Engineers now Understand How Complex Carbon Nanostructures Form


CNT 041015 id39703Carbon nanotubes (CNTs) are microscopic tubular structures that engineers “grow” through a process conducted in a high-temperature furnace. The forces that create the CNT structures known as “forests” often are unpredictable and are mostly left to chance.
Now, a University of Missouri researcher has developed a way to predict how these complicated structures are formed (Carbon, “Integrated simulation of active carbon nanotube forest growth and mechanical compression”). By understanding how CNT arrays are created, designers and engineers can better incorporate the highly adaptable material into devices and products such as baseball bats, aerospace wiring, combat body armor, computer logic components and micro sensors used in biomedical applications.
Carbon Nanotube Forest
On the left is a scanning electron micrograph of a carbon nanotube forest. The figure on the right is a numerically simulated CNT forest. (Image: Matt Maschmann)
CNTs are much smaller than the width of a human hair and naturally form “forests” when they are created in large numbers (see photo). These forests, held together by a nanoscale adhesive force known as the van der Waals force, are categorized based on their rigidity or how they are aligned. For example, if CNTs are dense and well aligned, the material tends to be more rigid and can be useful for electrical and mechanical applications. If CNTs are disorganized, they tend to be softer and have entirely different sets of properties.
“Scientists are still learning how carbon nanotube arrays form,” said Matt Maschmann, assistant professor of mechanical and aerospace engineering in the College of Engineering at MU. “As they grow in relatively dense populations, mechanical forces combine them into vertically oriented assemblies known as forests or arrays. The complex structures they form help dictate the properties the CNT forests possess. We’re working to identify the mechanisms behind how those forests form, how to control their formation and thus dictate future uses for CNTs.”
Currently, most models that examine CNT forests analyze what happens when you compress them or test their thermal or conductivity properties after they’ve formed. However, these models do not take into account the process by which that particular forest was created and struggle to capture realistic CNT forest structure.
Experiments conducted in Maschmann’s lab will help scientists understand the process and ultimately help control it, allowing engineers to create nanotube forests with desired mechanical, thermal and electrical properties. He uses modeling to map how nanotubes grow into particular types of forests before attempting to test their resulting properties.
“The advantage of this approach is that we can map how different synthesis parameters, such as temperature and catalyst particle size, influence how nanotubes form while simultaneously testing the resulting CNT forests for how they will behave in one comprehensive simulation,” Maschmann said. “I am very encouraged that the model successfully predicts how they are formed and their mechanical behaviors. Knowing how nanotubes are organized and behave will help engineers better integrate CNTs in practical, everyday applications.”
Source: University of Missouri-Columbia
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‘Bending’ Elastic Waves with New Metamaterials that could have commercial applications


Elastic Sound Waves id38814Sound waves passing through the air, objects that break a body of water and cause ripples, or shockwaves from earthquakes all are considered “elastic” waves. These waves travel at the surface or through a material without causing any permanent changes to the substance’s makeup.
Now, engineering researchers at the University of Missouri have developed a material that has the ability to control these waves, creating possible medical, military and commercial applications with the potential to greatly benefit society (Nature Communications, “Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial”).

“Methods of controlling and manipulating subwavelength acoustic and elastic waves have proven elusive and difficult; however, the potential applications–once the methods are refined–are tremendous,” said Guoliang Huang, associate professor of mechanical and aerospace engineering in the College of Engineering at MU. “Our team has developed a material that, if used in the manufacture of new devices, could have the ability to sense sound and elastic waves. By manipulating these waves to our advantage, we would have the ability to create materials that could greatly benefit society–from imaging to military enhancements such as elastic cloaking–the possibilities truly are endless.”

chiral microstructures on a steel sheet
The fabrications were made in a steel sheet with lasers and are chiral microstructures, which means the top and bottom layers are identical in composition but arranged asymmetrically. It’s the first such material to be made out of a single medium. (Image: Guoliang Huang)
 
In the past, scientists have used a combination of materials such as metal and rubber to effectively ‘bend’ and control waves. Huang and his team designed a material using a single component: steel. The engineered structural material possesses the ability to control the increase of acoustical or elastic waves. Improvements to broadband signals and super-imaging devices also are possibilities.
The material was made in a single steel sheet using lasers to engrave “chiral,” or geometric microstructure patterns, which are asymmetrical to their mirror images (see photo). It’s the first such material to be made out of a single medium. Huang and his team intend to introduce elements they can control that will prove its usefulness in many fields and applications.
“In its current state, the metal is a passive material, meaning we need to introduce other elements that will help us control the elastic waves we send to it,” Huang said. “We’re going to make this material much more active by integrating smart materials like microchips that are controllable. This will give us the ability to effectively ‘tune in’ to any elastic sound or elastic wave frequency and generate the responses we’d like; this manipulation gives us the means to control how it reacts to what’s surrounding it.”
Going forward, Huang said there are numerous possibilities for the material to control elastic waves including super-resolution sensors, acoustic and medical hearing devices, as well as a “superlens” that could significantly advance super-imaging, all thanks to the ability to more directly focus the elastic waves.
Source: University of Missouri

Read more: Scientists ‘bend’ elastic waves with new metamaterials that could have commercial applications

Nanoparticles Harness Powerful Radiation Therapy for Cancer


Posted: May 17th, 2013

Nanoparticle harnesses powerful radiation therapy for cancer

(Nanowerk News) Researchers at the University of Missouri have demonstrated the ability to create a multi-layered harness nanoparticle that can safely encapsulate powerful alpha-emitting radioisotopes and target tumors. The resulting nanoparticles not only offer the possibility of delivering tumor-killing alpha emitters to tumors, but also sparing healthy tissue from radiation damage. J. David Robinson and his colleagues published their findings in the journal PLoS One (“Gold Coated Lanthanide Phosphate Nanoparticles for Targeted Alpha Generator Radiotherapy”).Typically, when radiation treatment is recommended for cancer patients, doctors are able to deliver radiation from a source outside the body or they might inject one of several radiopharmaceuticals that emit low-energy radiation known as beta particles. For years, scientists have been studying how to use “alpha emitters,” which are radioactive elements that release high-energy alpha particles that would more effectively damage cancer cells and trigger cell death. The challenge to using alpha emitters is that the decay elements, the so-called daughters, are themselves highly toxic and difficult to contain in the vicinity of the tumor, thus causing significant damage to healthy tissues.”If you think of beta particles as slingshots or arrows, alpha particles would be similar to cannon balls,” said Dr. Robertson. He explains that recent work has shown that alpha particles can be effective in treating cancer in specific instances. “For example, a current study using radium-223 chloride, which emits alpha particles, has been fast-tracked by the U.S. Food and Drug Administration because it has been shown to be effective in treating bone cancer. However, it only works for bone cancer because the element, radium, is attracted to the bone and stays there. We believe we have found a solution that will allow us to target alpha particles to other cancer sites in the body in an effective manner.”In their studies, Dr. Robertson and colleagues from Oak Ridge National Laboratory and the School of Medicine at the University of Tennessee in Knoxville used the isotope actinium-225, an element that when it decays produces a high-energy alpha particle and radioactive daughter elements, which are also capable of emitting alpha particles. Efforts to contain the daughter elements using traditional molecular constraints proved fruitless because the emitted alpha particles broke the chemical bonds necessary to hold the daughter elements in place.The Missouri team solved this problem by sequestering actinium-225 in the core of a gold-coated magnetic nanoparticle. The magnetic layer, comprised of gadolinium phosphate, serves to increase retention of the daughter elements while simplifying particle purification and the gold coating provides a surface to which tumor-targeting molecules can be attached. In the experiments described in their current publication, the researchers used an antibody that targets a receptor found on the surface of lung tumors.”Holding these alpha emitters in place is a technical challenge that researchers have been trying to overcome for 15 years,” Dr. Robertson said. “With our nanoparticle design, we are able to keep more than 80 percent of the element inside the nanoparticle 24 hours after it is created.” While alpha particles are extremely powerful, they do not travel very far, so when the nanoparticles get close to the targeted cancer cells, the alpha particles are more selective at damaging cancer cells but not surrounding cells.

Read more: http://www.nanowerk.com/news2/newsid=30558.php#ixzz2TiEg009k