Engineers build world's smallest, fastest nanomotor: Can fit inside a single cell

Engineers build world's smallest, fastest nanomotor: Can fit inside a single cell

  7:47:00 PM    Science Lover

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Researchers at the Cockrell School of Engineering at The University of Texas at Austin have built the smallest, fastest and longest-running tiny synthetic motor to date. The team's nanomotor is an important step toward developing miniature machines that could one day move through the body to administer insulin for diabetics when needed, or target and treat cancer cells without harming good cells.

Simple nanomotor. Credit: Image courtesy of University of Texas at Austin

With the goal of powering these yet-to-be invented devices, UT Austin engineers focused on building a reliable, ultra-high-speed nanomotor that can convert electrical energy into mechanical motion on a scale 500 times smaller than a grain of salt.

Mechanical engineering assistant professor Donglei "Emma" Fan led a team of researchers in the successful design, assembly and testing of a high-performing nanomotor in a nonbiological setting. The team's three-part nanomotor can rapidly mix and pump biochemicals and move through liquids, which is important for future applications. The team's study was published in a recent issue of Nature Communications.

Fan and her team are the first to achieve the extremely difficult goal of designing a nanomotor with large driving power.

With all its dimensions under 1 micrometer in size, the nanomotor could fit inside a human cell and is capable of rotating for 15 continuous hours at a speed of 18,000 RPMs, the speed of a motor in a jet airplane engine. Comparable nanomotors run significantly more slowly, from 14 RPMs to 500 RPMs, and have only rotated for a few seconds up to a few minutes.

Looking forward, nanomotors could advance the field of nanoelectromechanical systems (NEMS), an area focused on developing miniature machines that are more energy efficient and less expensive to produce. In the near future, the Cockrell School researchers believe their nanomotors could provide a new approach to controlled biochemical drug delivery to live cells.

To test its ability to release drugs, the researchers coated the nanomotor's surface with biochemicals and initiated spinning. They found that the faster the nanomotor rotated, the faster it released the drugs.

"We were able to establish and control the molecule release rate by mechanical rotation, which means our nanomotor is the first of its kind for controlling the release of drugs from the surface of nanoparticles," Fan said. "We believe it will help advance the study of drug delivery and cell-to-cell communications."

The researchers address two major issues for nanomotors so far: assembly and controls. The team built and operated the nanomotor using a patent-pending technique that Fan invented while studying at Johns Hopkins University. The technique relies on AC and DC electric fields to assemble the nanomotor's parts one by one.

In experiments, the researchers used the technique to turn the nanomotors on and off and propel the rotation either clockwise or counterclockwise. The researchers found that they could position the nanomotors in a pattern and move them in a synchronized fashion, which makes them more powerful and gives them more flexibility.

Fan and her team plan to develop new mechanical controls and chemical sensing that can be integrated into nanoelectromechanical devices. But first they plan to test their nanomotors near a live cell, which will allow Fan to measure how they deliver molecules in a controlled fashion.

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Lithium-sulfur batteries last longer with nanomaterial-packed cathode

Lithium-sulfur batteries last longer with nanomaterial-packed cathode

  8:49:00 PM    Science Lover

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Electric vehicles could travel farther and more renewable energy could be stored with lithium-sulfur batteries that use a unique powdery nanomaterial.

Pacific Northwest National Laboratory developed
a nickel-based metal organic framework, shown here
in an illustration, to hold onto polysulfide molecules
in the cathodes of lithium-sulfur batteries and extend
the batteries' lifespans. The colored spheres in this i
mage represent the 3D material's tiny pores into with
the polysulfides become trapped.
Credit: Pacific Northwest National Laboratory

Researchers added the powder, a kind of nanomaterial called a metal organic framework, to the battery's cathode to capture problematic polysulfides that usually cause lithium-sulfur batteries to fail after a few charges. A paper describing the material and its performance was published online April 4 in the American Chemical Society journal Nano Letters.

"Lithium-sulfur batteries have the potential to power tomorrow's electric vehicles, but they need to last longer after each charge and be able to be repeatedly recharged," said materials chemist Jie Xiao of the Department of Energy's Pacific Northwest National Laboratory. "Our metal organic framework may offer a new way to make that happen."

Today's electric vehicles are typically powered by lithium-ion batteries. But the chemistry of lithium-ion batteries limits how much energy they can store. As a result, electric vehicle drivers are often anxious about how far they can go before needing to charge. One promising solution is the lithium-sulfur battery, which can hold as much as four times more energy per mass than lithium-ion batteries. This would enable electric vehicles to drive farther on a single charge, as well as help store more renewable energy. The down side of lithium-sulfur batteries, however, is they have a much shorter lifespan because they can't currently be charged as many times as lithium-ion batteries.

Energy Storage 101

The reason can be found in how batteries work. Most batteries have two electrodes: one is positively charged and called a cathode, while the second is negative and called an anode. Electricity is generated when electrons flow through a wire that connects the two. To control the electrons, positively charged atoms shuffle from one electrode to the other through another path: the electrolyte solution in which the electrodes sit.

The lithium-sulfur battery's main obstacles are unwanted side reactions that cut the battery's life short. The undesirable action starts on the battery's sulfur-containing cathode, which slowly disintegrates and forms molecules called polysulfides that dissolve into the liquid electrolyte. Some of the sulfur—an essential part of the battery's chemical reactions—never returns to the cathode. As a result, the cathode has less material to keep the reactions going and the battery quickly dies.

New materials for better batteries

Researchers worldwide are trying to improve materials for each battery component to increase the lifespan and mainstream use of lithium-sulfur batteries. For this research, Xiao and her colleagues honed in on the cathode to stop polysulfides from moving through the electrolyte.

Many materials with tiny holes have been examined to physically trap polysulfides inside the cathode. Metal organic frameworks are porous, but the added strength of PNNL's material is its ability to strongly attract the polysulfide molecules.

The framework's positively charged nickel center tightly binds the polysulfide molecules to the cathodes. The result is a coordinate covalent bond that, when combined with the framework's porous structure, causes the polysulfides to stay put.

"The MOF's highly porous structure is a plus that further holds the polysulfide tight and makes it stay within the cathode," said PNNL electrochemist Jianming Zheng.

Nanomaterial is key

Metal organic frameworks—also called MOFs—are crystal-like compounds made of metal clusters connected to organic molecules, or linkers. Together, the clusters and linkers assemble into porous 3-D structures. MOFs can contain a number of different elements. PNNL researchers chose the transition metal nickel as the central element for this particular MOF because of its strong ability to interact with sulfur.

During lab tests, a lithium-sulfur battery with PNNL's MOF cathode maintained 89 percent of its initial power capacity after 100 charge-and discharge cycles. Having shown the effectiveness of their MOF cathode, PNNL researchers now plan to further improve the cathode's mixture of materials so it can hold more energy. The team also needs to develop a larger prototype and test it for longer periods of time to evaluate the cathode's performance for real-world, large-scale applications.

PNNL is also using MOFs in energy-efficient adsorption chillers and to develop new catalysts to speed up chemical reactions.

"MOFs are probably best known for capturing gases such as carbon dioxide," Xiao said. "This study opens up lithium-sulfur batteries as a new and promising field for the nanomaterial."

This research was funded by the Department of Energy's Office of Energy Efficiency and Renewable Energy. Researchers analyzed chemical interactions on the MOF cathode with instruments at EMSL, DOE's Environmental Molecular Sciences Laboratory at PNNL.

In January, a Nature Communications paper by Xiao and some of her PNNL colleagues described another possible solution for lithium-sulfur batteries: developing a hybrid anode that uses a graphite shield to block polysulfides.

Source: http://phys.org/news/2014-04-lithium-sulfur-batteries-longer-nanomaterial-packed-cathode.html

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Future of energy storage with Graphite + Water

Future of energy storage with Graphite + Water

  1:56:00 PM    Science Lover

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A combination of two ordinary materials – graphite and water – could produce energy storage systems that perform on par with lithium ion batteries, but recharge in a matter of seconds and have an almost indefinite lifespan.

Graphene sheets. Credit: Gengping Jiang

Dr. Dan Li, of the Monash University Department of Materials Engineering, and his research team have been working with a material called graphene, which could form the basis of the next generation of ultrafast energy storage systems.

“Once we can properly manipulate this material, your iPhone, for example, could charge in a few seconds, or possibly faster.” said Dr. Li.

Graphene is the result of breaking down graphite, a cheap, readily available material commonly used in pencils, into layers one atom thick. In this form, it has remarkable properties.

Graphene is strong, chemically stable, an excellent conductor of electricity and, importantly, has an extremely high surface area.

Dr. Li said these qualities make graphene highly suitable for energy storage applications.



“The reason graphene isn’t being used everywhere is that these very thin sheets, when stacked into a usable macrostructure, immediately bond together, reforming graphite. When graphene restacks, most of the surface area is lost and it doesn’t behave like graphene anymore.”

Now, Dr. Li and his team have discovered the key to maintaining the remarkable properties of separate graphene sheets: water. Keeping graphene moist – in gel form – provides repulsive forces between the sheets and prevents re-stacking, making it ready for real-world application.

“The technique is very simple and can easily be scaled up. When we discovered it, we thought it was unbelievable. We’re taking two basic, inexpensive materials – water and graphite – and making this new nanomaterial with amazing properties,” said Dr. Li.

When used in energy devices, graphene gel significantly outperforms current carbon-based technology, both in terms of the amount of charge stored and how fast the charges can be delivered.

Dr. Li said the benefits of developing this new nanotechnology extend beyond consumer electronics.

“High-speed, reliable and cost-effective energy storage systems are critical for the future viability of electricity from renewable resources. These systems are also the key to large-scale adoption of electrical vehicles.

“Graphene gel is also showing promise for use in water purification membranes, biomedical devices and sensors.”

Provided by Monash University

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Researchers clarify properties of 'confined' water within single-walled carbon nanotube pores

Researchers clarify properties of 'confined' water within single-walled carbon nanotube pores

  11:02:00 PM    Science Lover

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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.

This global temperature-diameter (T-D) phase diagram
of water inside SWCNTs shows that, depending on
the water content, hollow or filled ice will form. On the
right, hollow- and filled-ice nanotubes can be calculated
at low temperature for SWCNTs with diameters indicated
with (a) and (b) in the lower portion of the phase diagram.
Credit: Yutaka Maniwa

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 Figure) 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.

Provided by American Institute of Physics

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