'Watermark ink' device identifies unknown liquids instantly

 Materials scientists and applied physicists collaborating at Harvard's School of Engineering and Applied Sciences (SEAS) have invented a new device that can instantly identify an unknown liquid.

The device, which fits in the palm of a hand and requires no power source, exploits the chemical and optical properties of precisely nanostructured materials to distinguish liquids by their surface tension.

The finding, published in the Journal of the American Chemical Society (JACS), offers a cheap, fast, and portable way to perform quality control tests anddiagnose liquid contaminants in the field.

"Digital encryption and sensors have become extremely sophisticated these days, but this is a tool that will work anywhere, without extra equipment, and with a verywide range of potential applications," says co-principal investigator Marko Lončar, Associate Professor of Electrical Engineering at SEAS.

Akin to the litmus paper used in chemistry labs around the world to detect the pH of a liquid, the new device changes color when it encounters a liquid with a particular surface tension. A single chip can react differently to a wide range of substances; it is also sensitive enough to distinguish between two very closely related liquids.

A hidden message can actually be "written" on a chip, revealing itself only when exposed to exactly the right substance. Dipped in another substance, the chip can display a different message altogether.

"This highly selective wetting would be very difficult to achieve on a two-dimensional surface," explains lead author Ian B. Burgess, a doctoral candidate in Lončar's lab and in the Aizenberg Biomineralization and Biomimetics Lab. "The optical and fluidic properties we exploit here are unique to the 3D nanostructure of the material."

The "Watermark Ink," or "W-Ink," concept relies on a precisely fabricated material called an inverse opal. The inverse opal is a layered glass structure with an internal network of ordered, interconnected air pores.

Co-authors Lidiya Mishchenko (a graduate student at SEAS) and Benjamin D. Hatton (a research appointee at SEAS and a technology development fellow at the Wyss Institute for Biologically Inspired Engineering at Harvard), recently perfected the production process of large-scale, highly ordered inverse opals.

"Two factors determine whether the color changes upon the introduction of a liquid: the surface chemistry and the degree of order in the pore structure," says Mishchenko, who works in the Aizenberg lab. "The more ordered the structure, the more control you can have over whether or not the liquid enters certain pores by just changing their surface chemistry."

Burgess and his colleagues discovered that selectively treating parts of the inverse opal with vaporized chemicals and oxygen plasma creates variations in the reactive properties of the pores and channels, letting certain liquids passthrough while excluding others.

Allowing liquid into a pore changes the material's optical properties, so the natural color of the inverse opal shows up only in the dry regions.

Each chip is calibrated to recognize only certain liquids, but it can be used over and over (provided the liquid evaporates between tests).

With the hope of commercializing the W-Ink technology, the researchers are currently developing more precisely calibrated chips and conducting field tests with government partners for applications in quality assurance and contaminant identification.

"If you want to detect forgeries," says Burgess, "you can tune your sensor to be acutely sensitive to one specific formulation, and then anything that's different stands out, regardless of the composition."

One immediate application would allow authorities to verify the fuel grade of gasoline right at the pump. Burgess also envisions creating a chip that tests bootleg liquor for toxic levels of methanol.

The W-Ink technology would additionally be useful for identifying chemical spills very quickly. A W-Ink chip that was calibrated to recognize a range of toxic substances could be used to determine, on the spot, whether the spill required special treatment.

"A device like this is not going to rival the selectivity of GC-MS [gas chromatography-mass spectrometry]," remarks co-principal investigatorJoanna Aizenberg, the Amy Smith Berylson Professor of Materials Science at SEAS and a core faculty member of the Wyss Institute.

"But the point is that if you want something in the field that requires no power, is easy to use, and gives you an instant result, then the W-Ink may be what you need."

Aizenberg is also the Susan S. and Kenneth L. Wallach Professor at the Radcliffe Institute for Advanced Study; Professor of Chemistry and Chemical Biology at Harvard; and Co-Director of the Kavli Institute for Bionano Science and Technology at Harvard.

Burgess, Mishchenko, Hatton, Lončar, and Aizenberg were joined on the paper by co-author Mathias Kolle, a postdoctoral researcher in Aizenberg's lab.

The "W-Ink" research was supported by grants from: the Air Force Office of Scientific Research; the Natural Sciences and Engineering Research Council of Canada; and the U.S. Department of Homeland Security (DHS), administered by the Oak Ridge Institute for Science and Education, through an interagency agreement between the U.S. Department of Energy and DHS.

Electron microscopy was performed at Harvard's Center for Nanoscale Systems, part of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation.

Story Source:

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

Journal Reference:

Ian B. Burgess, Lidiya Mishchenko, Benjamin D. Hatton, Mathias Kolle, Marko Loncˇar, Joanna Aizenberg. Encoding Complex Wettability Patterns in Chemically Functionalized 3D Photonic Crystals. Journal of the American Chemical Society, 2011; : 110726082238031 DOI: 10.1021/ja2053013

Discovery points way to graphene circuits: Materials scientists find new way to control electronic properties of graphene 'alloys'

Rice University materials scientists have made a fundamental discovery that could make it easier for engineers to build electronic circuits out of the much-touted nanomaterial graphene.

Graphene's stock shot sky-high last year when the nanomaterial attracted the Nobel Prize in physics. Graphene is a layer of carbon atoms that is just one atom thick. When stacked atop one another, graphene sheets form graphite, the material found in pencils the world over. Thanks to the tools of nanotechnology, scientists today can make, manipulate and study graphene with ease. Its unique properties make it ideal for creating faster, more energy-efficient computers and other nanoelectronic devices.

But there are hurdles. To make tiny circuits out of graphene, engineers need to find ways to create intricate patterns of graphene that are separated by a similarly thin nonconductive material. One possible solution is "white graphene," one-atom-thick sheets of boron and nitrogen that are physically similar to graphene but are electrically nonconductive.

In a new paper in the journal Nano Letters, Rice materials scientist Boris Yakobson and colleagues describe a discovery that could make it possible for nanoelectronic designers to use well-understood chemical procedures to precisely control the electronic properties of "alloys" that contain both white and black graphene.

"We found there was a direct relationship between the useful properties of the final product and the chemical conditions that exist while it is being made," Yakobson said. "If more boron is available during chemical synthesis, that leads to alloys with a certain type of geometric arrangement of atoms. The beauty of the finding is that we can precisely predict the electronic properties of the final product based solely upon the conditions -- technically speaking, the so-called 'chemical potential' -- during synthesis."

Yakobson said it took about one year for him and his students to understand exactly the distribution of energy transferred between each atom of carbon, boron and nitrogen during the formation of the "alloys." This precise level of understanding of the "bonding energies" between atoms, and how it is assigned to particular edges and interfaces, was vital to developing a direct link from synthesis to morphology and to useful product.

With interest in graphene running high, Yakobson said, the new study has garnered attention far and wide. Graduate student Yuanyue Liu, the study's lead co-author, is part of a five-student delegation that just returned from a weeklong visit to Tsinghua University in Beijing. Yakobson said the visit was part of an ongoing collaboration between Tsinghua researchers and colleagues in Rice's George R. Brown School of Engineering.

Rice postdoctoral fellow Somnath Bhowmick also co-authored the paper. The research was funded by the Department of Energy and the Office of Naval Research, and the computational resources were supported by the National Institute for Computational Sciences and the National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Rice University.

Journal Reference:

Yuanyue Liu, Somnath Bhowmick, Boris I. Yakobson. BN White Graphene with “Colorful” Edges: The Energies and Morphology. Nano Letters, 2011; 110714092023006 DOI: 10.1021/nl2011142

Scientists pioneer new method for nanoribbon production

Research involving scientists from The University of Nottingham is pioneering a new method of studying and making molecules.

The work, reported in Nature Materials, could pave the way for the production of nanomaterials for use in a new generation of computers and data storage devices that are faster, smaller and more powerful.

The Nottingham research group, led by Dr Andrei Khlobystov in the University's School of Chemistry, specialise in the chemistry of nanomaterials and has been studying carbon nanotubes as containers for molecules and atoms.

Carbon nanotubes are remarkable nanostructures with a typical diameter of 1-2 nanometres, which is 80,000 times smaller than the thickness of a human hair. Over the past few years, the researchers have discovered that physical and chemical properties of molecules inserted into carbon nanotubes are very different to the properties of free molecules. This presents a powerful mechanism for manipulating the molecules, harnessing their functional properties, such as magnetic or optical, and for controlling their chemical reactivity.

The latest study is a collaboration between Dr Khlobystov's chemical nanoscientists, theoretical chemists based in the University's School of Chemistry and electron microscopists from Ulm University in German.

Working together, they have demonstrated that carbon nanotubes can be used as nanoscale chemical reactors and chemical reactions involving carbon and sulphur atoms held within a nanotube lead to the formation of atomically thin strips of carbon, known as graphene nanoribbon, decorated with sulphur atoms around the edge.

Dr Khlobystov said: "Graphene nanoribbons possess a wealth of interesting physical properties making them more suitable for applications in electronic and spintronic devices than the parent material graphene -- the discovery of which attracted the Nobel Prize for Physics last year for University of Manchester scientists Professors Andre Geim and Konstantin Novoselov.

"Nanoribbons are very difficult to make but the Nottingham team's strategy of confining chemical reactions at the nanoscale sparks spontaneous formation of these remarkable structures. The team has also discovered that nanoribbons -- far from being simple flat and linear structures -- possess an unprecedented helical twist that changes over time, giving scientists a way of controlling physical properties of the nanoribbon, such as electrical conductivity."

Devices based on nanoribbons could potentially be used as nano-switches, nano-actuators and nano-transistors integrated in computers or data storage devices.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Nottingham.

Journal Reference:

A. Chuvilin, E. Bichoutskaia, M. C. Gimenez-Lopez, T. W. Chamberlain, G. A. Rance, N. Kuganathan, J. Biskupek, U. Kaiser, A. N. Khlobystov. Self-assembly of a sulphur-terminated graphene nanoribbon within a single-walled carbon nanotube. Nature Materials, 2011; DOI: 10.1038/nmat3082

Better desalination technology key to solving world's water shortage

Over one-third of the world's population already lives in areas struggling to keep up with the demand for fresh water. By 2025, that number will nearly double. Some countries have met the challenge by tapping into natural sources of fresh water, but as many examples -- such as the much-depleted Jordan River -- have demonstrated, many of these practices are far from sustainable.

A new Yale University study argues that seawater desalination should play an important role in helping combat worldwide fresh water shortages -- once conservation, reuse and other methods have been exhausted -- and provides insight into how desalination technology can be made more affordable and energy efficient.

"The globe's oceans are a virtually inexhaustible source of water, but the process of removing its salt is expensive and energy intensive," said Menachem Elimelech, a professor of chemical and environmental engineering at Yale and lead author of the study, which appears in the Aug. 5 issue of the journal Science.

Reverse osmosis -- forcing seawater through a membrane that filters out the salt -- is the leading method for seawater desalination in the world today. For years, scientists have focused on increasing the membrane's water flux using novel materials, such as carbon nanotubes, to reduce the amount of energy required to push water through it.

In the new study, Elimelech and William Phillip, now at the University of Notre Dame, demonstrate that reverse osmosis requires a minimum amount of energy that cannot be overcome, and that current technology is already starting to approach that limit. Instead of higher water flux membranes, Elimelech and Phillip suggest that the real gains in efficiency can be made during the pre- and post-treatment stages of desalination.

Seawater contains naturally occurring organic and particulate matter that must be filtered out before it passes through the membrane that removes the salt. Chemical agents are added to the water to clean it and help coagulate this matter for easier removal during a pre-treatment stage. But if a membrane didn't build up organic matter on its surface, most if not all pre-treatment could be avoided, according to the scientist's findings.

In addition, Elimelech and Phillip calculate that a membrane capable of filtering out boron and chloride would result in substantial energy and cost savings. Seventy percent of the world's water is used in agriculture, but water containing even low levels of boron and chloride -- minerals that naturally occur in seawater -- cannot be used for these purposes. Instead of removing them during a separate post-treatment stage, the scientists believe a membrane could be developed that would filter them more efficiently at the same time as the salt is removed.

Elimelech cautions that desalination should only be considered a last resort in the effort to provide fresh water to the world's populations and suggests that long-term research is needed to determine the impact of seawater desalination on the aquatic environment, but believes that desalination has a major role to play now and in the future.

"All of this will require new materials and new chemistry, but we believe this is where we should focus our efforts going forward," Elimelech said. "The problem of water shortage is only going to get worse, and we need to be ready to meet the challenge with improved, sustainable technology."

Story Source:

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

Journal Reference:

Menachem Elimelech, William A. Phillip. The Future of Seawater Desalination: Energy, Technology, and the Environment. Science, 5 August 2011: Vol. 333 no. 6043 pp. 712-717 DOI: 10.1126/science.1200488