updated. Instead, she describes it as a measure of possibilities. If you could turn off gravity and empty a bag full of dice into a jar, the floating dice would point every which way. However, if you keep adding dice, eventually space becomes so limited that the dice have more options to align face-to-face. The same thing happens to the nanoparticles, which are so small that they feel entropy’s influence more strongly than gravity’s.

“It’s all about options. In this case, ordered arrangements produce the most possibilities, the most options. It’s counterintuitive, to be sure,” Glotzer said.

The simulation results showed that nearly 70 percent of the shapes tested produced crystal-like structures under entropy alone. But the shocker was how complicated some of these structures were, with up to 52 particles involved in the pattern that repeated throughout the crystal.

Here’s an illustration the scientists have provided,

Shapes can arrange themselves into crystal structures through entropy alone, new research from the University of Michigan shows. Image credit: P. Damasceno, M. Engel, S. Glotzer

This excerpt includes a bit more about the crystals and two of the remaining mysteries (from the Moore news release),

The particle shapes produced three crystal types: regular crystals like salt, liquid crystals as found in some flat-screen TVs and plastic crystals in which particles can spin in place. By analyzing the shape of the particle and how groups of them behave before they crystallize, Damasceno said that it is possible to predict which type of crystal the particles would make.

“The geometry of the particles themselves holds the secret for their assembly behavior,” he said.

Why the other 30 percent never formed crystal structures, remaining as disordered glasses, is a mystery.

“These may still want to form crystals but got stuck. What’s neat is that for any particle that gets stuck, we had other, awfully similar shapes forming crystals,” Glotzer said.

In addition to finding out more about how to coax nanoparticles into structures, her team will also try to discover why some shapes resist order.

Plenty of Room at the Bottom’s 50th anniversary; new advance in nanoassembly; satirizing the copyright wars; China’s social media map

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There’s plenty of room at the bottom, Richard Feynman’s December 29, 1959 talk for the American Physical Society is considered to be the starting point or origin for nanotechnology and this December marks its 50th anniversary. Chris Toumey, a cultural anthropologist at the University of South Carolina NanoCenter, has an interesting commentary about it (on Nanowerk) and he poses the question, would nanotechnology have existed without Richard Feynman’s talk? Toumey answers yes. You can read the commentary here.

In contrast to Toumey’s speculations, there’s  Colin Milburn (professor at University of California, Davis) who in his essay, Nanotechnology in the Age of Posthuman Engineering: Science Fiction as Science, suggests that nanotechnology originated in science fiction. You can read more about Milburn, find the citations for the essay I’ve mentioned, and/or download three of his other essays from here.

Ting Xu and her colleagues at the US Dept. of Energy’s Lawrence Berkeley National Laboratory have developed a new technique for self-assembling nanoparticles. From the news item on Physorg.com,

“Bring together the right basic components – nanoparticles, polymers and small molecules – stimulate the mix with a combination of heat, light or some other factors, and these components will assemble into sophisticated structures or patterns,” says Xu. “It is not dissimilar from how nature does it.”

More details are available here.

TechDirt featured a clip from This hour has 22 minutes, a satirical Canadian comedy tv programme, which pokes fun at the scaremongering which features mightily in discussions about copyright. You can find the clip here on YouTube.

I’ve been meaning to mention this tiny item from Fast Company (by Noah Robischon) about China’s social media. From the news bit,

The major players in the U.S. social media world can be counted on one hand: Facebook, MySpace, Twitter, LinkedIn. Not so in China, where the country’s 300 million online users have a panoply of popular social networks to choose from–and Facebook doesn’t even crack the top 10.

Go here to see the infographic illustrating China’s social media landscape.

Happy weekend!

Doing the impossible (superconductorwise) and self-assembling gold

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They made the electrons behave. Of course, it will be written up in much loftier terms but that’s what it comes down to. (For purists who think that you can’t end a sentence in a preposition, you are wrong. One of these days I will dig up the appropriate references.) A team at the University of British Columbia (‘UBC] yes, there is Canadian nanotechnology) have found a way to manipulate electrons on ultra thin material, in this case, potassium atoms were laid over a a piece of superconductive copper oxide. (superconductive = no resistance to conducting electricity)

As to why this is good news, here’s what the lead researcher, Dr. Andrea Damascelli has to say, “The development of future electronics, such as quantum computer chips, hinges on extremely thin layers of material.”  Sounds reasonable, so what’s the problem? He goes on, “Extremely thin layers and surfaces of superconducting material take on very different properties from the rest of the material. Electrons have been observed to rearrange, making it impossible for scientists to study.” Until recently. Damascelli adds, “The new technique opens the door to systematic studies not just of high-temperature superconductors, but many other materials where surfaces and interfaces control the physical properties.” He mentions fuel cells and lossless power lines as two potential applications. The journal, Nature Physics, is publishing Damascelli and team’s paper this week. (I imagine that you won’t be able to access the article unless you have a subscription or permission to use someone else’s subscription.) For more details you will find the press release here or at Phys.org here.

There is self-assembling gold according to Dr. Pulickel M. Ajayan at Rice University. His study will be published next month in Nano Letters. With the right conditions (exposure to magnets, chemicals, and light) Ajayan’s team coaxed nanorods into self-assembling as a giant structure (like a grain of rice). Go here for more details about the paper and an image of a giant gold droplet.