World's smallest steam engine: Heat engine measuring only a few micrometers works as well as its larger counterpart, although it sputters

 What would be a case for the repair shop for a car engine is completely normal for a micro engine. If it sputters, this is caused by the thermal motions of the smallest particles, which interfere with its running. Researchers at the University of Stuttgart and the Stuttgart-based Max Planck Institute for Intelligent Systems have now observed this with a heat engine on the micrometre scale. They have also determined that the machine does actually perform work, all things considered. Although this cannot be used as yet, the experiment carried out by the researchers in Stuttgart shows that an engine does basically work, even if it is on the microscale. This means that there is nothing, in principle, to prevent the construction of highly efficient, small heat engines.

A technology which works on a large scale can cause unexpected problems on a small one. And these can be of a fundamental nature. This is because different laws prevail in the micro- and the macroworld. Despite the different laws, some physical processes are surprisingly similar on both large and small scales. Clemens Bechinger, Professor at the University of Stuttgart and Fellow of the Max Planck Institute for Intelligent Systems, and his colleague Valentin Blickle have now observed one of these similarities.

"We've developed the world's smallest steam engine, or to be more precise the smallest Stirling engine, and found that the machine really does perform work," says Clemens Bechinger. "This was not necessarily to be expected, because the machine is so small that its motion is hindered by microscopic processes which are of no consequence in the macroworld." The disturbances cause the micromachine to run rough and, in a sense, sputter.

The laws of the microworld dictated that the researchers were not able to construct the tiny engine according to the blueprint of a normal-sized one. In the heat engine invented almost 200 years ago by Robert Stirling, a gas-filled cylinder is periodically heated and cooled so that the gas expands and contracts. This makes a piston execute a motion with which it can drive a wheel, for example.

"We successfully decreased the size of the essential parts of a heat engine, such as the working gas and piston, to only a few micrometres and then assembled them to a machine," says Valentin Blickle. The working gas in the Stuttgart-based experiment thus no longer consists of countless molecules, but of only one individual plastic bead measuring a mere three micrometres (one micrometre corresponds to one thousandth of a millimetre) which floats in water. Since the colloid particle is around 10,000 times larger than an atom, researchers can observe its motion directly in a microscope.

The physicists replaced the piston, which moves periodically up and down in a cylinder, by a focused laser beam whose intensity is periodically varied. The optical forces of the laser limit the motion of the plastic particle to a greater and a lesser degree, like the compression and expansion of the gas in the cylinder of a large heat engine. The particle then does work on the optical laser field. In order for the contributions to the work not to cancel each other out during compression and expansion, these must take place at different temperatures. This is done by heating the system from the outside during the expansion process, just like the boiler of a steam engine. The researchers replaced the coal fire of an old-fashioned steam engine with a further laser beam that heats the water suddenly, but also lets it cool down as soon as it is switched off.

The fact that the Stuttgart machine runs rough is down to the water molecules which surround the plastic bead. The water molecules are in constant motion due to their temperature and continually collide with the microparticle. In these random collisions, the plastic particle constantly exchanges energy with its surroundings on the same order of magnitude as the micromachine converts energy into work. "This effect means that the amount of energy gained varies greatly from cycle to cycle, and even brings the machine to a standstill in the extreme case," explains Valentin Blickle. Since macroscopic machines convert around 20 orders of magnitude more energy, the tiny collision energies of the smallest particles in them are not important.

The physicists are all the more astonished that the machine converts as much energy per cycle on average despite the varying power, and even runs with the same efficiency as its macroscopic counterpart under full load. "Our experiments provide us with an initial insight into the energy balance of a heat engine operating in microscopic dimensions. Although our machine does not provide any useful work as yet, there are no thermodynamic obstacles, in principle, which prohibit this in small dimensions," says Clemens Bechinger. This is surely good news for the design of reliable, highly efficient micromachines.

The above story is reprinted from materials provided by Max-Planck-Gesellschaft.

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Journal Reference:

Valentin Blickle and Clemens Bechinger. Realization of a micrometre-sized stochastic heat engine. Nature Physics, 11 December 2011 DOI: 10.1038/NPHYS2163

'Fool's gold' aids discovery of new options for cheap, benign solar energy

 Pyrite, better known as "fool's gold," was familiar to the ancient Romans and has fooled prospectors for centuries -- but has now helped researchers at Oregon State University discover related compounds that offer new, cheap and promising options for solar energy.

These new compounds, unlike some solar cell materials made from rare, expensive or toxic elements, would be benign and could be processed from some of the most abundant elements on Earth. Findings on them have been published in Advanced Energy Materials, a professional journal.

Iron pyrite itself has little value as a future solar energy compound, the scientists say, just as the brassy, yellow-toned mineral holds no value compared to the precious metal it resembles. But for more than 25 years it was known to have some desirable qualities that made it of interest for solar energy, and that spurred the recent research.

The results have been anything but foolish.

"We've known for a long time that pyrite was interesting for its solar properties, but that it didn't actually work," said Douglas Keszler, a distinguished professor of chemistry at OSU. "We didn't really know why, so we decided to take another look at it. In this process we've discovered some different materials that are similar to pyrite, with most of the advantages but none of the problems.

"There's still work to do in integrating these materials into actual solar cells," Keszler said. "But fundamentally, it's very promising. This is a completely new insight we got from studying fool's gold."

Pyrite was of interest early in the solar energy era because it had an enormous capacity to absorb solar energy, was abundant, and could be used in layers 2,000 times thinner than some of its competitors, such as silicon. However, it didn't effectively convert the solar energy into electricity.

In the new study, the researchers found out why. In the process of creating solar cells, which takes a substantial amount of heat, pyrite starts to decompose and forms products that prevent the creation of electricity.

Based on their new understanding of exactly what the problem was, the research team then sought and found compounds that had the same capabilities of pyrite but didn't decompose. One of them was iron silicon sulfide.

"Iron is about the cheapest element in the world to extract from nature, silicon is second, and sulfur is virtually free," Keszler said. "These compounds would be stable, safe, and would not decompose. There's nothing here that looks like a show-stopper in the creation of a new class of solar energy materials."

Work to continue the development of the materials and find even better ones in the same class will continue at the National Renewable Energy Laboratory in Colorado, which collaborated on this research.

The work was done at the Center for Inverse Design, a collaborative initiative of the College of Science and College of Engineering at OSU, formed two years ago with a $3 million grant from the U.S. Department of Energy. It was one of the new Energy Frontier Research Centers set up through a national, $777 million federal program to identify energy solutions for the future.

The OSU program is different from traditional science, in which the process often is to discover something and then look for a possible application. In this center, researchers start with an idea of what they want and then try to find the kind of materials, atomic structure or even construction methods it would take to achieve it.

Finding cheap, environmentally benign and more efficient materials for solar energy is necessary for the future growth of the industry, researchers said.

"The beauty of a material such as this is that it is abundant, would not cost much and might be able to produce high-efficiency solar cells," Keszler said. "That's just what we need for more broad use of solar energy."

Story Source:

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

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Liping Yu, Stephan Lany, Robert Kykyneshi, Vorranutch Jieratum, Ram Ravichandran, Brian Pelatt, Emmeline Altschul, Heather A. S. Platt, John F. Wager, Douglas A. Keszler, Alex Zunger. Iron Chalcogenide Photovoltaic Absorbers. Advanced Energy Materials, 2011; 1 (5): 748 DOI: 10.1002/aenm.201100351

'Label-free' imaging tool tracks nanotubes in cells, blood for biomedical research

 Researchers have demonstrated a new imaging tool for tracking structures called carbon nanotubes in living cells and the bloodstream, which could aid efforts to perfect their use in biomedical research and clinical medicine.

The structures have potential applications in drug delivery to treat diseases and imaging for cancer research. Two types of nanotubes are created in the manufacturing process, metallic and semiconducting. Until now, however, there has been no technique to see both types in living cells and the bloodstream, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.

The imaging technique, called transient absorption, uses a pulsing near-infrared laser to deposit energy into the nanotubes, which then are probed by a second near-infrared laser.

The researchers have overcome key obstacles in using the imaging technology, detecting and monitoring the nanotubes in live cells and laboratory mice, Cheng said.

"Because we can do this at high speed, we can see what's happening in real time as the nanotubes are circulating in the bloodstream," he said.

Findings are detailed in a research paper posted online Dec. 4 in the journal Nature Nanotechnology.

The imaging technique is "label free," meaning it does not require that the nanotubes be marked with dyes, making it potentially practical for research and medicine, Cheng said.

"It's a fundamental tool for research that will provide information for the scientific community to learn how to perfect the use of nanotubes for biomedical and clinical applications," he said.

The conventional imaging method uses luminescence, which is limited because it detects the semiconducting nanotubes but not the metallic ones.

The nanotubes have a diameter of about 1 nanometer, or roughly the length of 10 hydrogen atoms strung together, making them far too small to be seen with a conventional light microscope. One challenge in using the transient absorption imaging system for living cells was to eliminate the interference caused by the background glow of red blood cells, which is brighter than the nanotubes.

The researchers solved this problem by separating the signals from red blood cells and nanotubes in two separate "channels." Light from the red blood cells is slightly delayed compared to light emitted by the nanotubes. The two types of signals are "phase separated" by restricting them to different channels based on this delay.

Researchers used the technique to see nanotubes circulating in the blood vessels of mice earlobes.

"This is important for drug delivery because you want to know how long nanotubes remain in blood vessels after they are injected," Cheng said. "So you need to visualize them in real time circulating in the bloodstream."

The structures, called single-wall carbon nanotubes, are formed by rolling up a one-atom-thick layer of graphite called graphene. The nanotubes are inherently hydrophobic, so some of the nanotubes used in the study were coated with DNA to make them water-soluble, which is required for them to be transported in the bloodstream and into cells.

The researchers also have taken images of nanotubes in the liver and other organs to study their distribution in mice, and they are using the imaging technique to study other nanomaterials such as graphene.

The paper was written by doctoral student Ling Tong; postdoctoral research associate Yuxiang Liu; doctoral students Bridget D. Dolash and Yookyung Jung; biomedical engineering research scientist Mikhail N. Slipchenko; Donald E. Bergstrom, the Walther Professor of Medicinal Chemistry; and Cheng.

The research is funded by the National Science Foundation.

Story Source:

The above story is reprinted from materials provided by Purdue University. The original article was written by Emil Venere.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Ling Tong, Yuxiang Liu, Bridget D. Dolash, Yookyung Jung, Mikhail N. Slipchenko, Donald E. Bergstrom, Ji-Xin Cheng. Label-free imaging of semiconducting and metallic carbon nanotubes in cells and mice using transient absorption microscopy. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.210

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

New solar-powered classroom brings science to schools in developing countries

 An innovative project led by a chemistry academic at the University of Southampton is using solar generators to provide IT resources and 'hands-on' science for students in developing countries.

A major difficulty in teaching science subjects in developing countries, especially in rural schools, is that students are rarely able to get 'hands-on' experience of experiments. This could be partly due to a lack of equipment, chemicals and facilities but mainly because of a lack of electricity and running water.

Now, Professor Tony Rest, a visiting Chemistry academic at the University of Southampton, and Keith Wilkinson, formerly a teacher at the International School at Lusaka in Zambia, have devised a solar-powered solution based on a digital projector and low-cost solar energy panels so that students can gain access to IT and other modern teaching methods.

Professor Rest says: "The lack of electricity is a particularly serious matter for rural schools and this situation is unlikely to get better in the near to medium future. With drawbacks to petrol generators, due to difficulties in getting supplies and safety hazards, solar energy generators have become available at cost-effective prices and provide a sustainable answer as rural schools have an abundance of the basic energy source required to power them -- sunshine.

Most data/video projectors require 200-300 watt and cannot be economically sustained by solar power in rural villages. However, the advent of mini-projectors, which require about 50 watts of power, has revolutionised the situation and made battery powered projection feasible.

The solar energy generators, which consist of solar panels, batteries and inverters, can be linked to the projector for students to get practical classes via multimedia resources to show laboratory experiments and stress practical techniques.

Professor Rest adds: "These experiences can be extended to other science subjects from physics, biology and maths, to subjects involving practical elements, such as engineering, and to craft subjects, including plumbing, carpentry, and catering, where students need see how to acquire skills. By extending the breadth of subjects benefiting from the use of IT, the overall cost of using a solar energy generator is reduced. Another spin-off is that students in rural schools gain access to valuable IT skills."

The project has been developed by the 'Chemistry Aid' project, the Chemistry Video Consortium based at the University of Southampton, with support from the Royal Society of Chemistry, which has provided multimedia teaching resources.

Story Source:

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

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Chemists become molecular sculptors, synthesizing tiny, molecular traps

 Using clever but elegant design, University at Buffalo chemists have synthesized tiny, molecular cages that can be used to capture and purify nanomaterials.

Sculpted from a special kind of molecule called a "bottle-brush molecule," the traps consist of tiny, organic tubes whose interior walls carry a negative charge. This feature enables the tubes to selectively encapsulate only positively charged particles.

In addition, because UB scientists construct the tubes from scratch, they can create traps of different sizes that snare molecular prey of different sizes. The level of fine tuning possible is remarkable: In the Journal of the American Chemical Society, the researchers report that they were able to craft nanotubes that captured particles 2.8 nanometers in diameter, while leaving particles just 1.5 nanometers larger untouched.

These kinds of cages could be used, in the future, to expedite tedious tasks, such as segregating large quantum dots from small quantum dots, or separating proteins by size and charge.

"The shapes and sizes of molecules and nanomaterials dictate their utility for desired applications. Our molecular cages will allow one to separate particles and molecules with pre-determined dimensions, thus creating uniform building blocks for the fabrication of advanced materials," said Javid Rzayev, the UB assistant professor of chemistry who led the research.

"Just like a contractor wants tile squares or bricks to be the same size so they fit well together, scientists are eager to produce nanometer-size particles with the same dimensions, which can go a long way toward creating uniform and well-behaved materials," Rzayev said.

To create the traps, Rzayev and his team first constructed a special kind of molecule called a bottle-brush molecule. These resemble a round hair brush, with molecular "bristles" protruding all the way around a molecular backbone.

After stitching the bristles together, the researchers hollowed out the center of each bottle-brush molecule, leaving behind a structure shaped like a toilet paper tube.

The carving process employed simple but clever chemistry: When building their bottlebrush molecules, the scientists constructed the heart of each molecule using molecular structures that disintegrate upon coming into contact with water. Around this core, the scientists then attached a layer of negatively charged carboxylic acid groups.

To sculpt the molecule, the scientists then immersed it water, in effect hollowing the core. The resulting structure was the trap -- a nanotube whose inner walls were negatively charged due to the presence of the newly exposed carboxylic acid groups.

To test the tubes' effectiveness as traps, Rzayev and colleagues designed a series of experiments involving a two-layered chemical cocktail.

The cocktail's bottom layer consisted of a chloroform solution containing the nanotubes, while the top layer consisted of a water-based solution containing positively charged dyes. (As in a tequila sunrise, the thinner, water-based solution floats on top of the denser chloroform solution, with little mixing.)

When the scientists shook the cocktail for five minutes, the nanotubes collided with and trapped the dyes, bringing the dyes into the chloroform solution. (The dyes, on their own, do not dissolve in chloroform.)

In similar experiments, Rzayev and his team were able to use the nanotubes to extract positively charged molecules called dendrimers from an aqueous solution. The nanotubes were crafted so that dendrimers with a diameter of 2.8 nanometers were trapped, while dendrimers that were 4.3 nanometers across were left in solution.

To remove the captured dendrimers from the nanotubes, the researchers simply lowered the pH of the chloroform solution, which shuts down the negative charge inside the traps and allows the captured particles to be released from their cages.

The research on nanotubes is part of a larger suite of studies Rzayev is conducting on bottle-brush molecules using a National Science Foundation CAREER award. His other work includes the fabrication of bottle-brush-based nanomembranes that could be adapted for water filtration, and the assembly of layered, bottle-brush polymers that reflect visible light like the wings of a butterfly do.

Story Source:

The above story is reprinted from materials provided by University at Buffalo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Kun Huang, Javid Rzayev. Charge and Size Selective Molecular Transport by Amphiphilic Organic Nanotubes. Journal of the American Chemical Society, 2011; 133 (42): 16726 DOI: 10.1021/ja204296v

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