Tag Archives: carbon nanofibers

Stretchable carbon nanotubes as supercapacitors

This Nov. 25, 2013 news item on phys.org was a bit of a walk down memory lane for me,

A mobile telephone display for your jacket sleeve, ECG probes for your workout clothes—wearable electronics are in demand. In order for textiles with built-in electronics to function over longer periods of time, all of the components need to be flexible and stretchable. In the journal Angewandte Chemie, Chinese researchers have now introduced a new type of supercapacitor that fulfills this requirement. Its components are fiber-shaped and based on carbon nanotubes.

The reference to a mobile telephone display on a jacket sleeve brought back memories of Nokia’s proposed Morph device,, from my Aug. 3, 2011 posting,

For anyone who’s not familiar with the Morph, it’s an idea that Nokia and the University of Cambridge’s Nanoscience Centre have been working on for the last few years. Originally announced as a type of flexible phone that you could wrap around your wrist, the Morph is now called a concept.  …

At the time I was writing about exploring the use of graphene to enable the morph (flexible phone). This latest work from China is focused on carbon nanotubes,. The Angewandte Chemie Nov. 25, 2013 press release, which originated the news item on phys.org,  provides more details,

For electronic devices to be incorporated into textiles or plastic films, their components must be stretchable. This is true for LEDS, solar cells, transistors, circuits, and batteries—as well as for the supercapacitors often used for static random access memory (SRAM). SRAM is often used as a cache in processors or for local storage on chips, as well as in devices that must maintain their data over several years with no source of power.

Previous stretchable electronic components have generally been produced in a conventional planar format, which has been an obstacle to their further development for use in small, lightweight, wearable electronics. Initial attempts to produce supercapacitors in the form of wires or fibers produced flexible—but not stretchable—components. However, stretchability is a required feature for a number of applications. For example, electronic textiles would easily tear if they were not stretchable.

A team led by Huisheng Peng at Fudan University has now developed a new family of highly stretchable, fiber-shaped, high-performance supercapacitors. The devices are made by a winding process with an elastic fiber at the core. The fiber is coated with an electrolyte gel and a thin layer of carbon nanotubes is wound around it like a sheet of paper. This is followed by a second layer of electrolyte gel, another layer of carbon nanotube wrap, and a final layer of electrolyte gel.

The delicate “sheets” of carbon nanotubes are produced by chemical vapor deposition and a spinning process. In the sheets this method produces, the tiny tubes are aligned in parallel. These types of layers display a remarkable combination of properties: They are highly flexible, tear-resistant, conductive, and thermally and mechanically stable. In the wound fibers, the two layers of carbon nanotubes act as electrodes. The electrolyte gel separates the electrodes from each other while stabilizing the nanotubes during stretching so that their alignment is maintained. This results in supercapacitor fibers with a high capacity that is maintained after many stretching cycles.

For the curious, here’s a link to and a citation for the paper,

A Highly Stretchable, Fiber-Shaped Supercapacitor by Zhibin Yang, Jue Deng, Xuli Chen, Jing Ren, and Prof. Huisheng Peng. Angewandte Chemie International Edition
Early View (Online Version of Record published before inclusion in an issue)Article first published online: 8 NOV 2013 DOI: 10.1002/anie.201307619

Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

US National Institute of Occupational Health and Safety sets recommendations for workplace exposure to carbon nanofibers/nanotubes

Earlier this week, the US National Institute of Occupational Health and Safety (NIOSH) set recommendations for workplace exposure to carbon nanotubes and carbon nanofibers. According to the Apr. 24, 2013 media advisory from the US Centers for Disease Control and Prevention (NIOSH’s parent agency), the recommendations have been issued in the new Current Intelligence Bulletin (CIB) no. 65. From CIB No. 65,

NIOSH is the leading federal agency conducting research and providing guidance on the occupational safety and health implications and applications of nanotechnology. As nanotechnology continues to expand into every industrial sector, workers will be at an increased risk of exposure to new nanomaterials. Today, nanomaterials are found in hundreds of products, ranging from cosmetics, to clothing, to industrial and biomedical applications. These nanoscale-based products are typically called “first generation” products of nanotechnology. Many of these nanoscale-based products are composed of engineered nanoparticles, such as metal oxides, nanotubes, nanowires, quantum dots, and carbon fullerenes (buckyballs), among others. Early scientific studies have indicated that some of these nanoscale particles may pose a greater health risk than the larger bulk form of these materials.

Results from recent animal studies indicate that carbon nanotubes (CNT) and carbon nanofibers (CNF) may pose a respiratory hazard. CNTs and CNFs are tiny, cylindrical, large aspect ratio, manufactured forms of carbon. There is no single type of carbon nanotube or nanofiber; one type can differ from another in shape, size, chemical composition (from residual metal catalysts or functionalization of the CNT and CNF) and other physical and chemical characteristics. Such variations in composition and size have added to the complexity of understanding their hazard potential. Occupational exposure to CNTs and CNFs can occur not only in the process of manufacturing them, but also at the point of incorporating these materials into other products and applications. A number of research studies with rodents have shown adverse lung effects at relatively low-mass doses of CNT and CNF, including pulmonary inflammation and rapidly developing, persistent fibrosis. Although it is not known whether similar adverse health effects occur in humans after exposure to CNT and CNF, the results from animal research studies indicate the need to minimize worker exposure.

This NIOSH CIB, (1) reviews the animal and other toxicological data relevant to assessing the potential non-malignant adverse respiratory effects of CNT and CNF, (2) provides a quantitative risk assessment based on animal dose-response data, (3) proposes a recommended exposure limit (REL) of 1 μg/m3 elemental carbon as a respirable mass 8-hour time-weighted average (TWA) concentration, [emphasis mine] and (4) describes strategies for controlling workplace exposures and implementing a medical surveillance program. The NIOSH REL is expected to reduce the risk for pulmonary inflammation and fibrosis. However, because of some residual risk at the REL and uncertainty concerning chronic health effects, including whether some types of CNTs may be carcinogenic, continued efforts should be made to reduce exposures as much as possible.

The recommended exposure, for those of us who can’t read the technical notation, translates to one microgram per cubic meter per eight-hour workday.  In other words, almost zero. Note that this is a recommendation and not a regulation. H/T Apr. 26, 2013 article by Elizabeth Wiese for USA Today

My Mar. 12, 2013 posting highlights some of the NIOSH research which preceded this recommendation.

Can you deflate your spike-studded balloon?

Researchers at North Carolina State University have developed a means for embedding carbon nanofiber spikes (or needles)  into an elastic-like membrane to create a studded balloon that could potentially be used for drug delivery according to a Jan. 15, 2013 news item on ScienceDailyOnline,

The research community is interested in finding new ways to deliver precise doses of drugs to specific targets, such as regions of the brain. One idea is to create balloons embedded with nanoscale spikes that are coated with the relevant drug. Theoretically, the deflated balloon could be inserted into the target area and then inflated, allowing the spikes on the balloon’s surface to pierce the surrounding cell walls and deliver the drug. The balloon could then be deflated and withdrawn.

But to test this concept, researchers first needed to develop an elastic material that is embedded with these aligned, nanoscale needles. That’s where the NC State [North Carolina State University] research team came in.

“We have now developed a way of embedding carbon nanofibers in an elastic silicone membrane and ensuring that the nanofibers are both perpendicular to the membrane’s surface and sturdy enough to impale cells,” says Dr. Anatoli Melechko, an associate professor of materials science and engineering at NC State and co-author of a paper on the work.

For some reason this description brought to mind medieval weapons of war such as this  flail (the ball

Flail-Klassischer-Flegel (Deutsch: Ein mit einem Lederriemen verzierter klassischer Flegel mit kugelförmigem Kopf und Kette als Faustriemen) Credit: Tim Avatar Bartel [downloaded from: http://en.wikipedia.org/wiki/File:Klassischer-Flegel.jpg]

Flail-Klassischer-Flegel (Deutsch: Ein mit einem Lederriemen verzierter klassischer Flegel mit kugelförmigem Kopf und Kette als Faustriemen) Credit: Tim Avatar Bartel [downloaded from: http://en.wikipedia.org/wiki/File:Klassischer-Flegel.jpg]

not the stick. There’s much more about the flail and its use as a weapon in this Wikipedia essay.

As for this nanoscaled balloon studded with carbon nanofibers, the Jan. 15, 2013 North Carolina State University news release, which originated the news item, goes on to describe the technique,

The researchers first “grew” the nanofibers on an aluminum bed, or substrate. They then added a drop of liquid silicone polymer. The polymer, nanofibers and substrate were then spun, so that centrifugal force spread the liquid polymer in a thin layer between the nanofibers – allowing the nanofibers to stick out above the surface. The polymer was then “cured,” turning the liquid polymer into a solid, elastic membrane. Researchers then dissolved the aluminum substrate, leaving the membrane embedded with the carbon nanofibers “needles.”

“This technique is relatively easy and inexpensive,” says Melechko, “so we are hoping this development will facilitate new research on targeted drug-delivery methods.”

The paper, “Transfer of Vertically Aligned Carbon Nanofibers to Polydimethylsiloxane (PDMS) while Maintaining their Alignment and Impalefection Functionality,” is published online in the journal ACS Applied Materials & Interfaces. Lead authors on the paper are Ryan Pearce, a Ph.D. student at NC State, and Justin Railsback, a former NC State student now pursuing a Ph.D. at Northwestern University. Co-authors are Melechko; Dr. Joseph Tracy, an assistant professor of materials science and engineering at NC State; Bryan Anderson and Mehmet Sarac, Ph.D. students at NC State; and Timothy McKnight of Oak Ridge National Laboratory.

It’s very interesting but I wonder how they plan to deflate the balloon and what will happen to the carbon nanofiber needles and balloon membrane after their usage?