Nanotube technology leading to new era of fast, lower-cost medical diagnostics

 Researchers at Oregon State University have tapped into the extraordinary power of carbon "nanotubes" to increase the speed of biological sensors, a technology that might one day allow a doctor to routinely perform lab tests in minutes, speeding diagnosis and treatment while reducing costs.

The new findings have almost tripled the speed of prototype nano-biosensors, and should find applications not only in medicine but in toxicology, environmental monitoring, new drug development and other fields.

The research was just reported in Lab on a Chip, a professional journal. More refinements are necessary before the systems are ready for commercial production, scientists say, but they hold great potential.

"With these types of sensors, it should be possible to do many medical lab tests in minutes, allowing the doctor to make a diagnosis during a single office visit," said Ethan Minot, an OSU assistant professor of physics. "Many existing tests take days, cost quite a bit and require trained laboratory technicians.

"This approach should accomplish the same thing with a hand-held sensor, and might cut the cost of an existing $50 lab test to about $1," he said.

The key to the new technology, the researchers say, is the unusual capability of carbon nanotubes. An outgrowth of nanotechnology, which deals with extraordinarily small particles near the molecular level, these nanotubes are long, hollow structures that have unique mechanical, optical and electronic properties, and are finding many applications.

In this case, carbon nanotubes can be used to detect a protein on the surface of a sensor. The nanotubes change their electrical resistance when a protein lands on them, and the extent of this change can be measured to determine the presence of a particular protein -- such as serum and ductal protein biomarkers that may be indicators of breast cancer.

The newest advance was the creation of a way to keep proteins from sticking to other surfaces, like fluid sticking to the wall of a pipe. By finding a way to essentially "grease the pipe," OSU researchers were able to speed the sensing process by 2.5 times.

Further work is needed to improve the selective binding of proteins, the scientists said, before it is ready to develop into commercial biosensors.

"Electronic detection of blood-borne biomarker proteins offers the exciting possibility of point-of-care medical diagnostics," the researchers wrote in their study. "Ideally such electronic biosensor devices would be low-cost and would quantify multiple biomarkers within a few minutes."

This work was a collaboration of researchers in the OSU Department of Physics, Department of Chemistry, and the University of California at Santa Barbara. A co-author was Vincent Remcho, professor and interim dean of the OSU College of Science, and a national expert in new biosensing technology.

The research was supported by the U.S. Army Research Laboratory through the Oregon Nanoscience and Microtechnologies Institute.

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:

Matthew R. Leyden, Robert J. Messinger, Canan Schuman, Tal Sharf, Vincent T. Remcho, Todd M. Squires, Ethan D. Minot. Increasing the detection speed of an all-electronic real-time biosensor. Lab on a Chip, 2012; 12 (5): 954 DOI: 10.1039/C2LC21020G

Fully printed carbon nanotube transistor circuits for displays

 Since the invention of liquid crystal displays in the mid-1960s, display electronics have undergone rapid transformation. Recently developed organic light-emitting diodes (OLEDs) have shown several advantages over LCDs, including their light weight, flexibility, wide viewing angles, improved brightness, high power efficiency and quick response.

OLED-based displays are now used in cell phones, digital cameras and other portable devices. But developing a lower-cost method for mass-producing such displays has been complicated by the difficulties of incorporating thin-film transistors that use amorphous silicon and polysilicon into the production process.

Now, researchers from Aneeve Nanotechnologies, a startup company at UCLA's on-campus technology incubator at the California NanoSystems Institute (CNSI), have used low-cost ink-jet printing to fabricate the first circuits composed of fully printed back-gated and top-gated carbon nanotube-based electronics for use with OLED displays. 

The startup includes collaborators from the departments of materials science and electrical engineering at the UCLA Henry Samueli School of Engineering and Applied Science and the department of electrical engineering at the University of Southern California.

In this innovative study, the team made carbon nanotube thin-film transistors with high mobility and a high on-off ratio, completely based on ink-jet printing. They demonstrated the first fully printed single-pixel OLED control circuits, and their fully printed thin-film circuits showed significant performance advantages over traditional organic-based printed electronics.

"This is the first practical demonstration of carbon nanotube-based printed circuits for display backplane applications," said Kos Galatsis, an associate adjunct professor of materials science at UCLA Engineering and a co-founder of Aneeve. "We have demonstrated carbon nanotubes' viable candidacy as a competing technology alongside amorphous silicon and metal-oxide semiconductor solution as a low-cost and scalable backplane option."

This distinct process utilizes an ink-jet printing method that eliminates the need for expensive vacuum equipment and lends itself to scalable manufacturing and roll-to-roll printing. The team solved many material integration problems, developed new cleaning processes and created new methods for negotiating nano-based ink solutions.

For active-matrix OLED applications, the printed carbon nanotube transistors will be fully integrated with OLED arrays, the researchers said. The encapsulation technology developed for OLEDs will also keep the carbon nanotube transistors well protected, as the organics in OLEDs are very sensitive to oxygen and moisture.

The technology incubator at the CNSI was established two years ago to nurture early-stage research and to help speed the commercial translation of technologies developed at UCLA. Aneeve Nanotechnologies LLC has been conducting proof-of-concept work at the tech incubator with the mission of developing superior, low-cost, high-performance electronics using nanotechnology solutions that bridge the gap between emerging and traditional platforms.

The research was published this month in the journal Nano Letters.

Story Source:

The above story is reprinted from materials provided by University of California - Los Angeles.

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

Journal Reference:

Pochiang Chen, Yue Fu, Radnoosh Aminirad, Chuan Wang, Jialu Zhang, Kang Wang, Kosmas Galatsis, Chongwu Zhou. Fully Printed Separated Carbon Nanotube Thin Film Transistor Circuits and Its Application in Organic Light Emitting Diode Control. Nano Letters, 2011; : 111122151948003 DOI: 10.1021/nl202765b

Two early stages of carbon nanotube growth discovered

 Boston College researchers have discovered two early-stage phases of carbon nanotube growth during plasma enhanced chemical vapor deposition, finding a disorderly tangle of tube growth that ultimately yields to orderly rows of the nanoscopic tubes, according to a report in the latest edition of the journal Nanotechnology.

By using a thin layer of catalyst, Professor of Physics Zhifeng Ren and researcher Dr. Hengzhi Wang discovered two previously overlooked stages of carbon nanotube growth, they report. The method yields a first stage where budding tubes appear randomly entangled, then a second stage of partially aligned tubes, then a third and final stage of tubes in full alignment, which is the standard used by researchers who produce carbon nanotubes for use in a range of materials and biomedical research.

"These growth phases are controlled by the thickness of the catalyst in use," said Wang. "Each stage, it turns out, has its own merit. Each stage has its own purpose."

In plasma enhanced chemical vapor deposition, carbon nanotubes are grown through the repeated accumulation of carbon atoms from the decomposition of gasses upon a catalyst particle, which creates multilayered carbon material on a substrate. Researchers have sought to create neatly aligned rows of millions of carbon nanotubes upon the substrates.

"We didn't know why we were seeing these nanotube configurations," said Ren, among the pioneers in the development of aligned carbon nanotubes. "This is really why you are a scientist. You see a new phenomenon and then you try to understand it."

Ren and Wang say that in the process of achieving the third stage of nanotube growth, the two earlier phases of growth have gone overlooked as each stage is etched away by the next application of plasma. Further masking these early-stage carbon nanotubes is the fact that they are not present when a thick catalyst is used, according to their findings.

The first stage tubes, produced in zero to four minutes, are described as a tangle of random large and small diameter carbon nanotubes. The second stage tubes, created in four to ten minutes, are generally smaller in diameter, but taller and only partially aligned.

Wang says that while these nanotubes are not in neat, orderly rows, they do have the advantage of offer a larger volumetric density and create a larger surface area, which could be an important development in the use of carbon nanotubes in heat transfer in thermal management. A potential application could involve in applying a thin coating of carbon nanotubes to an integrated circuit in order to draw away heat and efficiently cool the device.

After ten minutes of plasma etching, the early stage nanotubes have been washed away and the third stage tubes begin to emerge in tall, ordered rows upon the substrate. At this stage, the tubes themselves are shielded by makeshift "helmets" of catalyst particles, which effectively protect them during the last part of the growth process. Eventually, these last bits of catalyst are etched away as well.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Boston College.

Researchers power line-voltage light bulb with nanotube wire

 Cables made of carbon nanotubes are inching toward electrical conductivities seen in metal wires, and that may light up interest among a range of industries, according to Rice University researchers.

A Rice lab made such a cable from double-walled carbon nanotubes and powered a fluorescent light bulb at standard line voltage -- a true test of the novel material's ability to stake a claim in energy systems of the future.

The work appears this week in the Nature journal Scientific Reports.

Highly conductive nanotube-based cables could be just as efficient as traditional metals at a sixth of the weight, said Enrique Barrera, a Rice professor of mechanical engineering and materials science. They may find wide use first in applications where weight is a critical factor, such as airplanes and automobiles, and in the future could even replace traditional wiring in homes.

The cables developed in the study are spun from pristine nanotubes and can be tied together without losing their conductivity. To increase conductivity of the cables, the team doped them with iodine and the cables remained stable. The conductivity-to-weight ratio (called specific conductivity) beats metals, including copper and silver, and is second only to the metal with highest specific conductivity, sodium.

Yao Zhao, who recently defended his dissertation toward his doctorate at Rice, is the new paper's lead author. He built the demo rig that let him toggle power through the nanocable and replace conventional copper wire in the light-bulb circuit.

Zhao left the bulb burning for days on end, with no sign of degradation in the nanotube cable. He's also reasonably sure the cable is mechanically robust; tests showed the nanocable to be just as strong and tough as metals it would replace, and it worked in a wide range of temperatures. Zhao also found that tying two pieces of the cable together did not hinder their ability to conduct electricity.

The few centimeters of cable demonstrated in the present study seems short, but spinning billions of nanotubes (supplied by research partner Tsinghua University) into a cable at all is quite a feat, Barrera said. The chemical processes used to grow and then align nanotubes will ultimately be part of a larger process that begins with raw materials and ends with a steady stream of nanocable, he said. The next stage would be to make longer, thicker cables that carry higher current while keeping the wire lightweight. "We really want to go better than what copper or other metals can offer overall," he said.

The paper's co-authors are Tsinghua researcher Jinquan Wei, who spent a year at Rice partly supported by the Armchair Quantum Wire Project of Rice University's Smalley Institute for Nanoscale Science and Technology; Robert Vajtai, a Rice faculty fellow in mechanical engineering and materials science; and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science and professor of chemistry and chemical and biomolecular engineering.

The Research Partnership to Secure Energy for America, the Department of Energy and Air Force Research Laboratory supported the project.

Story Source:

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

Journal Reference:

Yao Zhao, Jinquan Wei, Robert Vajtai, Pulickel M. Ajayan, Enrique V. Barrera. Iodine doped carbon nanotube cables exceeding specific electrical conductivity of metals. Scientific Reports, 2011; 1 DOI: 10.1038/srep00083

Carbon nanotube composites for enzymes and cosmetics

 Toyohashi Tech researchers develop a low cost and efficient method for producing electrically conducting composites based on electrostatic adsorption of CNTs onto resin and ceramic particles for applications including the production of enzymes and cosmetics.

Hiroyuki Muto and colleagues at Japan’s Toyohashi University of Technology (Toyohashi Tech) have developed an innovative method for producing CNT (carbon nano-tube) resin composite material   that only requires 1/100 of the conventional amount of CNT additive to produce electrical conductivity in the composite material.

In this method, CNTs were mixed in an electrolyte solution and added to the composite, where the CNTs were adsorbed onto the surfaces of the resin particles due to electrostatic adsorption.  This procedure enabled the production of electrical conducting composites by the addition of a small quantity CNTs.

Importantly, the electrical conductivity of the composite material was easily controlled by changing the amount of electrolyte added to the composite; namely, the concentration of CNTs adsorption onto the resin particles.

Notably, this approach enables significant reductions in both the production costs and the production time compared with conventional methods for manufacturing conductive resins.

The researchers are confident that adding particles with charged surfaces will enable the production of a wide range of composite materials such as metals, ceramics, and polymers.  This method is expected to find applications in the production of enzymes and cosmetics.

This work is supported by a Grant-in-Aid for Young Scientists at NEDO (New Energy and Industrial Technology Development Organization).

Carbon nanotube structures changed by ‘attack’ from within, researchers discover

 A team of researchers involving scientists from The University of Nottingham has shown for the first time that chemical reactions at the nano-level which change the structure of carbon nanotubes can be sparked by an 'attack' from within.

The discovery challenges previous scientific thinking that the internal surface of the hollow nanostructures is chemically unreactive, largely restricting their use to that of an inert container or a 'nano-reactor' inside which other chemical reactions can take place.

Their research, published in the journal Nature Chemistry, shows that carbon nanotubes that have had their structures changed are exciting new materials that could be useful in the development of new technologies for gas storage devices, chemical sensors and parts of electronic devices such as transistors.

Dr Andrei Khlobystov, of the University's School of Chemistry, who led the work at Nottingham, said: "It has universally been accepted for some time now that the internal surface of carbon nanotubes -- or the concave side -- is chemically unreactive, and indeed we have been successfully using carbon nanotubes as nano-reactors.

"However, in the course of this new research we made the serendipitous discovery that in the presence of catalytically active transition metals inside the nanotube cavity, the nanotube itself can be involved in unexpected chemical reactions."

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. Dr Khlobystov and his research associates were recently involved in the discovery -- published in Nature Materials -- that nanotubes can be used as a catalyst for the production of nanoribbon, atomically thin strips of carbon created from carbon and sulphur atoms. These nanoribbons could potentially be used as new materials for the next generation of computers and data storage devices that are faster, smaller and more powerful.

In this latest research, the scientists found that an individual atom of Rhenium metal (Re) sets off a chemical reaction leading to the transformation of the inner wall of the nanotube. Initially, the attack by the Rhenium creates a small defect in the nanotube wall which then gradually develops into a nano-sized protrusion by 'eating' additional carbon atoms.

The protrusion then rapidly increases in size and seals itself off, forming a unique carbon structure dubbed a NanoBud, so called because the protrusion on the carbon nanotube resembles a bud on a stem.

Previously, NanoBuds were believed to be formed outside the nanotube through reactions on the outer surface with carbon molecules called fullerenes.

The new study demonstrates for the first time that they can be formed from within, provided that a transition metal atom with suitable catalytic activity is present within the nanotube.

In collaboration with the Electron Microscopy of Materials Science group at Ulm University in Germany, the scientists have even been able to capture 'on camera' the chemical reaction of the transition metal atom with the nanotube in real time at the atomic level using the latest Aberration-Corrected High Resolution Transmission Electron Microscopy (AC-HRTEM). Their videos show nanotubes with a diameter of around 1.5 nanometers, while the NanoBuds are just 1 nanometer across.

Story Source:

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

Journal Reference:

Thomas W. Chamberlain, Jannik C. Meyer, Johannes Biskupek, Jens Leschner, Adriano Santana, Nicholas A. Besley, Elena Bichoutskaia, Ute Kaiser, Andrei N. Khlobystov. Reactions of the inner surface of carbon nanotubes and nanoprotrusion processes imaged at the atomic scale. Nature Chemistry, 2011; DOI: 10.1038/nchem.1115

Disorder is key to nanotube mystery

Scientists often find strange and unexpected things when they look at materials at the nanoscale -- the level of single atoms and molecules. This holds true even for the most common materials, such as water.

Case in point: In the last couple of years, researchers have observed that water spontaneously flows into extremely small tubes of graphite or graphene, called carbon nanotubes. This unexpected observation is intriguing because carbon nanotubes hold promise in the emerging fields of nanofluidics and nanofiltration, where nanotubes might be able to help maintain tiny flows or separate impurities from water. However, no one has managed to explain why, at the molecular level, a stable liquid would want to confine itself to such a small area.

Now, using a novel method to calculate the dynamics of water molecules, Caltech researchers believe they have solved the mystery. It turns out that entropy, a measurement of disorder, has been the missing key.

"It's a pretty surprising result," says William Goddard, the Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics at Caltech and director of the Materials and Process Simulation Center. "People normally focus on energy in this problem, not entropy."

That's because water forms an extensive network of hydrogen bonds, which makes it very stable. Breaking those strong interactions requires energy. And since some bonds have to be broken in order for water to flow into small nanotubes, it would seem unlikely that water would do so freely.

"What we found is that it's actually a trade off," Goddard says. "You lose some of that good energy stabilization from the bonding, but in the process you gain in entropy."

Entropy is one of the driving forces that determine whether a process will occur spontaneously. It represents the number of ways a system can exist in a particular state. The more arrangements available to a system, the greater its disorder, and the higher the entropy. And in general, nature proceeds toward disorder.

When water is ideally bonded, all of the hydrogen bonds lock the molecules into place, restricting their freedom and keeping water's entropy low. What Goddard and postdoctoral scholar Tod Pascal found is that in the case of some nanotubes, water gains enough entropy by entering the tubes to outweigh the energy losses incurred by breaking some of its hydrogen bonds. Therefore, water flows spontaneously into the tubes.

Goddard and Pascal explain their findings in a paper recently published in the Proceedings of the National Academy of Sciences (PNAS). They looked at carbon nanotubes with diameters between 0.8 and 2.7 nanometers and found three different reasons why water would flow freely into the tubes, depending on diameter.

For the smallest nanotubes -- those between 0.8 and 1.0 nanometers in diameter -- the tubes are so minuscule that water molecules line up nearly single file within them and take on a gaslike state. That means the normal bonded structure of liquid water breaks down, giving the molecules greater freedom of motion. This increase in entropy draws water into the tubes.

At the next level, where the nanotubes have diameters between 1.1 and 1.2 nanometers, confined water molecules arrange themselves in stacked, icelike crystals. Goddard and Pascal found such nanotubes to be the perfect size -- a kind of Goldilocks match -- to accommodate crystallized water. These crystal-bonding interactions, not entropy, make it favorable for water to flow into the tubes.

On the largest scale studied -- involving tubes whose diameters are still only 1.4 to 2.7 nanometers wide -- the researchers found that the confined water molecules behave more like liquid water. However, once again, some of the normal hydrogen bonds are broken, so the molecules exhibit more freedom of motion within the tubes. And the gains in entropy more than compensate for the loss in hydrogen bonding energy.

Because the insides of the carbon nanotubes are far too small for researchers to examine experimentally, Goddard and Pascal studied the dynamics of the confined water molecules in simulations. Using a new method developed by Goddard's group with a supercomputer, they were able to calculate the entropy for the individual water molecules. In the past, such calculations have been difficult and extremely time-consuming. But the new approach, dubbed the two-phase thermodynamic model, has made the determination of entropy values relatively easy for any system.

"The old methods took eight years of computer processing time to arrive at the same entropies that we're now getting in 36 hours," Goddard says.

The team also ran simulations using an alternative description of water -- one where water had its usual properties of energy, density, and viscosity, but lacked its characteristic hydrogen bonding. In that case, water did not want to flow into the nanotubes, providing additional proof that water's naturally occurring low entropy due to extensive hydrogen bonding leads to it spontaneously filling carbon nanotubes when the entropy increases.

Goddard believes that carbon nanotubes could be used to design supermolecules for water purification. By incorporating pores with the same diameters as carbon nanotubes, he thinks a polymer could be made to suck water out of solution. Such a potential application points to the need for a greater understanding of water transport through carbon nanotubes.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by California Institute of Technology.

Journal Reference:

T. A. Pascal, W. A. Goddard, Y. Jung. From the Cover: Entropy and the driving force for the filling of carbon nanotubes with water. Proceedings of the National Academy of Sciences, 2011; 108 (29): 11794 DOI: 10.1073/pnas.1108073108

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

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 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.

 

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

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.

Free-standing single-walled carbon nanotube thin films

ScienceDaily (May 13, 2011) — Single-walled CNTs (SWCNTs) are a unique family of materials exhibiting diverse useful chemical and physical properties, researchers in Finland are demonstrating.

Thin films of SWCNTs have many unique properties such as high porosity and specific surface area, low density, high ratio of optical transmittance to sheet resistance, high thermal conductivity and chemical sensitivity, and tunable metallic and semiconducting properties.

Recently researchers from Department of Applied Physics at Aalto University (Finland) in collaboration with Canatu Ltd. (Finland) have discovered a simple and rapid method to prepare thin multifunctional single-walled carbon nanotube films without any substrate (free-standing films). Usually SWCNT films are prepared from suspensions of SWCNTs by a liquid filtration. This method typically involves several time and resource consuming and potentially detrimental liquid dispersion and purification steps ending up with dense SWCNT networks on a filter, which have a transfer issue. Moreover, preparation of free-standing films by the vacuum-filtration method is still a challenging task.

"Our method allows the preparation of SWCNT deposits both on different substrates and in the form of free-standing films during less than 15 s. This becomes possible due to the fact that the SWCNTs produced in the gas phase synthesis process gave very high purity and crystallinity, can be directly deposit from the gas to a substrate and accordingly be directly utilised without additional purification steps," says Dr. David P. Brown, CEO of the company Canatu Ltd, which commercializes the SWCNT films.

The method easily allows Canatu to alter the thickness of multifunctional free-standing SWCNT films from a sub-monolayer (when the amount of SWCNTs is insufficient to create a single continuous layer) to a few micrometers.

Collaboration with other Finnish universities

According to the researchers, the collaboration with other Finnish universities and institutions, Tampere University of Technology and Oulu University, was extremely important to investigate the unique properties and to demonstrate the multifunctionality of this unique material.

"We fabricated the state-of-the-art components for filtration of aerosol nanoparticles, transparent, flexible and highly conductive electrodes, extremely sensitive electrochemical sensors, polymer free saturable laser absorbers, gas heaters, thermo acoustic loudspeakers, and gas flow meters," says professor Esko I. Kauppinen, the leader of the research group.

SWCNT films - wide range of applications

"However, the wide range of applications is not limited to those reported in our paper. The superior mechanical and electrical properties of these films suggest potential uses in a broad range of other devices. As a filter, SWCNT films could be used for filtration of bacteria and viruses. The possibility to heat SWCNT films can be utilized for water or air sterilization. Additionally, since SWCNTs contain iron particles embedded inside them, one could exploit their magnetic properties. Their high strength coupled with high electrical conductivity could be employed in novel energy generators, electromagnetic interference shielding, flexible radio frequency identification tags, touch sensors, flat panel displays and static-charge dissipators. The ultrahigh surface area coupled with high electrical conductivity could be used in advanced solar cells and super capacitors," Dr. Albert G. Nasibulin, the leader of this project and the first author of the article related to the discovery of multifunctional free-standing SWCNTs concludes.

The results has been recently published in the journal ACS Nano.

Even though graphene has recently attracted much attention from the research community, some properties of SWCNTs, such as porosity, mechanical strength, and fine-tunability of optical and electrical properties, provide many applications where the flat, single-layered carbon structure cannot compete with its tubular 'brother'.

Story Source:

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

Journal Reference:

Albert G. Nasibulin, Antti Kaskela, Kimmo Mustonen, Anton S. Anisimov, Virginia Ruiz, Samuli Kivisto¨, Simas Rackauskas, Marina Y. Timmermans, Marko Pudas, Brad Aitchison, Marko Kauppinen, David P. Brown, Oleg G. Okhotnikov, Esko I. Kauppinen. Multifunctional Free-Standing Single-Walled Carbon Nanotube Films. ACS Nano, 2011; : 110310090902026 DOI: 10.1021/nn200338r

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

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