Super-elastic Conducting Nano Fibers for Artificial Muscles, Sensors , robots and exoskeletons

An international research team based at The University of Texas at Dallas has made electrically conducting fibers that can be reversibly stretched to over 14 times their initial length and whose electrical conductivity increases 200-fold when stretched.

                                                 

UT Dallas scientists have constructed novel fibers by wrapping sheets of tiny carbon nanotubes to form a sheath around a long rubber core. This illustration shows complex two-dimensional buckling, shown in yellow, of the carbon nanotube sheath/rubber-core fiber. The buckling results in a conductive fiber with super elasticity and novel electronic properties.credit:ut dellas

           

The research team is using the new fibers to make artificial muscles, as well as capacitors whose energy storage capacity increases about tenfold when the fibers are stretched. Fibers and cables derived from the invention might one day be used as interconnects for super-elastic electronic circuits; robots and exoskeletons having great reach; morphing aircraft; giant-range strain sensors; failure-free pacemaker leads; and super-stretchy charger cords for electronic devices.

In a study published in the July 24 issue of the journal Science, the scientists describe how they constructed the fibers by wrapping lighter-than-air, electrically conductive sheets of tiny carbon nanotubes to form a jelly-roll-like sheath around a long rubber core.

The new fibers differ from conventional materials in several ways. For example, when conventional fibers are stretched, the resulting increase in length and decrease in cross-sectional area restricts the flow of electrons through the material. But even a “giant” stretch of the new conducting sheath-core fibers causes little change in their electrical resistance, said Dr. Ray Baughman, senior author of the paper and director of the Alan G. MacDiarmid NanoTech Institute at UT Dallas.

One key to the performance of the new conducting elastic fibers is the introduction of buckling into the carbon nanotube sheets. Because the rubber core is stretched along its length as the sheets are being wrapped around it, when the wrapped rubber relaxes, the carbon nanofibers form a complex buckled structure, which allows for repeated stretching of the fiber.

“Think of the buckling that occurs when an accordion is compressed, which makes the inelastic material of the accordion stretchable,” said Baughman, the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas.

“We make the inelastic carbon nanotube sheaths of our sheath-core fibers super stretchable by modulating large buckles with small buckles, so that the elongation of both buckle types can contribute to elasticity. These amazing fibers maintain the same electrical resistance, even when stretched by giant amounts, because electrons can travel over such a hierarchically buckled sheath as easily as they can traverse a straight sheath.”

Dr. Zunfeng Liu, lead author of the study and a research associate in the NanoTech Institute, said the structure of the sheath-core fibers “has further interesting and important complexity.” Buckles form not only along the fiber’s length, but also around its circumference.

“Shrinking the fiber’s circumference during fiber stretch causes this second type of reversible hierarchical buckling around its circumference, even as the buckling in the fiber direction temporarily disappears,” Liu said. “This novel combination of buckling in two dimensions avoids misalignment of nanotube and rubber core directions, enabling the electrical resistance of the sheath-core fiber to be insensitive to stretch.”

By adding a thin overcoat of rubber to the sheath-core fibers and then another carbon nanotube sheath, the researchers made strain sensors and artificial muscles in which the buckled nanotube sheaths serve as electrodes and the thin rubber layer is a dielectric, resulting in a fiber capacitor. These fiber capacitors exhibited a capacitance change of 860 percent when the fiber was stretched 950 percent.

“No presently available material-based strain sensor can operate over nearly as large a strain range,” Liu said.

Adding twist to these double-sheath fibers resulted in fast, electrically powered torsional — or rotating — artificial muscles that could be used to rotate mirrors in optical circuits or pump liquids in miniature devices used for chemical analysis, said Dr. Carter Haines BS’11 PhD’15, a research associate in the NanoTech Institute and an author of the paper.

  In the laboratory, Nan Jiang, a research associate in the NanoTech Institute, demonstrated that the conducting elastomers can be fabricated in diameters ranging from the very small — about 150 microns, or twice the width of a human hair — to much larger sizes, depending on the size of the rubber core. “Individual small fibers also can be combined into large bundles and plied together like yarn or rope,” she said.

“This technology could be well-suited for rapid commercialization,” said Dr. Raquel Ovalle-Robles MS’06 PhD’08, an author on the paper and chief research and intellectual properties strategist at Lintec of America’s Nano-Science & Technology Center.

“The rubber cores used for these sheath-core fibers are inexpensive and readily available,” she said. “The only exotic component is the carbon nanotube aerogel sheet used for the fiber sheath.”

Last year, UT Dallas licensed to Lintec of America a process Baughman’s team developed to transform carbon nanotubes into large-scale structures, such as sheets. Lintec opened its Nano-Science & Technology Center in Richardson, Texas, less than 5 miles from the UT Dallas campus, to manufacture carbon nanotube aerogel sheets for diverse applications.

The Science research was supported by the Air Force Office of Scientific Research, the Robert A. Welch Foundation, the U.S. Army, the National Institutes of Health, the National Science Foundation and the Office of Naval Research. Several funding sources from China and Brazil also contributed.

In addition to Baughman, Liu, Haines, Jiang and Ovalle-Robles, paper authors based at UT Dallas’ NanoTech Institute are research scientists Dr. Shaoli Fang and Dr. Márcio Lima, and research associates Dr. Xavier Lépro and Dr. Jiangtao Di. Contributors based in the UT Dallas Department of Mechanical Engineering include Dr. Hongbing Lu, professor; Dr. Dong Qian, associate professor; and Xuemin Wang, research assistant. Researchers also contributed from universities in Florida, China and Brazil. 

source: UT Dellas News centre,July 23, 2015 press release  link : clickhere

recyclable and cleanable chip

A light-triggered cleanable, recyclable chip makes fabrication feasible for all

Throw away the detergent and forgo the elbow grease: pesky proteins can now be removed from surfaces by simply exposing them to light, thanks to a reusable titania template developed by A*STAR researchers1.
                                                             

From left to right: Mark Moxey, Karen Chong and MSM Saifullah from the A*STAR Institute of Materials Research and Engineering.

credit :© 2015 A*STAR Institute of Materials Research and Engineering

Biologists have many reasons to pattern surfaces with proteins, from creating highly selective biosensors to studying fundamental processes such as tissue formation. What they don’t want, however, is for the proteins to stay on the surface indefinitely. Unfortunately, ridding a surface of proteins is a complicated and time-consuming task, which means that the majority of biologists typically throw away their substrates after a single use — leading to a high cost for consumables. Moreover, due to the complexity of fabrication systems, biologists usually outsource their chip manufacturing to engineers, which introduces delays and further exacerbates cost.

Karen Chong and her team at the A*STAR Institute of Materials Research and Engineering in Singapore recognized that these delays and costs could be avoided by designing a fabrication technique that non-engineers could use. “We wanted to demonstrate that fabrication and patterning techniques could move away from the traditional domains of microelectronics,” she recalls. “Specifically, we wanted to create fabrication techniques that could easily be adopted and replicated by biologists.”

Chong notes that to be practical, fabrication techniques must be either easy to use or have the potential to be scaled up to produce commercial quantities. Consequently, she and the team focused on two techniques: interferometric lithography for the former and nanoimprint lithography for the latter.

“Interferometric lithography techniques can be easily replicated by biologists without the need for a very complex or costly set-up in their laboratories,” she explains. “While nanoimprinting is not practical for smaller labs, it does allow us to scale up these samples into larger-area substrates.”

Both approaches yielded surfaces with titania nanostructures (see image) that were then covered with protein-resistant silanes. Exposure to ultraviolet light degrades the silanes, which allows proteins to adhere to the selected regions. After the protein-patterned substrates have served their purpose, Chong describes how “the proteins on the chips can be quickly removed, by just exposing the used substrates to ultraviolet light, without the need for elaborate cleaning methods.” The substrates can then be immediately reused without the need for further preparation.

“With the recyclable chip and the technique that we have demonstrated, fabrication techniques are no longer the exclusive domain of engineers,” remarks Chong.

source:A*STAR research  link : click here

A Most Singular Nano-Imaging Technique : Berkeley Lab’s SINGLE Provides Images of Individual Nanoparticles in Solution

                                                                    

SINGLE uses in situ TEM imaging of platinum nanocrystals freely rotating in a graphene liquid cell to determine the 3D structures of individual colloidal nanoparticles.

Just as proteins are one of the basic building blocks of biology, nanoparticles can serve as the basic building blocks for next generation materials. In keeping with this parallel between biology and nanotechnology, a proven technique for determining the three dimensional structures of individual proteins has been adapted to determine the 3D structures of individual nanoparticles in solution.

A multi-institutional team of researchers led by the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), has developed a new technique called “SINGLE” that provides the first atomic-scale images of colloidal nanoparticles. SINGLE, which stands for 3D Structure Identification of Nanoparticles by Graphene Liquid Cell Electron Microscopy, has been used to separately reconstruct the 3D structures of two individual platinum nanoparticles in solution.

“Understanding structural details of colloidal nanoparticles is required to bridge our knowledge about their synthesis, growth mechanisms, and physical properties to facilitate their application to renewable energy, catalysis and a great many other fields,” says Berkeley Lab director and renowned nanoscience authority Paul Alivisatos, who led this research. “Whereas most structural studies of colloidal nanoparticles are performed in a vacuum after crystal growth is complete, our SINGLE method allows us to determine their 3D structure in a solution, an important step to improving the design of nanoparticles for catalysis and energy research applications.”

     Alivisatos, who also holds the Samsung Distinguished Chair in Nanoscience and Nanotechnology at the University of California Berkeley, and directs the Kavli Energy NanoScience Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper detailing this research in the journal Science. The paper is titled “3D Structure of Individual Nanocrystals in Solution by Electron Microscopy.” The lead co-authors are Jungwon Park of Harvard University, Hans Elmlund of Australia’s Monash University, and Peter Ercius of Berkeley Lab. Other co-authors are Jong Min Yuk, David Limmer, Qian Chen, Kwanpyo Kim, Sang Hoon Han, David Weitz and Alex Zettl.

      

Colloidal nanoparticles are clusters of hundreds to thousands of atoms suspended in a solution whose collective chemical and physical properties are determined by the size and shape of the individual nanoparticles. Imaging techniques that are routinely used to analyze the 3D structure of individual crystals in a material can’t be applied to suspended nanomaterials because individual particles in a solution are not static. The functionality of proteins are also determined by their size and shape, and scientists who wanted to image 3D protein structures faced a similar problem. The protein imaging problem was solved by a technique called “single-particle cryo-electron microscopy,” in which tens of thousands of 2D transmission electron microscope (TEM) images of identical copies of an individual protein or protein complex frozen in random orientations are recorded then computationally combined into high-resolution 3D reconstructions. Alivisatos and his colleagues utilized this concept to create their SINGLE technique.

                                                           

The Berkeley Lab GLC improves the resolution of TEM imaging with a viewing window made from a graphene sheet that is only a single atom thick.

“In materials science, we cannot assume the nanoparticles in a solution are all identical so we needed to develop a hybrid approach for reconstructing the 3D structures of individual nanoparticles,” says co-lead author of the Science paper Peter Ercius, a staff scientist with the National Center for Electron Microscopy (NCEM) at the Molecular Foundry, a DOE Office of Science User Facility.

         “SINGLE represents a combination of three technological advancements from TEM imaging in biological and materials science,” Ercius says. “These three advancements are the development of a graphene liquid cell that allows TEM imaging of nanoparticles rotating freely in solution, direct electron detectors that can produce movies with millisecond frame-to-frame time resolution of the rotating nanocrystals, and a theory for ab initio single particle 3D reconstruction.”

The graphene liquid cell (GLC) that helped make this study possible was also developed at Berkeley Lab under the leadership of Alivisatos and co-author Zettl, a physicist who also holds joint appointments with Berkeley Lab, UC Berkeley and Kavli ENSI. TEM imaging uses a beam of electrons rather than light for illumination and magnification but can only be used in a high vacuum because molecules in the air disrupt the electron beam. Since liquids evaporate in high vacuum, samples in solutions must be hermetically sealed in special solid containers – called cells – with a very thin viewing window before being imaged with TEM. In the past, liquid cells featured silicon-based viewing windows whose thickness limited resolution and perturbed the natural state of the sample materials. The GLC developed at Berkeley lab features a viewing window made from a graphene sheet that is only a single atom thick.

“The GLC provides us with an ultra-thin covering of our nanoparticles while maintaining liquid conditions in the TEM vacuum,” Ercius says. “Since the graphene surface of the GLC is inert, it does not adsorb or otherwise perturb the natural state of our nanoparticles.”

  Working at NCEM’s TEAM I, the world’s most powerful electron microscope, Ercius, Alivisatos and their colleagues were able to image in situ the translational and rotational motions of individual nanoparticles of platinum that were less than two nanometers in diameter. Platinum nanoparticles were chosen because of their high electron scattering strength and because their detailed atomic structure is important for catalysis.

“Our earlier GLC studies of platinum nanocrystals showed that they grow by aggregation, resulting in complex structures that are not possible to determine by any previously developed method,” Ercius says. “Since SINGLE derives its 3D structures from images of individual nanoparticles rotating freely in solution, it enables the analysis of heterogeneous populations of potentially unordered nanoparticles that are synthesized in solution, thereby providing a means to understand the structure and stability of defects at the nanoscale.”

The next step for SINGLE is to recover a full 3D atomic resolution density map of colloidal nanoparticles using a more advanced camera installed on TEAM I that can provide 400 frames-per-second and better image quality.

“We plan to image defects in nanoparticles made from different materials, core shell particles, and also alloys made of two different atomic species,” Ercius says.

This research was primarily supported by the DOE Office of Science.

source: Berkely labs   link: click here