Showing Spotlights 177 - 184 of 304 in category Carbon Nanotubes (newest first):
Since SWCNTs are sensitive to their chemical environment, they can be intentionally doped by a variety of dopants such as iron chloride, ammonia or nitrogen dioxide. But they can also be unintentionally doped. Scientists have known for some time that something funny happens when nanotubes are sonicated in certain solvents - sometimes their electronic properties change. Since mass produced nanotubes are clumped into bundles and ropes, they need to be dispersed prior to further processing in order to separate the individual nanotubes. A popular way of doing this is by exposing the CNT samples to ultrasonic pressure waves. Adding a dispersing reagent into the solution will accelerate the dispersion effect. New research now sheds light on how and why the electronic structure of carbon nanotubes changes during sonication.
Sep 29th, 2008
The processes by which molecules pass through pores in thin films and biological membranes are essential for understanding various physical, chemical and biological phenomena. For instance, the fundamental behavior of molecules in porous solids and their transfer through cell membranes necessarily involves a process of molecules passing through pores - knowledge that, for instance, is crucial for the development of nanotechnology-based hydrogen storage materials for fuel tanks. So far, research methods have been based on studying the statistical average of the behavior of groups of molecules; there were no experimental approaches that examined the interaction of a single molecule with a pore. There has been a lack of experimental methods that can obtain information on the structure and orientation of the molecules as they pass through a pore, and their interactions with the pore during passage. Researchers in Japan have now succeeded for the first time in observing a long chain of a fullerene-labeled hydrocarbon passing through a nanometer-size pore in the wall of a carbon nanotube as if it were alive.
Sep 22nd, 2008
Pristine carbon nanotubes (CNTs) are insoluble in many liquids such as water, polymer resins, and most solvents. This means they are difficult to evenly disperse in a liquid matrix such as epoxies and other polymers, complicating efforts to utilize CNTs' outstanding physical properties in the manufacture of nanocomposite materials, as well as in other practical nanotechnology applications which require preparation of uniform mixtures of CNTs with many different organic, inorganic, and polymeric materials. To make nanotubes more easily dispersible in liquids, it is necessary to physically or chemically attach certain molecules, or functional groups, to their sidewalls without significantly changing the nanotubes' desirable properties. This process is called functionalization. Numerous nanotechnology research projects around the world are dedicated to developing various kinds of CNT-based electrochemical devices through the rational functionalization of CNTs.
Sep 17th, 2008
Current production methods for carbon nanotubes (CNTs) result in units with different diameter, length, chirality and electronic properties, all packed together in bundles, and often blended with some amount of amorphous carbon. These mixtures are of little practical use since many advanced applications, especially for nanoelectronics, are sensitively dependent on tube structures. Consequently, the separation of metallic and semiconducting CNTs is essential for future applications and studies. The tube diameter of semiconducting nanotubes is also important because the band gap depends on it. Separation of nanotubes according to desired properties is still proving to be a challenging task, especially single-walled carbon nanotube (SWCNT) sorting, because the composition and chemical properties of SWCNTs of different types are very similar, making conventional separation techniques inefficient. The separation techniques for SWCNTs explored to date rely on preferential electron transfer on metallic SWCNTs treated with diazonium salts, dielectrophoresis, enhanced chemical affinity of semiconducting SWCNTs with octadecylamine, and wrapping of SWCNTs with single-stranded DNA.
Sep 16th, 2008
Carbon nanotubes are considered a promising material system not only for nanoelectronics but also for nanophotonics - the manipulation and emission of light using nanoscale materials and devices. By trying to understand the electrical properties of carbon nanotubes (CNTs) through their light emission, scientists are paving the way for CNTs' integration in optical applications. Embedding spatially isolated CNTs into an optical microcavity is a promising means of controlling and improving their radiative properties. The control of these CNT properties, including emission wavelength, spectral width, emission direction and radiative yield through optical confinement, opens the door for their use in integrated nanophotonic circuits. Cavity controlled nanotube emitters could potentially find use in quantum optics, quantum communication, and integrated nanophotonic circuits and may ultimately lead to low threshold on-chip nanolasers.
Sep 9th, 2008
The demand for the raw materials of the nanotechnology revolution - nanoparticles, carbon nanotubes, fullerenes, quantum dots, etc - is rising explosively and large chemical companies keep expanding their production capacities. These industrial scale systems often depend on precious input materials and energy-hogging processes. However, there are vast amounts of 'useless' natural materials literally lying around - rocks and stones - which could find their way into nanotechnology.Researchers in Germany have made a proof of concept demonstration that using natural nanostructures found in lava rocks is suitable for nanomaterial synthesis and for use in catalysis for production of butadiene and styrene.
Sep 2nd, 2008
Carbon nanotubes (CNTs) have been hyped as the wunderkind material of the 21st century. And while researchers have developed numerous CNT applications, ranging from nanoelectronics to nanomedicine and military armor, the actual properties of CNTs fell way short of what the theory predicted. For instance, quantum mechanics calculations predict that defect-free single-walled carbon nanotubes possess a tensile strength of well over 100 gigapascals - which translates into the ability to endure weight of over 10,000 kg on a cable with a cross-section of 1 square millimeter. In practice, CNT tensile strength of only up to 28 GPa have been measured. The problem lies not so much with the actual CNTs but rather with the mechanical tests that have been employed so far. It is very difficult to produce testable samples without damaging the tubes (which in turn adversely affects their properties), and to image the test with high enough resolution to determine the exact nature of the fracture. First experimental measurements of the mechanical properties of carbon nanotubes have now been made that directly correspond to the theoretical predictions.
Aug 14th, 2008
Generally, a surface either loves a liquid drop (then it's called solvophilic - wetting) or hates it (called solvophobic - repulsion) when it lands, depending on several parameters of both the surface - like geometric roughness asperities or ups and downs and chemical composition - and the liquid - like surface tension or tendency of solvation. When water is the liquid the terms hydrophilic and hydrophobic are used respectively for this and for oil similar terms like oleophilic and oleophobic. Advanced material engineering techniques can structure surfaces that allow dynamic tuning of their wettability all the way from superhydrophobic behavior to almost complete wetting - but these surfaces so far only work with high-surface-tension liquids. Just recently, researchers in India have developed a superhydrophobic (where the contact angle between the droplet and the surface is approaching 180 degrees) carbon nanotube (CNT) 'bucky paper' that shows fascinating wetting behavior as a result of an applied electric field, which could be remarkably tuned by changing key solution variables like ionic strength, nature of electrolyte, and pH of the droplet.
Aug 12th, 2008