Tag Archives: self-assembling

Nanoscale snowman and Season’s Greetings

It’s being described as a ‘jeweled nano-snowman’ but platinum and titanium aren’t my idea of jewels. Still, it’s a cheerful, seasonal greeting.

Courtesy of the University of Birmingham Nanoscale Physics Research Laboratory

Courtesy of the University of Birmingham Nanoscale Physics Research Laboratory

A December 22, 2015 news item on Nanowerk tells more of the story,

Would a jewel-encrusted snowman make the perfect Christmas present? At only 5 nanometres in size, the price might be lower than you think. And it’s functional too, catalysing the splitting of water to make green hydrogen for fuel cells.

A December 22, 2015 University of Birmingham Nanoscale Physics Research Laboratory (NPRL) press release, which originated the news item, provides more detail,

The nanoparticle, as imaged with an aberration-corrected scanning transmission electron microscope, features eyes, nose and mouth of precious-metal platinum clusters embedded in a titanium dioxide face. Each platinum cluster typically contains 30 platinum atoms; within the whole nanoparticle there are approximately 1,680 titanium atoms and 180 platinum atoms. The nano-snowman formed spontaneously from a self-assembled platinum-titanium nanoparticle which was oxidised in air, drawing the titanium atoms out to the surface. The self-assembly occurred in a gas phase, cluster beam condensation source, before size-selection with a mass spectrometer and deposition onto a carbon surface for oxidation and then imaging. The mass of the snowman is 120,000 atomic mass units. Compared with a more conventional pure platinum catalyst particle, the inclusion of the titanium atoms offers two potential benefits: dilution of how much precious platinum is needed to perform the catalysis, and protection of the platinum cores against sintering (i.e. aggregation of the nanoparticles). The shell is porous enough to allow hydrogen through and the particles are functional in the hydrogen evolution reaction. The research was performed at the Nanoscale Physics Research Lab by Caroline Blackmore and Ross Griffin. …

The scientists did a little bit of work adding colour (most of these images are gray on gray), as well as, the holly and berry frame.

Joyeux Noël et Bonne Année or Season’s Greetings!

Self-assembling copper and physiology

An Aug. 24, 2015 news item on Nanowerk highlights work at Louisiana Tech University (US) on self-assembling copper nanocomposites in liquid form,

Faculty at Louisiana Tech University have discovered, for the first time, a new nanocomposite formed by the self-assembly of copper and a biological component that occurs under physiological conditions, which are similar those found in the human body and could be used in targeted drug delivery for fighting diseases such as cancer.

The team, led by Dr. Mark DeCoster, the James E. Wyche III Endowed Associate Professor in Biomedical Engineering at Louisiana Tech, has also discovered a way for this synthesis to be carried out in liquid form. This would allow for controlling the scale of the synthesis up or down, and to grow structures with larger features, so they can be observed.

An Aug. 24, 2015 Louisiana Tech University news release by Dave Guerin, which originated the news item, describes possible future  applications and the lead researcher’s startup company,

“We are currently investigating how this new material interacts with cells,” said DeCoster. “It may be used, for example for drug delivery, which could be used in theory for fighting diseases such as cancer. Also, as a result of the copper component that we used, there could be some interesting electronics, energy, or optics applications that could impact consumer products. In addition, copper has some interesting and useful antimicrobial features.

“Finally, as the recent environmental spill of mining waste into river systems showed us, metals, including copper, can sometimes make their way into freshwater systems, so our newly discovered metal-composite methods could provide a way to “bind up” unwanted copper into a useful or more stable form.”

DeCoster said there were two aspects of this discovery that surprised him and his research team. First, they found that once formed, these copper nanocomposites were incredibly stable both in liquid or dried form, and remained stable for years. “We have been carrying out this research for at least four years and have a number of samples that are at least two years old and still stable,” DeCoster said.

Second, DeCoster’s group was very surprised that these composites are resistant to agglomeration, which is the process by which material clumps or sticks together.

“This is of benefit because it allows us to work with individual structures in order to separate or modify them chemically,” explains DeCoster. “When materials stick together and clump, as many do, it is much harder to work with them in a logical way. Both of these aspects, however, fit with our hypothesis that the self-assembly that we have discovered is putting positively charged copper together with negatively charged sulfur-containing cystine.”

The research discovery was a team effort that included DeCoster and Louisiana Tech students at the bachelor, master and doctoral level. “The quality of my team in putting together a sustained effort to figure out what was needed to reproducibly carry out the new self-assembly methods and to simplify them really speaks well as to what can be accomplished at Louisiana Tech University,” DeCoster said. “Furthermore, the work is very multi-disciplinary, meaning that it required nanotechnology as well as biological and biochemical insights to make it all work, as well as some essential core instrumentation that we have at Louisiana Tech.”

DeCoster says the future of this research has some potentially high impacts. He and his team are speaking with colleagues and collaborators about how to test these new nanocomposites for applications in bioengineering and larger composites such as materials that would be large enough to be hand-held.

“Our recent publication of the work could generate some interest and new ideas,” said DeCoster. “We are working on new proposals to fund the research and to keep it moving forward. We are currently making these materials on an ‘as needed’ basis, knowing that they can be stored once generated, and if we discover new uses for the nanocomposites, then applications for the materials could lead to income generation through a start-up company that I have formed.”

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

MediumGeneration of Scalable, Metallic High-Aspect Ratio Nanocomposites in a Biological Liquid Medium by Kinsey Cotton Kelly, Jessica R. Wasserman, Sneha Deodhar, Justin Huckaby, and Mark A. DeCoster. J. Vis. Exp. [Journal of Visual Experimentation; JoVE] (101), e52901, doi:10.3791/52901 (2015).

This paper/video is behind a paywall.

There’s more than one black gold

‘Black gold’ is a phrase I associate with oil, signifying its importance and desirability. These days, this analogic phrase can describe a material according to a July 24, 2015 news item on Nanowerk,

If colloidal gold [gold in solution] self-assembles into the form of larger vesicles, a three-dimensional state can be achieved that is called “black gold” because it absorbs almost the entire spectrum of visible light. How this novel intense plasmonic state can be established and what its characteristics and potential medical applications are is explored by Chinese scientists and reported in the journal Angewandte Chemie …

A July 24, 2015 Wiley (Angewandte Chemie) press release, which originated the news item, provides more details,

Metal nanostructures can self-assemble into superstructures that offer intriguing new spectroscopic and mechanical properties. Plasmonic coupling plays a particular role in this context. For example, it has been found that plasmonic metal nanoparticles help to scatter the incoming light across the surface of the Si substrate at resonance wavelengths, therefore enhancing the light absorbing potential and thus the effectivity of solar cells.

On the other hand, plasmonic vesicles are the promising theranostic platform for biomedical applications, a notion which inspired Yue Li and Cuncheng Li of the Chinese Academy of Science, Hefei, China, and the University of Jinan, China, as well as collaborators to prepare plasmonic colloidosomes composed of gold nanospheres.

As the method of choice, the scientists have designed an emulsion-templating approach based on monodispersed gold nanospheres as building blocks, which arranged themselves into large spherical vesicles in a reverse emulsion system.

The resulting plasmonic vesicles were of micrometer-size and had a shell composed of hexagonally close-packed colloidal nanosphere particles in bilayer or, for the very large superspheres, multilayer arrangement, which provided the enhanced stability.

“A key advantage of this system is that such self-assembly can avoid the introduction of complex stabilization processes to lock the nanoparticles together”, the authors explain.

The hollow spheres exhibited an intense plasmonic resonance in their three-dimensionally packed structure and had a dark black appearance compared to the brick red color of the original gold nanoparticles. The “black gold” was thus characterized by a strong broadband absorption in the visible light and a very regular vesicle superstructure. In medicine, gold vesicles are intensively discussed as vehicles for the drug delivery to tumor cells, and, therefore, it could be envisaged to exploit the specific light-matter interaction of such plasmonic vesicle structures for medical use, but many other applications are also feasible, as the authors propose: “The presented strategy will pave a way to achieve noble-metal superstructures for biosensors, drug delivery, photothermal therapy, optical microcavity, and microreaction platforms.” This will prove the flexibility and versatility of the noble-metal nanostructures.

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

Black Gold: Plasmonic Colloidosomes with Broadband Absorption Self-Assembled from Monodispersed Gold Nanospheres by Using a Reverse Emulsion System by Dilong Liu, Dr. Fei Zhou, Cuncheng Li, Tao Zhang, Honghua Zhang, Prof. Weiping Cai, and Prof. Yue Li. Angewandte Chemie International Edition Article first published online: 25 JUN 2015 DOI: 10.1002/anie.201503384

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

There is an image illustrating the work but, sadly, the gold doesn’t look black,


© Wiley-VCH

That’s it!

Self-assembling nanofibres could help mitigate side effects from pain killers

The research itself is pretty exciting but even more so is the fact that it was conducted by an undergraduate student. From an April 3, 2015 news item on Azonano,

A Chemistry undergraduate at the University of York [UK] has helped to develop a new drug release gel, which may help avoid some of the side effects of painkillers such as ibuprofen and naproxen.

In a final year project, MChem undergraduate student Edward Howe, working in Professor David Smith’s research team in the Department of Chemistry at York looked for a way of eliminating the adverse side-effects associated pain-killing drugs, particularly in the stomach, and the problems, such as ulceration, this could cause patients.

A March 31, 2015 University of York press release, which originated the news item, describes the research in more detail,

Supervised by PhD student Babatunde Okesola, whose research is supported by The Wild Chemistry Scholars Fund, Edward hoped to create gels which could interact with drugs such as Naproxen, and release them at the slightly alkaline pH values found in the intestine rather than the acidic conditions in the stomach.  His aim was to both protect the pain-killing drugs and help limit some of the side effects they can cause.

The researchers created a new gel, based on small molecules which self-assemble into nanofibers which could interact with a variety of anti-inflammatory, painkiller drugs, including iburofen and naproxen. The research is published in Chemical Communications.

Specific interactions between the gel nanofibres and the drugs meant that high loadings could be achieved, and more importantly, the release of the drug could be precisely controlled.  The gels were able to release naproxen at pH 8 – the value found in the intestine, but not at lower pH values found elsewhere in the body.

Professor Smith said: “Although researchers have used gels before to try and improve the formulation of naproxen, this is the first time that a self-assembling system has been used for the job, with the advantages of directed interactions between the nanoscale delivery scaffold and the drug.  As such, this is the first time that such precise control has been achieved.”

Edward Howe said: “The research really fascinated me. The prospect of being involved in developing a method to reduce the pain of others filled me with great pride. Understanding the interactions between the gel and the painkillers was very interesting and improved my knowledge of supramolecular chemistry.”

The next step for Professor Smith’s team will involve stabilising the gel drug delivery systems in the very acidic, low pH conditions found in the stomach so that they can transit safely to the intestine before delivering naproxen just where it is needed.

Professor Smith added: “Perhaps this is something that one of next year’s undergraduate project students might solve. As a research-intensive institution, York is committed to its undergraduates carrying out cutting-edge research such as this.”

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

Self-assembled sorbitol-derived supramolecular hydrogels for the controlled encapsulation and release of active pharmaceutical ingredients by Edward J. Howe, Babatunde O. Okesola, and David K. Smith. Chem. Commun., 2015, Advance Article DOI: 10.1039/C5CC01868D First published online 31 Mar 2015

This paper is behind a paywall.

Self-organizing nanotubes and nonequilibrium systems provide insights into evolution and artificial life

If you’re interested in the second law of thermodynamics, this Feb. 10, 2015 news item on ScienceDaily provides some insight into the second law, self-organized systems, and evolution,

The second law of thermodynamics tells us that all systems evolve toward a state of maximum entropy, wherein all energy is dissipated as heat, and no available energy remains to do work. Since the mid-20th century, research has pointed to an extension of the second law for nonequilibrium systems: the Maximum Entropy Production Principle (MEPP) states that a system away from equilibrium evolves in such a way as to maximize entropy production, given present constraints.

Now, physicists Alexey Bezryadin, Alfred Hubler, and Andrey Belkin from the University of Illinois at Urbana-Champaign, have demonstrated the emergence of self-organized structures that drive the evolution of a non-equilibrium system to a state of maximum entropy production. The authors suggest MEPP underlies the evolution of the artificial system’s self-organization, in the same way that it underlies the evolution of ordered systems (biological life) on Earth. …

A Feb. 10, 2015 University of Illinois College of Engineering news release (also on EurekAlert), which originated the news item, provides more detail about the theory and the research,

MEPP may have profound implications for our understanding of the evolution of biological life on Earth and of the underlying rules that govern the behavior and evolution of all nonequilibrium systems. Life emerged on Earth from the strongly nonequilibrium energy distribution created by the Sun’s hot photons striking a cooler planet. Plants evolved to capture high energy photons and produce heat, generating entropy. Then animals evolved to eat plants increasing the dissipation of heat energy and maximizing entropy production.

In their experiment, the researchers suspended a large number of carbon nanotubes in a non-conducting non-polar fluid and drove the system out of equilibrium by applying a strong electric field. Once electrically charged, the system evolved toward maximum entropy through two distinct intermediate states, with the spontaneous emergence of self-assembled conducting nanotube chains.

In the first state, the “avalanche” regime, the conductive chains aligned themselves according to the polarity of the applied voltage, allowing the system to carry current and thus to dissipate heat and produce entropy. The chains appeared to sprout appendages as nanotubes aligned themselves so as to adjoin adjacent parallel chains, effectively increasing entropy production. But frequently, this self-organization was destroyed through avalanches triggered by the heating and charging that emanates from the emerging electric current streams. (…)

“The avalanches were apparent in the changes of the electric current over time,” said Bezryadin.

“Toward the final stages of this regime, the appendages were not destroyed during the avalanches, but rather retracted until the avalanche ended, then reformed their connection. So it was obvious that the avalanches correspond to the ‘feeding cycle’ of the ‘nanotube inset’,” comments Bezryadin.

In the second relatively stable stage of evolution, the entropy production rate reached maximum or near maximum. This state is quasi-stable in that there were no destructive avalanches.

The study points to a possible classification scheme for evolutionary stages and a criterium for the point at which evolution of the system is irreversible—wherein entropy production in the self-organizing subsystem reaches its maximum possible value. Further experimentation on a larger scale is necessary to affirm these underlying principals, but if they hold true, they will prove a great advantage in predicting behavioral and evolutionary trends in nonequilibrium systems.

The authors draw an analogy between the evolution of intelligent life forms on Earth and the emergence of the wiggling bugs in their experiment. The researchers note that further quantitative studies are needed to round out this comparison. In particular, they would need to demonstrate that their “wiggling bugs” can multiply, which would require the experiment be reproduced on a significantly larger scale.

Such a study, if successful, would have implications for the eventual development of technologies that feature self-organized artificial intelligence, an idea explored elsewhere by co-author Alfred Hubler, funded by the Defense Advanced Research Projects Agency [DARPA]. [emphasis mine]

“The general trend of the evolution of biological systems seems to be this: more advanced life forms tend to dissipate more energy by broadening their access to various forms of stored energy,” Bezryadin proposes. “Thus a common underlying principle can be suggested between our self-organized clouds of nanotubes, which generate more and more heat by reducing their electrical resistance and thus allow more current to flow, and the biological systems which look for new means to find food, either through biological adaptation or by inventing more technologies.

“Extended sources of food allow biological forms to further grow, multiply, consume more food and thus produce more heat and generate entropy. It seems reasonable to say that real life organisms are still far from the absolute maximum of the entropy production rate. In both cases, there are ‘avalanches’ or ‘extinction events’, which set back this evolution. Only if all free energy given by the Sun is consumed, by building a Dyson sphere for example, and converted into heat then a definitely stable phase of the evolution can be expected.”

“Intelligence, as far as we know, is inseparable from life,” he adds. “Thus, to achieve artificial life or artificial intelligence, our recommendation would be to study systems which are far from equilibrium, with many degrees of freedom—many building blocks—so that they can self-organize and participate in some evolution. The entropy production criterium appears to be the guiding principle of the evolution efficiency.”

I am fascinated

  • (a) because this piece took an unexpected turn onto the topic of artificial life/artificial intelligence,
  • (b) because of my longstanding interest in artificial life/artificial intelligence,
  • (c) because of the military connection, and
  • (d) because this is the first time I’ve come across something that provides a bridge from fundamental particles to nanoparticles.

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

Self-Assembled Wiggling Nano-Structures and the Principle of Maximum Entropy Production by A. Belkin, A. Hubler, & A. Bezryadin. Scientific Reports 5, Article number: 8323 doi:10.1038/srep08323 Published 09 February 2015

Adding to my delight, this paper is open access.

Watching buckyballs (buckminsterfullerenes) self-assemble in real-time

For the 5% or less of the world who need this explanation, the reference to a football later in this post is, in fact, a reference to a soccer ball. Moving on to a Nov. 5, 2014 news item on Nanowerk (Note: A link has been removed),

Using DESY’s ultrabright X-ray source PETRA III, researchers have observed in real-time how football-shaped carbon molecules arrange themselves into ultra-smooth layers. Together with theoretical simulations, the investigation reveals the fundamentals of this growth process for the first time in detail, as the team around Sebastian Bommel (DESY and Humboldt Universität zu Berlin) and Nicola Kleppmann (Technische Universität Berlin) reports in the scientific journal Nature Communications (“Unravelling the multilayer growth of the fullerene C60 in real-time”).

This knowledge will eventually enable scientists to tailor nanostructures from these carbon molecules for certain applications, which play an increasing role in the promising field of plastic electronics. The team consisted of scientists from Humboldt-Universität zu Berlin, Technische Universität Berlin, Universität Tübingen and DESY.

Here’s an image of the self-assembling materials,

Caption: This is an artist's impression of the multilayer growth of buckyballs. Credit: Nicola Kleppmann/TU Berlin

Caption: This is an artist’s impression of the multilayer growth of buckyballs.
Credit: Nicola Kleppmann/TU Berlin

A Nov. 5, 2014 DESY (Deutsches Elektronen-Synchrotron) press release (also on EurekAlert), describes the work further,

The scientists studied so called buckyballs. Buckyballs are spherical molecules, which consist of 60 carbon atoms (C60). Because they are reminiscent of American architect Richard Buckminster Fuller’s geodesic domes, they were christened buckminsterfullerenes or “buckyballs” for short. With their structure of alternating pentagons and hexagons, they also resemble tiny molecular footballs. [emphasis mine]

Using DESY’s X-ray source PETRA III, the researchers observed how buckyballs settle on a substrate from a molecular vapour. In fact, one layer after another, the carbon molecules grow predominantly in islands only one molecule high and barely form tower-like structures..“The first layer is 99% complete before 1% of the second layer is formed,” explains DESY researcher Bommel, who is completing his doctorate in Prof. Stefan Kowarik’s group at the Humboldt Universität zu Berlin. This is how extremely smooth layers form.

“To really observe the growth process in real-time, we needed to measure the surfaces on a molecular level faster than a single layer grows, which takes place in about a minute,” says co-author Dr. Stephan Roth, head of the P03 measuring station, where the experiments were carried out. “X-ray investigations are well suited, as they can trace the growth process in detail.”

“In order to understand the evolution of the surface morphology at the molecular level, we carried out extensive simulations in a non-equilibrium system. These describe the entire growth process of C60 molecules into a lattice structure,” explains Kleppmann, PhD student in Prof. Sabine Klapp’s group at the Institute of Theoretical Physics, Technische Universität Berlin. “Our results provide fundamental insights into the molecular growth processes of a system that forms an important link between the world of atoms and that of colloids.”

Through the combination of experimental observations and theoretical simulations, the scientists determined for the first time three major energy parameters simultaneously for such a system: the binding energy between the football molecules, the so-called “diffusion barrier,” which a molecule must overcome if it wants to move on the surface, and the Ehrlich-Schwoebel barrier, which a molecule must overcome if it lands on an island and wants to hop down from that island.

“With these values, we now really understand for the first time how such nanostructures come into existence,” stresses Bommel. “Using this knowledge, it is conceivable that these structures can selectively be grown in the future: How must I change my temperature and deposition rate parameters so that an island of a particular size will grow. This could, for example, be interesting for organic solar cells, which contain C60.” The researchers intend to explore the growth of other molecular systems in the future using the same methods.

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

Unravelling the multilayer growth of the ​fullerene C60 in real time by S. Bommel, N. Kleppmann, C. Weber, H. Spranger, P. Schäfer, J. Novak, S.V. Roth, F. Schreiber, S.H.L. Klapp, & S. Kowarik. Nature Communications 5, Article number: 5388 doi:10.1038/ncomms6388 Published 05 November 2014

This article is open access.

I was not able to find any videos of these buckyballs assembling in real-time. Presumably, there are technical issues with recording the process, financial issues, or some combination thereof. Still, I can’t help but feel teased (tongue in cheek) by these scientists who give me an artist’s concept instead. Hopefully, budgets and/or technology will allow the rest of us to view this process at some time in the future.

Self-assembling and disassembling nanotrain network

A Nov. 11, 2013 University of Oxford news release (also on EurekAlert dated as Nov. 10, 2013) highlights the first item I’ve seen about a nanostructure which both assembles and disassembles itself,

Tiny self-assembling transport networks, powered by nano-scale motors and controlled by DNA, have been developed by scientists at Oxford University and Warwick University.

The system can construct its own network of tracks spanning tens of micrometres in length, transport cargo across the network and even dismantle the tracks.

Researchers were inspired by the melanophore, used by fish cells to control their colour. Tracks in the network all come from a central point, like the spokes of a bicycle wheel. Motor proteins transport pigment around the network, either concentrating it in the centre or spreading it throughout the network. Concentrating pigment in the centre makes the cells lighter, as the surrounding space is left empty and transparent.

The researchers have provided an image,

Nanotrain network created by scientists at Oxford University: green dye-carrying shuttles after 'refuelling' with ATP travel towards the center of the network with their cargoes of green dye. Credit: Adam Wollman/Oxford University

Nanotrain network created by scientists at Oxford University: green dye-carrying shuttles after ‘refuelling’ with ATP travel towards the center of the network with their cargoes of green dye. Credit: Adam Wollman/Oxford University

The news release goes on to describe the system,

The system developed by the Oxford University team is very similar [to the melanophore used by fish cells], and is built from DNA and a motor protein called kinesin. Powered by ATP fuel, kinesins move along the micro-tracks carrying control modules made from short strands of DNA. ‘Assembler’ nanobots are made with two kinesin proteins, allowing them to move tracks around to assemble the network, whereas the ‘shuttles’ only need one kinesin protein to travel along the tracks.

‘DNA is an excellent building block for constructing synthetic molecular systems, as we can program it to do whatever we need,’ said Adam Wollman, who conducted the research at Oxford University’s Department of Physics. ‘We design the chemical structures of the DNA strands to control how they interact with each other. The shuttles can be used to either carry cargo or deliver signals to tell other shuttles what to do.

‘We first use assemblers to arrange the track into ‘spokes’, triggered by the introduction of ATP. We then send in shuttles with fluorescent green cargo which spread out across the track, covering it evenly. When we add more ATP, the shuttles all cluster in the centre of the track where the spokes meet. Next, we send signal shuttles along the tracks to tell the cargo-carrying shuttles to release the fluorescent cargo into the environment, where it disperses. We can also send shuttles programmed with ‘dismantle’ signals to the central hub, telling the tracks to break up.’

This demonstration used fluorescent green dyes as cargo, but the same methods could be applied to other compounds. As well as colour changes, spoke-like track systems could be used to speed up chemical reactions by bringing the necessary compounds together at the central hub. More broadly, using DNA to control motor proteins could enable the development of more sophisticated self-assembling systems for a wide variety of applications.

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

Transport and self-organization across different length scales powered by motor proteins and programmed by DNA by Adam J. M. Wollman, Carlos Sanchez-Cano, Helen M. J. Carstairs, Robert A. Cross, & Andrew J. Turberfield. Nature Nanotechnology (2013) doi:10.1038/nnano.2013.230 Published online 10 November 2013

This article is behind a paywall although you can preview it for free via ReadCube Access.

Self-assembling chains of nanoparticles

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

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

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.