Emulating -- and surpassing -- nature: Using DNA to build nanomaterials with desired properties

ScienceDaily (Oct. 13, 2011) — Nature is a master builder. Using a bottom-up approach, nature takes tiny atoms and, through chemical bonding, makes crystalline materials, like diamonds, silicon and even table salt. In all of them, the properties of the crystals depend upon the type and arrangement of atoms within the crystalline lattice.

Now, a team of Northwestern University scientists has learned how to top nature by building crystalline materials from nanoparticles and DNA, the same material that defines the genetic code for all living organisms.

Using nanoparticles as "atoms" and DNA as "bonds," the scientists have learned how to create crystals with the particles arranged in the same types of atomic lattice configurations as some found in nature, but they also have built completely new structures that have no naturally occurring mineral counterpart.

The basic design rules the Northwestern scientists have established for this approach to nanoparticle assembly promise the possibility of creating a variety of new materials that could be useful in catalysis, electronics, optics, biomedicine and energy generation, storage and conversion technologies.

The new method and design rules for making crystalline materials from nanostructures and DNA will be published Oct. 14 by the journal Science.

"We are building a new periodic table of sorts," said Professor Chad A. Mirkin, who led the research. "Using these new design rules and nanoparticles as 'artificial atoms,' we have developed modes of controlled crystallization that are, in many respects, more powerful than the way nature and chemists make crystalline materials from atoms. By controlling the size, shape, type and location of nanoparticles within a given lattice, we can make completely new materials and arrangements of particles, not just what nature dictates."

Mirkin is the George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences and professor of medicine, chemical and biological engineering, biomedical engineering and materials science and engineering and director of Northwestern's International Institute for Nanotechnology (IIN).

"Once we have a certain type of lattice," Mirkin said, "the particles can be moved closer together or farther apart by changing the length of the interconnecting DNA, thereby providing near-infinite tunability."

"This work resulted from an interdisciplinary collaboration that coupled synthetic chemistry with theoretical model building," said coauthor George C. Schatz, a theoretician and the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern. "It was the back and forth between synthesis and theory that was crucial to the development of the design rules. Collaboration is a special aspect of research at Northwestern, and it worked very effectively for this project."

In the study, the researchers start with two solutions of nanoparticles coated with single-stranded DNA. They then add DNA strands that bind to these DNA-functionalized particles, which then present a large number of DNA "sticky ends" at a controlled distance from the particle surface; these sticky ends then bind to the sticky ends of adjacent particles, forming a macroscopic arrangement of nanoparticles.

Different crystal structures are achieved by using different combinations of nanoparticles (with varying sizes) and DNA linker strands (with controllable lengths). After a process of mixing and heating, the assembled particles transition from an initially disordered state to one where every particle is precisely located according to a crystal lattice structure. The process is analogous to how ordered atomic crystals are formed.

The researchers report six design rules that can be used to predict the relative stability of different structures for a given set of nanoparticle sizes and DNA lengths. In the paper, they use these rules to prepare 41 different crystal structures with nine distinct crystal symmetries. However, the design rules outline a strategy to independently adjust each of the relevant crystallographic parameters, including particle size (varied from 5 to 60 nanometers), crystal symmetry and lattice parameters (which can range from 20 to 150 nanometers). This means that these 41 crystals are just a small example of the near infinite number of lattices that could be created using different nanoparticles and DNA strands.

Mirkin and his team used gold nanoparticles in their work but note that their method also can be applied to nanoparticles of other chemical compositions. Both the type of nanoparticle assembled and the symmetry of the assembled structure contribute to the properties of a lattice, making this method an ideal means to create materials with predictable and controllable physical properties.

Mirkin believes that, one day soon, software will be created that allows scientists to pick the particle and DNA pairs required to make almost any structure on demand.

The Air Force Office of Scientific Research, the U.S. Department of Energy Office of Basic Energy Sciences and the National Science Foundation supported the research.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Northwestern University, via EurekAlert!, a service of AAAS.

Journal Reference:

R. J. Macfarlane, B. Lee, M. R. Jones, N. Harris, G. C. Schatz, C. A. Mirkin. Nanoparticle Superlattice Engineering with DNA. Science, 2011; 334 (6053): 204 DOI: 10.1126/science.1210493

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Simple compound with surprising antifreeze properties

ScienceDaily (Oct. 25, 2011) — A chemical compound used to stabilize particles in suspension has proved capable of controlling the growth of ice crystals. This finding was made by CNRS/Saint-Gobain researchers, in collaboration with CNRS-affiliated teams at INSA Lyon and Université Claude Bernard Lyon 1. Surprisingly, the compound in question is a simple molecule, not at all like the macromolecules previously known for their antifreeze properties. It offers many advantages, including low production costs, stability and ease of use, which should open the way to industrial applications.

Published in the online journal PLoS ONE, this work also provides new leads for the development of synthetic equivalents of antifreeze proteins, different from those currently produced.

The formation of ice crystals can have multiple, and often destructive, consequences. Cell degradation in living organisms, damage to land and roads in cold climates, ice crystals in ice creams… These are all examples of situations where it is useful to control ice growth. Many organisms and species that live in cold environments have adapted to control ice growth. Their resistance to low temperatures is based on the presence of antifreeze proteins, all of which are made up of very long organic chains with amphiphilic structures (partly hydrophilic, partly hydrophobic). How do these proteins interact with ice crystals? Researchers are trying to identify the mechanism enabling antifreeze proteins to identify these crystals, but the phenomenon is still not fully understood. In addition, since these proteins are extremely costly to extract, the preferred solution is to create synthetic equivalents inspired by natural structures. All proteins currently known for their "antifreeze" properties are macromolecules (like glycoproteins, polysaccharides, etc.).

A team led by Sylvain Deville(1), CNRS researcher at the LSFC (Laboratoire de Synthèse et Fonctionnalisation des Céramiques, Synthesis and Functionalization of Ceramics Laboratory, CNRS/Saint-Gobain), in collaboration with the Matériaux, Ingénierie et Sciences (Materials, Engineering and Sciences) laboratory (CNRS/INSA Lyon / Université Claude Bernard Lyon 1), has discovered that zirconium acetate, a chemical compound normally used to stabilize particles in suspension, can control ice crystal growth. The compound governs the morphology of the ice crystals obtained by freezing a solution in which it is combined with water. The crystals obtained when adding zirconium acetate are very homogenous, whereas those obtained without it show no particular uniformity.

These results are quite surprising, given that zirconium acetate is a "salt,"(2) a simple compound that is radically different from the macromolecules known for their antifreeze properties. It was not known as a substance capable of controlling ice crystal growth. Such control can be exerted in a number of ways: by reducing the speed of crystal growth (to slow their formation), by lowering the freezing point (to delay their formation), or by controlling their morphology, as in this case. Since this implies a direct interaction with the ice crystals, the researchers were surprised to find out that such radically different molecules as zirconium acetate and proteins could affect crystalline growth.

This compound offers significant advantages over existing equivalents, whether natural or synthetic. It is cheap to produce, stable, "simple" and easy to use, which bodes well for a wealth of future industrial applications. In addition, since it is totally different from all previously identified and/or developed substances with the same function, further research could lead to the development of other molecules with antifreeze properties.

This project relied on X-ray diffraction and imaging. These works were made possible by using the X-ray synchrotron (beam line ID19) at the ESRF in Grenoble, France. They are covered by two patents published on October 1, 2011.

Notes:

Laureate of an ERC Junior grant in 2011.In chemistry, a salt is an ionic compound made up of cations and anions, forming a neutral product with no net charge. This type of salt is much different from edible (table) salt.

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The above story is reprinted from materials provided by CNRS (Délégation Paris Michel-Ange), via AlphaGalileo.

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Journal Reference:

Sylvain Deville, Céline Viazzi, Jérôme Leloup, Audrey Lasalle, Christian Guizard, Eric Maire, Jérôme Adrien, Laurent Gremillard. Ice Shaping Properties, Similar to That of Antifreeze Proteins, of a Zirconium Acetate Complex. PLoS ONE, 2011; 6 (10): e26474 DOI: 10.1371/journal.pone.0026474

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Researchers discover material with graphene-like properties

ScienceDaily (Oct. 14, 2011) — After the Nobel Prize in Physics was awarded to two scientists in 2010 who had studied the material graphene, this substance has received a lot of attention. Together with colleagues from Korea, Dr. Frederik Wolff-Fabris from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now developed and analyzed a material which possesses physical properties similar to graphene. Its structure also resembles iron pnictides, i.e. high temperature superconductors, and it definitely has a promising future: Due to the position of the individual components in the Periodic Table of Elements, some of the atoms can simply be replaced by foreign atoms.

This creates new materials which can be superconductive, magnetic, or behave like topological insulators.

Earlier this year, Dr. Jun Sung Kim came from South Korea to use HZDR's Dresden High Magnetic Field Laboratory to analyze a number of material samples in high magnetic fields. For the first time ever, he and his colleague from Dresden, Dr. Frederik Wolff-Fabris, studied the metal SrMnBi2 and observed something amazing: The material consisting of the three elements strontium, manganese, and bismuth behaves physically similar to the "magical material" graphene.

Due to its composition and the position of its elements in the Periodic Table, SrMnBi2 permits simple and uncomplicated doping with foreign atoms. Inserting small amounts of foreign atoms alters the physical properties of a material. This might result in the creation of new magnets or superconductors.

SrMnBi2 is currently also in the focus of other research groups; but only the use of ultra-high magnetic fields, such as those generated in the Dresden High Magnetic Field Laboratory, permitted these precise results and, thus, a publication in the scientific journal Physical Review Letters. Later this year, Dr. Jun Sung Kim will return to Dresden to conduct additional experiments on SrMnBi2 with Dr. Wolff-Fabris.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Helmholtz Association of German Research Centres.

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Joonbum Park, G. Lee, F. Wolff-Fabris, Y. Koh, M. Eom, Y. Kim, M. Farhan, Y. Jo, C. Kim, J. Shim, J. Kim. Anisotropic Dirac Fermions in a Bi Square Net of SrMnBi2. Physical Review Letters, 2011; 107 (12) DOI: 10.1103/PhysRevLett.107.126402

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How graphene's electrical properties can be tuned

ScienceDaily (Sep. 26, 2011) — An accidental discovery in a physicist's laboratory at the University of California, Riverside provides a unique route for tuning the electrical properties of graphene, nature's thinnest elastic material. This route holds great promise for replacing silicon with graphene in the microchip industry.

The researchers found that stacking up three layers of graphene, like pancakes, significantly modifies the material's electrical properties. When they fabricated trilayer graphene in the lab and measured its conductance, they found, to their surprise, that depending on how the layers were stacked some of the trilayer graphene devices were conducting while others were insulating.

"What we stumbled upon is a simple and convenient 'knob' for tuning graphene sheets' electrical properties," said Jeanie Lau, an associate professor of physics and astronomy, whose lab made the serendipitous finding.

Study results appeared online Sept. 25 in Nature Physics.

Graphene is a one-atom thick sheet of carbon atoms arranged in hexagonal rings. Bearing excellent material properties, such as high current-carrying capacity and thermal conductivity, this "wonder material" is ideally suited for creating components for semiconductor circuits and computers.

Because of the planar and chicken wire-like structure of graphene, its sheets lend themselves well to stacking in what is called 'Bernal stacking,' the stacking fashion of graphene sheets.

In a Bernal-stacked bilayer, one corner of the hexagons of the second sheet is located above the center of the hexagons of the bottom sheet. In Bernal-stacked trilayer (ABA), the top (third) sheet is exactly on top of the lowest sheet. In rhombohedral-stacked (ABC) trilayer, the top sheet is shifted by the distance of an atom, so that the top (third) sheet and the lowest sheet form a Bernal stacking as well.

"The most stable form of trilayer graphene is ABA, which behaves like a metal," Lau explained. "Amazingly, if we simply shift the entire topmost layer by the distance of a single atom, the trilayer -- now with ABC or rhombohedral stacking -- becomes insulating. Why this happens is not clear as yet. It could be induced by electronic interactions. We eagerly await an explanation from theorists!"

Her lab used Raman spectroscopy to examine the graphene devices' stacking orders. Next the lab plans to investigate the nature of the insulating state in ABC-stacked graphene. In this kind of stacked graphene, they also plan to study the band gap -- a range in energy, critical for digital applications, in which no electrons can exist.

"The presence of the gap in ABC-stacked graphene that arises, we believe, from enhanced electronic interactions is interesting since it is not expected from theoretical calculations," Lau said. "Understanding this gap is particularly important for the major challenge of band gap engineering in graphene electronics."

Besides graphene, Lau studies nanowires and carbon nanotubes. Her research has helped physicists gain fundamental understanding of how atoms and electrons behave when they are ruled by quantum mechanics. Her lab studies novel electrical properties that arise from the quantum confinement of atoms and charges to nanoscale systems. Her research team has shown that graphene can act as an atomic-scale billiard table, with electric charges acting as billiard balls.

Her other research interests include superconductivity, thermal management and electronic transport in nanostructures, and engineering new classes of nanoscale devices.

An educational component of Lau's research effort is the active involvement of high school, undergraduate, and graduate students, especially minority and women, in her cutting-edge research, taking advantage of the ethnic diversity of UCR's student population and local communities. She is a founding faculty member of the UCR Undergraduate Research Journal. She also organized a "Women in Physics" lunch group that provides a friendly platform for female students, postdocs and faculty members to interact.

After receiving her bachelor's degree in physics from the University of Chicago in 1994, Lau proceeded to Harvard University from where she received her master's and doctoral degrees in physics in 1997 and 2001, respectively. She joined UCR in 2004, after an appointment as a research associate in the Hewlett-Packard Laboratory.

Lau's awards and honors include a Presidential Early Career Award for Scientists and Engineers, 2009; a National Science Foundation CAREER Award, 2008; the Richter Fellowship for Undergraduate Research, 1992; a David W. Grainger Senior Scholarship, 1993; and a Robert T. Poe Faculty Development Grant from the Chinese-American Faculty Association of Southern California, 2007. She has published more than 60 research articles in peer-reviewed journals.

Lau, a member of UCR's Center for Nanoscale Science and Engineering, was joined in the research by W. Bao (the first author of the research paper), L. Jing, J. Velasco Jr., Y. Lee, G. Liu, D. Tran and M. Bockrath at UCR; B. Stanley at Caltech; M. Aykol and S. B. Cronin at the University of Southern California; D. Smirnov at the National High Magnetic Field Laboratory, Fla.; M. Koshino at Tohoku University, Japan; and E. McCann at Lancaster University, United Kingdom.

The research was funded by grants from the National Science Foundation, Office of Naval Research, and the Focus Center for Functional Engineered Nano Architectonics.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Riverside.

Journal Reference:

W. Bao, L. Jing, J. Velasco, Y. Lee, G. Liu, D. Tran, B. Standley, M. Aykol, S. B. Cronin, D. Smirnov, M. Koshino, E. McCann, M. Bockrath, C. N. Lau. Stacking-dependent band gap and quantum transport in trilayer graphene. Nature Physics, 2011; DOI: 10.1038/nphys2103

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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How graphene's electrical properties can be tuned

ScienceDaily (Sep. 26, 2011) — An accidental discovery in a physicist's laboratory at the University of California, Riverside provides a unique route for tuning the electrical properties of graphene, nature's thinnest elastic material. This route holds great promise for replacing silicon with graphene in the microchip industry.

The researchers found that stacking up three layers of graphene, like pancakes, significantly modifies the material's electrical properties. When they fabricated trilayer graphene in the lab and measured its conductance, they found, to their surprise, that depending on how the layers were stacked some of the trilayer graphene devices were conducting while others were insulating.

"What we stumbled upon is a simple and convenient 'knob' for tuning graphene sheets' electrical properties," said Jeanie Lau, an associate professor of physics and astronomy, whose lab made the serendipitous finding.

Study results appeared online Sept. 25 in Nature Physics.

Graphene is a one-atom thick sheet of carbon atoms arranged in hexagonal rings. Bearing excellent material properties, such as high current-carrying capacity and thermal conductivity, this "wonder material" is ideally suited for creating components for semiconductor circuits and computers.

Because of the planar and chicken wire-like structure of graphene, its sheets lend themselves well to stacking in what is called 'Bernal stacking,' the stacking fashion of graphene sheets.

In a Bernal-stacked bilayer, one corner of the hexagons of the second sheet is located above the center of the hexagons of the bottom sheet. In Bernal-stacked trilayer (ABA), the top (third) sheet is exactly on top of the lowest sheet. In rhombohedral-stacked (ABC) trilayer, the top sheet is shifted by the distance of an atom, so that the top (third) sheet and the lowest sheet form a Bernal stacking as well.

"The most stable form of trilayer graphene is ABA, which behaves like a metal," Lau explained. "Amazingly, if we simply shift the entire topmost layer by the distance of a single atom, the trilayer -- now with ABC or rhombohedral stacking -- becomes insulating. Why this happens is not clear as yet. It could be induced by electronic interactions. We eagerly await an explanation from theorists!"

Her lab used Raman spectroscopy to examine the graphene devices' stacking orders. Next the lab plans to investigate the nature of the insulating state in ABC-stacked graphene. In this kind of stacked graphene, they also plan to study the band gap -- a range in energy, critical for digital applications, in which no electrons can exist.

"The presence of the gap in ABC-stacked graphene that arises, we believe, from enhanced electronic interactions is interesting since it is not expected from theoretical calculations," Lau said. "Understanding this gap is particularly important for the major challenge of band gap engineering in graphene electronics."

Besides graphene, Lau studies nanowires and carbon nanotubes. Her research has helped physicists gain fundamental understanding of how atoms and electrons behave when they are ruled by quantum mechanics. Her lab studies novel electrical properties that arise from the quantum confinement of atoms and charges to nanoscale systems. Her research team has shown that graphene can act as an atomic-scale billiard table, with electric charges acting as billiard balls.

Her other research interests include superconductivity, thermal management and electronic transport in nanostructures, and engineering new classes of nanoscale devices.

An educational component of Lau's research effort is the active involvement of high school, undergraduate, and graduate students, especially minority and women, in her cutting-edge research, taking advantage of the ethnic diversity of UCR's student population and local communities. She is a founding faculty member of the UCR Undergraduate Research Journal. She also organized a "Women in Physics" lunch group that provides a friendly platform for female students, postdocs and faculty members to interact.

After receiving her bachelor's degree in physics from the University of Chicago in 1994, Lau proceeded to Harvard University from where she received her master's and doctoral degrees in physics in 1997 and 2001, respectively. She joined UCR in 2004, after an appointment as a research associate in the Hewlett-Packard Laboratory.

Lau's awards and honors include a Presidential Early Career Award for Scientists and Engineers, 2009; a National Science Foundation CAREER Award, 2008; the Richter Fellowship for Undergraduate Research, 1992; a David W. Grainger Senior Scholarship, 1993; and a Robert T. Poe Faculty Development Grant from the Chinese-American Faculty Association of Southern California, 2007. She has published more than 60 research articles in peer-reviewed journals.

Lau, a member of UCR's Center for Nanoscale Science and Engineering, was joined in the research by W. Bao (the first author of the research paper), L. Jing, J. Velasco Jr., Y. Lee, G. Liu, D. Tran and M. Bockrath at UCR; B. Stanley at Caltech; M. Aykol and S. B. Cronin at the University of Southern California; D. Smirnov at the National High Magnetic Field Laboratory, Fla.; M. Koshino at Tohoku University, Japan; and E. McCann at Lancaster University, United Kingdom.

The research was funded by grants from the National Science Foundation, Office of Naval Research, and the Focus Center for Functional Engineered Nano Architectonics.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Riverside.

Journal Reference:

W. Bao, L. Jing, J. Velasco, Y. Lee, G. Liu, D. Tran, B. Standley, M. Aykol, S. B. Cronin, D. Smirnov, M. Koshino, E. McCann, M. Bockrath, C. N. Lau. Stacking-dependent band gap and quantum transport in trilayer graphene. Nature Physics, 2011; DOI: 10.1038/nphys2103

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Amazing electrical properties in polymers discovered

ScienceDaily (Sep. 25, 2011) — Crystals and ceramics pale when compared to a material researchers at Oak Ridge National Laboratory discovered that has 10 times their piezoelectric effect, making it suitable for perhaps hundreds of everyday uses.

ORNL's Volker Urban and colleagues at Technical University Aachen in Germany noticed the reverse piezoelectric effect -- defined as creating a mechanical strain by applying an electrical voltage -- while conducting fundamental research on polymers. At first they didn't think about their observations in terms of classic piezoelectric materials, but then they became more curious.

"We thought about comparing the effects that we observed to more 'classic' piezoelectric materials and were surprised by how large the effects were by comparison," said Urban, a member of the Department of Energy lab's Neutron Scattering Science Division.

Until now, scientists did not believe that non-polar polymers were capable of exhibiting any piezoelectric effect, which occurs only in non-conductive materials. This research, however, shows up to 10 times the measured electro-active response as compared to the strongest known piezoelectric materials, typically crystals and ceramics.

"We observed this effect when two different polymer molecules like polystyrene and rubber are coupled as two blocks in a di-block copolymer," Urban said.

Temperature-dependent studies of the molecular structure revealed an intricate balance of the repulsion between the unlike blocks and an elastic restoring force found in rubber. The electric field adds a third force that can shift the intricate balance, leading to the piezoelectric effect.

"The extraordinarily large response could revolutionize the field of electro-active devices," said Urban, who listed a number of examples, including sensors, actuators, energy storage devices, power sources and biomedical devices. Urban also noted that additional potential uses are likely as word of this discovery gets out and additional research is performed.

"Ultimately, we're not sure where this finding will take us, but at the very least it provides a fundamentally new perspective in polymer science," Urban said.

The paper was published recently as the cover article in Advanced Materials. In addition to Urban, other authors are Markus Ruppel and Jimmy Mays of ORNL and Kristin Schmidt of the University of California at Santa Barbara. Authors from Aachen University are Christian Pester, Heiko Schoberth, Clemens Liedel, Patrick van Rijn, Kerstin Schindler, Stephanie Hiltl, Thomas Czubak and Alexander Böker.

Funding for this research was provided by DOE's Office of Science and the German Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Oak Ridge National Laboratory.

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Christian W. Pester, Markus Ruppel, Heiko G. Schoberth, Kristin Schmidt, Clemens Liedel, Patrick van Rijn, Kerstin A. Schindler, Stephanie Hiltl, Thomas Czubak, Jimmy Mays, Volker S. Urban, Alexander Böker. Piezoelectric Properties of Non-Polar Block Copolymers. Advanced Materials, 2011; 23 (35): 4047 DOI: 10.1002/adma.201102192

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Amazing electrical properties in polymers discovered

ScienceDaily (Sep. 25, 2011) — Crystals and ceramics pale when compared to a material researchers at Oak Ridge National Laboratory discovered that has 10 times their piezoelectric effect, making it suitable for perhaps hundreds of everyday uses.

ORNL's Volker Urban and colleagues at Technical University Aachen in Germany noticed the reverse piezoelectric effect -- defined as creating a mechanical strain by applying an electrical voltage -- while conducting fundamental research on polymers. At first they didn't think about their observations in terms of classic piezoelectric materials, but then they became more curious.

"We thought about comparing the effects that we observed to more 'classic' piezoelectric materials and were surprised by how large the effects were by comparison," said Urban, a member of the Department of Energy lab's Neutron Scattering Science Division.

Until now, scientists did not believe that non-polar polymers were capable of exhibiting any piezoelectric effect, which occurs only in non-conductive materials. This research, however, shows up to 10 times the measured electro-active response as compared to the strongest known piezoelectric materials, typically crystals and ceramics.

"We observed this effect when two different polymer molecules like polystyrene and rubber are coupled as two blocks in a di-block copolymer," Urban said.

Temperature-dependent studies of the molecular structure revealed an intricate balance of the repulsion between the unlike blocks and an elastic restoring force found in rubber. The electric field adds a third force that can shift the intricate balance, leading to the piezoelectric effect.

"The extraordinarily large response could revolutionize the field of electro-active devices," said Urban, who listed a number of examples, including sensors, actuators, energy storage devices, power sources and biomedical devices. Urban also noted that additional potential uses are likely as word of this discovery gets out and additional research is performed.

"Ultimately, we're not sure where this finding will take us, but at the very least it provides a fundamentally new perspective in polymer science," Urban said.

The paper was published recently as the cover article in Advanced Materials. In addition to Urban, other authors are Markus Ruppel and Jimmy Mays of ORNL and Kristin Schmidt of the University of California at Santa Barbara. Authors from Aachen University are Christian Pester, Heiko Schoberth, Clemens Liedel, Patrick van Rijn, Kerstin Schindler, Stephanie Hiltl, Thomas Czubak and Alexander Böker.

Funding for this research was provided by DOE's Office of Science and the German Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Christian W. Pester, Markus Ruppel, Heiko G. Schoberth, Kristin Schmidt, Clemens Liedel, Patrick van Rijn, Kerstin A. Schindler, Stephanie Hiltl, Thomas Czubak, Jimmy Mays, Volker S. Urban, Alexander Böker. Piezoelectric Properties of Non-Polar Block Copolymers. Advanced Materials, 2011; 23 (35): 4047 DOI: 10.1002/adma.201102192

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Synthetic collagen from maize has human properties

ScienceDaily (June 28, 2011) — Synthetic collagen has a wide range of applications in reconstructive and cosmetic surgery and in the food industry. For proper function in animals a certain number of prolines within the protein need to be hydroxylated. BioMed Central's open access journal BMC Biotechnology reports that for the first time the a1 chain of type 1 collagen has been produced in maize with similar levels of proline hydroxylation to human collagen.

Most collagen used is derived from animals but there are risks associated with this collagen containing infectious agents or being rejected by the body. To avoid this problem several laboratory-based systems have been developed using plants to produce collagen. Plant-derived recombinant proteins should have lower contamination and fewer infectious agents, but these systems are unable to make modifications to the protein essential for proper function in human cells.

Working in collaboration with industrial partners researchers added a gene, which codes for the a1 chain of human CI (hCI a1), to maize along with genes which make human prolyl 4-hydroxylase. This second protein was able to hydroxylate approximately the same percentage of prolines in the recombinant collagen a1 chain, produced in maize, as seen for human collagen made in human cells.

Dr Kan Wang from Iowa State University said, "Producing human collagen in maize seeds is an inexpensive alternative to using animal-derived collagen. The seeds are easy to grow, process, and store. Our transgenic plant system is also able to produce a protein with human-like modifications making it a better choice for a wide range of applications."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by BioMed Central, via EurekAlert!, a service of AAAS.

Journal Reference:

Xing Xu, Qinglei Gan, Richard C Clough, Kamesh M Pappu, John A Howard, Julio A Baez, Kan Wang. Hydroxylation of recombinant human collagen type I alpha 1 in transgenic maize co-expressed with a recombinant human prolyl 4-hydroxylase. BMC Biotechnology, 2011; 11 (1): 69 DOI: 10.1186/1472-6750-11-69

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Properties of 'confined' water within single-walled carbon nanotube pores clarified

ScienceDaily (June 23, 2011) — Water and ice may not be among the first things that come to mind when you think about single-walled carbon nanotubes (SWCNTs), but a Japan-based research team hoping to get a clearer understanding of the phase behavior of confined water in the cylindrical pores of carbon nanotubes zeroed in on confined water's properties and made some surprising discoveries.

The team, from Tokyo Metropolitan University, Nagoya University, Japan Science and Technology Agency, and National Institute of Advanced Industrial Science and Technology, describes their findings in the American Institute of Physics' Journal of Chemical Physics.

Although carbon nanotubes consist of hydrophobic (water repelling) graphene sheets, experimental studies on SWCNTs show that water can indeed be confined in open-ended carbon nanotubes.

This discovery gives us a deeper understanding of the properties of nanoconfined water within the pores of SWCNTs, which is a key to the future of nanoscience. It's anticipated that nanoconfined water within carbon nanotubes can open the door to the development of a variety of nifty new nanothings -- nanofiltration systems, molecular nanovalves, molecular water pumps, nanoscale power cells, and even nanoscale ferroelectric devices.

"When materials are confined at the atomic scale they exhibit unusual properties not otherwise observed, due to the so-called 'nanoconfinement effect.' In geology, for example, nanoconfined water provides the driving force for frost heaves in soil, and also for the swelling of clay minerals," explains Yutaka Maniwa, a professor in the Department of Physics at Tokyo Metropolitan University. "We experimentally studied this type of effect for water using SWCNTs."

Water within SWCNTs in the range of 1.68 to 2.40 nanometers undergoes a wet-dry type of transition when temperature is decreased. And the team discovered that when SWCNTs are extremely narrow, the water inside forms tubule ices that are quite different from any bulk ices known so far. Strikingly, their melting point rises as the SWCNT diameter decreases -- contrary to that of bulk water inside a large-diameter capillary. In fact, tubule ice occurred even at room temperature inside SWCNTs.

"We extended our studies to the larger diameter SWCNTs up to 2.40 nanometers and successfully proposed a global phase behavior of water," says Maniwa. "This phase diagram (see image) covers a crossover from microscopic to macroscopic regions. In the macroscopic region, a novel wet-dry transition was newly explored at low temperature."

Results such as these contribute to a greater understanding of fundamental science because nanoconfined water exists and plays a vital role everywhere on Earth -- including our bodies. "Understanding the nanoconfined effect on the properties of materials is also crucial to develop new devices, such as proton-conducting membranes and nanofiltration," Maniwa notes.

Next up, the team plans to investigate the physical properties of confined water discovered so far inside SWCNTs (such as dielectricity and proton conduction). They will pursue this to obtain a better understanding of the molecular structure and transport properties in biological systems.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Note: If no author is given, the source is cited instead.

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Finding answers century-old questions about platinum's catalytic properties

ScienceDaily (June 8, 2011) — Researchers now understand more about why platinum is so efficient at producing power in hydrogen fuel cells.

"Understanding platinum's properties for speeding up chemical reactions will potentially enable scientists to create significantly cheaper synthetic or metal alloy alternatives for use in sustainable devices like fuel cells," says Gregory Jerkiewicz, a professor in the Department of Chemistry who led the groundbreaking study, published in the journal Langmuir.

Dr. Jerkiewicz's research team has found that when platinum is used in reactions involving hydrogen it develops an embedded layer of hydrogen just one atom thick. This gives the platinum hydrophobic or water-repelling qualities, meaning that stray water molecules inside the fuel cell cannot bond strongly with the surface of the platinum.

The water-repelling nature of the modified platinum means that incoming hydrogen molecules can easily attach to the surface of the platinum and separate into smaller particles without requiring additional energy to displace any water molecules that are in the way.

The reduction in the energy required for hydrogen molecules to attach to the surface of the platinum means that the process is fast and efficient and the fuel cell can deliver a lot of power.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Queen's University.

Journal Reference:

Gregory Jerkiewicz, Gholamreza Vatankhah, Shin-ichi Tanaka, Jean Lessard. Discovery of the Potential of Minimum Mass for Platinum Electrodes. Langmuir, 2011; 27 (7): 4220 DOI: 10.1021/la200153n

Note: If no author is given, the source is cited instead.

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New properties of supercooled confined water discovered

ScienceDaily (May 12, 2011) — A study led by the UB researcher Giancarlo Franzese and published in the journal Physical Review Letters suggests that hydrophobic nanoconfinement can alter the thermodynamics of water at supercool temperatures. These findings may have important applications in fields related to conservation at cryogenic temperatures (around -100 ºC) -- for example, in the preservation of stem cells, blood and food products.

The team behind the study, led by Giancarlo Franzese from the UB's Department of Fundamental Physics, included researchers from Boston University and TU Berlin.

Water exhibits atypical fluid behaviour. One of its unique characteristics is the increase in heat capacity as water cools, an anomaly that enables us to regulate our body temperature. When water is supercooled -- that is, when it is in liquid state at a temperature below its melting point -- the range of anomalies expands. This irregular behaviour has generated fierce scientific debate over the last twenty years and could hold the key to understanding why water is so different to other liquids and why it is so important for biological organisms.

From a technical perspective, it is difficult to observe supercooled water directly and many researchers opt to use nanoconfinement. In this study, the team used Monte Carlo simulations to study a layer of water only one nanometre high -- approximately equivalent to the diameter of three water molecules -- confined between two hydrophobic plates. Hydrophobic nanoparticles were then added to the water layer in random positions to generate nanochannels or variable size.

This process led to a strong decrease in thermodynamic fluctuations, reflected in compressibility, thermal expansion coefficient and specific heat. The observed decrease occurred at all pressures tested, and at pressures in the region of 180 MPa fluctuations dropped by almost 99% for a concentration in nanoparticles of 25% by volume. The reduction was found to be as high as 90% even at a particle concentration ten times lower.

According to Giancarlo Franzese, the results show that the thermodynamic behaviour of water confined in hydrophobic nanochannels is very different to that of unconfined water, even allowing for the possible presence of more than one liquid phase within the range of temperatures and pressures tested.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Universidad de Barcelona, via AlphaGalileo.

Journal Reference:

Elena Strekalova, Marco Mazza, H. Stanley, Giancarlo Franzese. Large Decrease of Fluctuations for Supercooled Water in Hydrophobic Nanoconfinement. Physical Review Letters, 2011; 106 (14) DOI: 10.1103/PhysRevLett.106.145701

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New way to control conductivity: Reversible control of electrical and thermal properties could find uses in storage systems

ScienceDaily (May 5, 2011) — A team of researchers at MIT has found a way to manipulate both the thermal conductivity and the electrical conductivity of materials simply by changing the external conditions, such as the surrounding temperature. And the technique they found can change electrical conductivity by factors of well over 100, and heat conductivity by more than threefold.

"It's a new way of changing and controlling the properties" of materials -- in this case a class called percolated composite materials -- by controlling their temperature, says Gang Chen, MIT's Carl Richard Soderberg Professor of Power Engineering and director of the Pappalardo Micro and Nano Engineering Laboratories. Chen is the senior author of a paper describing the process that was published online on April 19 and will appear in a forthcoming issue of Nature Communications. The paper's lead authors are former MIT visiting scholars Ruiting Zheng of Beijing Normal University and Jinwei Gao of South China Normal University, along with current MIT graduate student Jianjian Wang. The research was partly supported by grants from the National Science Foundation.

The system Chen and his colleagues developed could be applied to many different materials for either thermal or electrical applications. The finding is so novel, Chen says, that the researchers hope some of their peers will respond with an immediate, "I have a use for that!"

One potential use of the new system, Chen explains, is for a fuse to protect electronic circuitry. In that application, the material would conduct electricity with little resistance under normal, room-temperature conditions. But if the circuit begins to heat up, that heat would increase the material's resistance, until at some threshold temperature it essentially blocks the flow, acting like a blown fuse. But then, instead of needing to be reset, as the circuit cools down the resistance decreases and the circuit automatically resumes its function.

Another possible application is for storing heat, such as from a solar thermal collector system, later using it to heat water or homes or to generate electricity. The system's much-improved thermal conductivity in the solid state helps it transfer heat.

Essentially, what the researchers did was suspend tiny flakes of one material in a liquid that, like water, forms crystals as it solidifies. For their initial experiments, they used flakes of graphite suspended in liquid hexadecane, but they showed the generality of their process by demonstrating the control of conductivity in other combinations of materials as well. The liquid used in this research has a melting point close to room temperature -- advantageous for operations near ambient conditions -- but the principle should be applicable for high-temperature use as well.

The process works because when the liquid freezes, the pressure of its forming crystal structure pushes the floating particles into closer contact, increasing their electrical and thermal conductance. When it melts, that pressure is relieved and the conductivity goes down. In their experiments, the researchers used a suspension that contained just 0.2 percent graphite flakes by volume. Such suspensions are remarkably stable: Particles remain suspended indefinitely in the liquid, as was shown by examining a container of the mixture three months after mixing.

By selecting different fluids and different materials suspended within that liquid, the critical temperature at which the change takes place can be adjusted at will, Chen says.

"Using phase change to control the conductivity of nanocomposites is a very clever idea," says Li Shi, a professor of mechanical engineering at the University of Texas at Austin. Shi adds that as far as he knows "this is the first report of this novel approach" to producing such a reversible system.

"I think this is a very crucial result," says Joseph Heremans, professor of physics and of mechanical and aerospace engineering at Ohio State University. "Heat switches exist," but involve separate parts made of different materials, whereas "here we have a system with no macroscopic moving parts," he says. "This is excellent work."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Massachusetts Institute of Technology. The original article was written by David L. Chandler, MIT News Office.

Journal Reference:

Ruiting Zheng, Jinwei Gao, Jianjian Wang, Gang Chen. Reversible temperature regulation of electrical and thermal conductivity using liquid–solid phase transitions. Nature Communications, 2011; 2: 289 DOI: 10.1038/ncomms1288

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New way to control conductivity: Reversible control of electrical and thermal properties could find uses in storage systems

ScienceDaily (May 5, 2011) — A team of researchers at MIT has found a way to manipulate both the thermal conductivity and the electrical conductivity of materials simply by changing the external conditions, such as the surrounding temperature. And the technique they found can change electrical conductivity by factors of well over 100, and heat conductivity by more than threefold.

"It's a new way of changing and controlling the properties" of materials -- in this case a class called percolated composite materials -- by controlling their temperature, says Gang Chen, MIT's Carl Richard Soderberg Professor of Power Engineering and director of the Pappalardo Micro and Nano Engineering Laboratories. Chen is the senior author of a paper describing the process that was published online on April 19 and will appear in a forthcoming issue of Nature Communications. The paper's lead authors are former MIT visiting scholars Ruiting Zheng of Beijing Normal University and Jinwei Gao of South China Normal University, along with current MIT graduate student Jianjian Wang. The research was partly supported by grants from the National Science Foundation.

The system Chen and his colleagues developed could be applied to many different materials for either thermal or electrical applications. The finding is so novel, Chen says, that the researchers hope some of their peers will respond with an immediate, "I have a use for that!"

One potential use of the new system, Chen explains, is for a fuse to protect electronic circuitry. In that application, the material would conduct electricity with little resistance under normal, room-temperature conditions. But if the circuit begins to heat up, that heat would increase the material's resistance, until at some threshold temperature it essentially blocks the flow, acting like a blown fuse. But then, instead of needing to be reset, as the circuit cools down the resistance decreases and the circuit automatically resumes its function.

Another possible application is for storing heat, such as from a solar thermal collector system, later using it to heat water or homes or to generate electricity. The system's much-improved thermal conductivity in the solid state helps it transfer heat.

Essentially, what the researchers did was suspend tiny flakes of one material in a liquid that, like water, forms crystals as it solidifies. For their initial experiments, they used flakes of graphite suspended in liquid hexadecane, but they showed the generality of their process by demonstrating the control of conductivity in other combinations of materials as well. The liquid used in this research has a melting point close to room temperature -- advantageous for operations near ambient conditions -- but the principle should be applicable for high-temperature use as well.

The process works because when the liquid freezes, the pressure of its forming crystal structure pushes the floating particles into closer contact, increasing their electrical and thermal conductance. When it melts, that pressure is relieved and the conductivity goes down. In their experiments, the researchers used a suspension that contained just 0.2 percent graphite flakes by volume. Such suspensions are remarkably stable: Particles remain suspended indefinitely in the liquid, as was shown by examining a container of the mixture three months after mixing.

By selecting different fluids and different materials suspended within that liquid, the critical temperature at which the change takes place can be adjusted at will, Chen says.

"Using phase change to control the conductivity of nanocomposites is a very clever idea," says Li Shi, a professor of mechanical engineering at the University of Texas at Austin. Shi adds that as far as he knows "this is the first report of this novel approach" to producing such a reversible system.

"I think this is a very crucial result," says Joseph Heremans, professor of physics and of mechanical and aerospace engineering at Ohio State University. "Heat switches exist," but involve separate parts made of different materials, whereas "here we have a system with no macroscopic moving parts," he says. "This is excellent work."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Massachusetts Institute of Technology. The original article was written by David L. Chandler, MIT News Office.

Journal Reference:

Ruiting Zheng, Jinwei Gao, Jianjian Wang, Gang Chen. Reversible temperature regulation of electrical and thermal conductivity using liquid–solid phase transitions. Nature Communications, 2011; 2: 289 DOI: 10.1038/ncomms1288

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New properties of supercooled confined water discovered

ScienceDaily (May 12, 2011) — A study led by the UB researcher Giancarlo Franzese and published in the journal Physical Review Letters suggests that hydrophobic nanoconfinement can alter the thermodynamics of water at supercool temperatures. These findings may have important applications in fields related to conservation at cryogenic temperatures (around -100 ºC) -- for example, in the preservation of stem cells, blood and food products.

The team behind the study, led by Giancarlo Franzese from the UB's Department of Fundamental Physics, included researchers from Boston University and TU Berlin.

Water exhibits atypical fluid behaviour. One of its unique characteristics is the increase in heat capacity as water cools, an anomaly that enables us to regulate our body temperature. When water is supercooled -- that is, when it is in liquid state at a temperature below its melting point -- the range of anomalies expands. This irregular behaviour has generated fierce scientific debate over the last twenty years and could hold the key to understanding why water is so different to other liquids and why it is so important for biological organisms.

From a technical perspective, it is difficult to observe supercooled water directly and many researchers opt to use nanoconfinement. In this study, the team used Monte Carlo simulations to study a layer of water only one nanometre high -- approximately equivalent to the diameter of three water molecules -- confined between two hydrophobic plates. Hydrophobic nanoparticles were then added to the water layer in random positions to generate nanochannels or variable size.

This process led to a strong decrease in thermodynamic fluctuations, reflected in compressibility, thermal expansion coefficient and specific heat. The observed decrease occurred at all pressures tested, and at pressures in the region of 180 MPa fluctuations dropped by almost 99% for a concentration in nanoparticles of 25% by volume. The reduction was found to be as high as 90% even at a particle concentration ten times lower.

According to Giancarlo Franzese, the results show that the thermodynamic behaviour of water confined in hydrophobic nanochannels is very different to that of unconfined water, even allowing for the possible presence of more than one liquid phase within the range of temperatures and pressures tested.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Universidad de Barcelona, via AlphaGalileo.

Journal Reference:

Elena Strekalova, Marco Mazza, H. Stanley, Giancarlo Franzese. Large Decrease of Fluctuations for Supercooled Water in Hydrophobic Nanoconfinement. Physical Review Letters, 2011; 106 (14) DOI: 10.1103/PhysRevLett.106.145701

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here