Tuesday, March 13, 2012

New measuring techniques can improve efficiency, safety of nanoparticles

Using high-precision microscopy and X-ray scattering techniques, University of Oregon researchers have gained eye-opening insights into the process of applying green chemistry to nanotechnology that results in high yields, improves efficiency and dramatically reduces waste and potential negative exposure to human health or the environment.

University of Oregon chemist James E. Hutchison described his lab's recent efforts to monitor the dynamics of nanoparticles in an invited talk Feb. 28 at the American Physical Society's March Meeting (Feb. 27-March 2) in Boston, Mass. It turns out, Hutchison said, that simply reducing the amount of gold -- the material used in his research -- in the initial stages of the process used to grow nanoparticles allows for better maintenance of the particle size.

That accomplishment, he said, has important implications. The use of lower concentrations of the precursor that forms the nanoparticles virtually eliminates the ability of nanoparticles to aggregate together and thus prevents variations of sizes of the desired end product.

"What we saw while observing the production process with small-angle X-ray scattering (SAXS) was amazing," Hutchison, said in an interview before his lecture. "We realized that it is possible to reduce the concentration of gold and allow the particles to still grow, but shutdown the coalescent, or aggregation, pathway."

He also summarized his lab's use of chemically modified grids (Smart Grids) in transmission electron microscopy to study how nanoparticles are shed from common objects such as silverware and copper jewelry -- findings that were detailed in the journal ACS Nano in October. They studied the transformation of silver nanoparticles coated on Smart Grids as well as the common objects and found that all forms produce smaller silver nanoparticles that could disperse into the environment, especially in humid air, water and light -- and likely have been doing that throughout time without any known health ramifications.

"There may be many beneficial applications to nanotechnology, but they are only beneficial if the net benefits outweigh the deleterious implications for human health and the environment," said Hutchison, who holds the Lokey-Harrington Chair in Chemistry at the University of Oregon.

These new monitoring and measuring techniques, he said, are vital to help understand what modifications are possible in the processes that grow nanoparticles for a desired product. Using green chemistry, he added, can help assure both efficiency and stability of a product, which, in turn, will lower the risk of unwanted environmental or harmful human-health consequences.

"Advancing the safe implementation of nanotechnology is vital to many fields, from electronics to medicine and materials science, in general," said Kimberly Andrews Espy, vice president for research and innovation at the UO. "Professor Hutchison has been a leader in the University of Oregon's efforts to promote green chemistry in this effort, and his work continues to set examples on how best to use it."

Hutchison is co-author of "Green Nanotechnology Challenges and Opportunities," a white paper published by the American Chemical Society's Green Chemistry Institute, and the National Research Council report, "A Research Strategy for Environmental, Health, and Safety Aspects of Engineered Nanomaterials." He also was the founding director of the Safer Nanomaterials and Nanomanufacturing Initiative (SSNI) of the Oregon Nanoscience and Microtechnologies Institute (ONAMI), a state signature research center.

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The above story is reprinted from materials provided by University of Oregon.

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Liquid water diffusion at molecular level

ScienceDaily (Feb. 24, 2012) — Researchers at the universities of Granada and Barcelona have described for the first time the diffusion of liquid water through nanochannels in molecular terms; nanochannels are extremely tiny channels with a diameter of 1-100 nanometers that scientists use to study the behavior of molecules (nm. a unit of length in the metric system equal to one billionth of a meter that is used in the field of nanotechnology).

This study might have an important impact on water desalinization and filtration methods. Two articles published in Science state that the introduction of graphene membranes and carbon nanolayers will revolutionize water desalinization and filtration processes, as water diffuses rapidly through these materials when their pores are 1nm in diameter.

Liquid water exhibits a range of unusual properties that other chemical compounds do not have: up to 65 abnormalities. Some of these abnormalities have been known for 300 years, such as the fact that water expands below 4oC.

Many of the abnormalities found in water have a dynamic nature -- e.g. water molecules move faster as density increases -- as a result of the properties of the hydrogen bond networks that form between water molecules; hydrogen bonds lead to the formation of tetrahedral structures wherein a central atom is located at the center with four molecules located at the corners. However, this geometrical structure changes with pressure and temperature and, until now, changes in the molecular structure and properties of liquid water had not been described.

A Mystery to Solve

Particularly confusing are the results on the diffusion of water confined between two hydrophobic plates. Neither experiments nor computer-based models have clarified whether confinement increases or reduces the mobility of water molecules. However, it seems that the mobility of water molecules relies on ducts having a diameter above or below 1nm.

In a study published in the journal Physical Review, professors Francisco de los Santos Fernández (University of Granada) and Giancarlo Franzese (University of Barcelona) described the behavior of water confined between two hydrophobic plates. In their study, Franzese and Fernandez used models to demonstrate that the diffusion of nanoconfined water is unusually fast, as a result of the competition between the formation and breaking of hydrogen bonds, and the free volume available for cooperative molecule rearrangement.

In nanochannels above 1 nm in diameter, macroscopic diffusion of water only occurs if there is a cooperative rearrangement of molecules, which leads to HB breaking within a cooperative region of 1nm in size. On the other hand, diffusion increases in nanochannels below 1 nm, as fewer HBs need to be broken. Thus, this study proves that the interplay between hydrogen bond breaking and cooperative rearranging within regions of 1-nm determine the macroscopic properties of water.

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The above story is reprinted from materials provided by University of Granada, via AlphaGalileo.

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Journal Reference:

Francisco de los Santos, Giancarlo Franzese. Relations between the diffusion anomaly and cooperative rearranging regions in a hydrophobically nanoconfined water monolayer. Physical Review E, 2012; 85 (1) DOI: 10.1103/PhysRevE.85.010602

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How heavy and light isotopes separate in magma

 In the crash-car derby between heavy and light isotopes vying for the coolest spots as magma turns to solid rock, weightier isotopes have an edge, research led by Case Western Reserve University shows.

This tiny detail may offer clues to how igneous rocks form.

As molten rock cools along a gradient, atoms want to move towards the cool end. This happens because hotter atoms move faster than cooler atoms and, therefore, hotter atoms move to the cool region faster than the cooler atoms move to the hot region.

Although all isotopes of the same element want to move towards the cool end, the big boys have more mass and, therefore, momentum, enabling them to keep moving on when they collide along the way.

"It's as if you have a crowded, sealed room of sumo wrestlers and geologists and a fire breaks out at one side of the room," said Daniel Lacks, chemical engineering professor and lead author of the paper. "All will try to move to the cooler side of the room, but the sumo wrestlers are able to push their way through and take up space on the cool side, leaving the geologists on the hot side of the room."

Lacks worked with former postdoctoral researcher Gaurav Goel and geology professor James A. Van Orman at Case Western Reserve; Charles J. Bopp IV and Craig C. Lundstrum, of University of Illinois, Urbana; and Charles E. Lesher of the University of California at Davis. They described their theory and confirming mathematics, computer modeling, and experiments in the current issue of Physical Review Letters.

Lacks, Van Orman and Lesher also published a short piece in the current issue of Nature, showing how their findings overturn an explanation based on quantum mechanics, published in that journal last year.

"The theoretical understanding of thermal isotope separation in gases was developed almost exactly 100 years ago by David Enskog, but there is as yet not a similar full understanding of this process in liquids," said Frank Richter, who is the Sewell Avery Distinguished Professor at the University of Chicago and a member of the National Academy of Sciences. He was not involved in the research. "This work by Lacks et al. is an important step towards remedying this situation."

This separation among isotopes of the same element is called fractionation.

Scientists have been able to see fractionation of heavy elements in igneous rocks only since the 1990s, Van Orman said. More sensitive mass spectrometers showed that instead of a homogenous distribution, the concentration ratio of heavy isotopes to light isotopes in some igneous rocks was up to 0.1 percent higher than in other rocks.

One way of producing this fractionation is by temperature.

To understand how this happens, the team of researchers created a series of samples made of molten magnesium silicate infused with elements of different mass, from oxygen on up to heavy uranium.

The samples, called silicate melts, were heated at one end in a standard lab furnace, creating temperature gradients in each. The melts were then allowed to cool and solidify.

The scientists then sliced the samples along gradient lines and dissolved the slices in acid. Analysis showed that no matter the element, the heavier isotopes slightly outnumbered the lighter at the cool end of the gradient.

Computer simulations of the atoms, using classical mechanics, agreed with the experimental results.

"The process depends on temperature differences and can be seen whether the temperature change across the sample is rapid or gradual," Lacks said.

Thermal diffusion through gases was one of the first methods used to separate isotopes, during the Manhattan Project. It turns out that isotope fractionation through silicate liquids is even more efficient than through gases.

"Fractionation can occur inside the Earth wherever a sustained temperature gradient exists," Van Orman said. "One place this might happen is at the margin of a magma chamber, where hot magma rests against cold rock. Another is nearly 1,800 miles inside the Earth, at the boundary of the liquid core and the silicate mantle."

The researchers are now adding pressure to the variables as they investigate further. This work was done at atmospheric pressure but where Earth's core and mantle meet, the pressure is nearly 1.4 million atmospheres.

Lacks and Van Orman are unsure whether high pressure will result in greater or lesser fractionation. They can see arguments in favor of either.

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The above story is reprinted from materials provided by Case Western Reserve University.

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Journal Reference:

Daniel Lacks, Gaurav Goel, Charles Bopp, James Van Orman, Charles Lesher, Craig Lundstrom. Isotope Fractionation by Thermal Diffusion in Silicate Melts. Physical Review Letters, 2012; 108 (6) DOI: 10.1103/PhysRevLett.108.065901

Researchers capture first-ever image of two atoms forming a molecule

 Researchers have recorded the first-ever image of two atoms bonding together to form a molecule.

Key to the experiment, which appears in the journal Nature, is the researchers' use of the energy of a single electron as a kind of "flash bulb" to illuminate the reaction.

The team used ultrafast laser pulses to knock one electron out of its natural orbit in one of the atoms, just as the two atoms were bonding together. When the electron fell back into place, it emitted an energy signal that scattered around the newly forming molecule as a flash of light would scatter around an object, or ripples would scatter in a pond.

Principal investigator Louis DiMauro of Ohio State University said that the feat marks a first step toward not only observing chemical reactions, but also controlling them on an atomic scale.

"Through these experiments, we realized that we can control the trajectory of the electron when it comes back to the molecule, by adjusting the orientation of the laser that launches it," said DiMauro, who is a professor of physics at Ohio State. "The next step will be to see if we can hit the electron in just the right way to actually control a chemical reaction."

A more common imaging technique involves shooting a molecule with an electron beam, bombarding it with millions of electrons per second. The researchers deemed the new single-electron approach more reliable, based on theoretical developments by the paper's coauthors at Kansas State University.

"If we shot an electron beam from outside the molecule, there would only be a certain probability that one of the electrons would scatter off the molecule," explained Ohio State postdoctoral researcher Cosmin Blaga. "But in this case, when we use a laser to launch an electron from inside the molecule we are studying, we have a 100 percent probability that it will fall back into the molecule and scatter."

The technique, called laser induced electron diffraction (LIED), is commonly used in surface science to study solid materials. This is the first time anyone has used LIED to study a single molecule as it formed.

The molecules the researchers chose to study were simple ones: they brought two nitrogen atoms together to form molecular nitrogen, or N2, then repeated the experiment with two oxygen atoms forming molecular oxygen, or O2. N2 and O2 are common atmospheric gases, and scientists already know every detail of how they form, so these two very basic reactions made good test cases for the LIED technique.

In each case, the researchers hit the forming molecule with laser light pulses of 50 femtoseconds, or quadrillionths of a second. They were able to knock a single electron out of the outer shell of one of the constituent atoms and detect the energy signal of the electron as it fell back into the molecule.

DiMauro and Blaga likened the electron signal to the diffraction pattern that light forms when it passes through slits. Given only the diffraction pattern, scientists can reconstruct the size and shape of the slits. In this case, given the diffraction pattern of the electron, the physicists reconstructed the size and shape of the molecule -- that is, the locations of the constituent atoms' nuclei and the electron shells orbiting them.

The resulting 3D image marks the first image ever recorded of bonds forming in a molecule.

Beyond its potential for controlling chemical reactions, the technique offers a new tool to study the structure and dynamics of matter, Blaga said. "Ultimately, we want to really understand how chemical reactions take place. So, long-term, there would be applications in materials science and even chemical manufacture."

"You could use this to study individual atoms," DiMauro added, "but it's safe to say that we won't learn anything new from an atomic physics standpoint. The greater impact to science will come when we can study reactions between more complex molecules. Looking at two atoms -- that's a long way from studying a more interesting molecule like a protein."

Coauthors on the paper included Anthony DiChiara, Emily Sistrunk, Kaikai Zhang, Pierre Agostini, and Terry A. Miller of Ohio State; and C.D. Lin of Kansas State. Coauthor Junliang Xu pursued the theoretical side of this research to earn his doctorate at Kansas State, and will soon join DiMauro's lab as a postdoctoral researcher.

Funding came from the U.S. Department of Energy Basic Energy Sciences Program.

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The above story is reprinted from materials provided by Ohio State University, via Newswise.

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Journal Reference:

Cosmin I. Blaga, Junliang Xu, Anthony D. DiChiara, Emily Sistrunk, Kaikai Zhang, Pierre Agostini, Terry A. Miller, Louis F. DiMauro, C. D. Lin. Imaging ultrafast molecular dynamics with laser-induced electron diffraction. Nature, 2012; 483 (7388): 194 DOI: 10.1038/nature10820