MATERIALS: Nanotube Apps & Patents Increase

Recent discoveries have unveiled potential new uses for carbon nanotubes and the secret behind the strength of polymer nanocomposites. Patent filings are also on the rise.

Nanomaterials are expanding their applications, with carbon nanotubes leading the way. These remarkable carbon cylinders were recently found to fluoresce, which means they absorb one wavelength of light and emit another wavelength in response. This discovery paves the way for their application in biomedical tests and in nanoelectronics as light emitters. Indeed, industry's interest in this extraordinary molecule is mounting—as indicated by the steady increase in academic papers and patent filings on carbon nanotubes. Polymer nanocomposites are also receiving both academic and commercial interest. These composites are a blend of polymers and nanoscale components such as clays, carbon nanotubes and nanofibers. Such nanocomposites have amazing properties. For example, plastics reinforced with nanoparticles are lightweight and have remarkable strength. Furthermore, plastics loaded with nanocarbons have enhanced electrical and thermal conductivity—allowing them to remain viable as more polymer applications are demanding electrically active compounds. Scientists are also beginning to unlock the key to the extraordinary strength of these polymer nanocomposites. By finding out what makes these materials so tough, they can be made even tougher. Carbon Nanotubes Fluoresce Carbon nanotubes absorb light at visible or ultraviolet wavelengths and give off near-infrared light in response. This was the recent discovery of a team of Rice University chemists, headed by Nobel Laureate Professor Richard Smalley. This finding could lead to biomedical and nanoelectronics applications for carbon nanotubes. "Some of the most sophisticated biomedical tests today—such as MRI exams—cannot be performed in a doctor's office because the equipment is too large and too expensive to operate," says Smalley. "Because nothing in the human body fluoresces in the near-infrared spectrum, and human tissue is fairly transparent at that spectrum, one can envision a test apparatus based on this technology that would be as inexpensive and simple to use as ultrasound." Since nanotubes can be made in different diameters with each size emitting a different wavelength, it may be possible to design them to look for specific conditions within the body. By using multiple nanotubes while testing, many different diseases can be diagnosed at once. Chemist Bruce Weisman, whose photophysics research team conducted the fluorescence experiments with Smalley's group, says that these nanotubes can also be used to give off light in nanoscale integrated circuitry or nano-optoelectronics. Fluorescence joins an impressive list of carbon nanotube properties that already includes biocompatibility, copper-quality electrical conductivity, diamond-level thermal conductivity, strength 100 times that of steel at one-sixth the weight, and near-imperviousness to radiation and chemical destruction. Impending Economic Growth for Carbon Nanotubes? Academic papers published on carbon nanotubes have been on the rise and patent filings have been keeping up with this upswing, says a review in the journal Science. This flurry of publishing and patent filings implies industry's growing interest in nanotubes and increases the likelihood of their commercialization. Economists view publishing and patenting as signs of scientific activity and its shift into industry. In other words, they forecast economic viability. According to the review, around 1,500 scientific papers were published last year—compared to about 1,100 in 2000 and around 700 in 1999. Meanwhile, patent filings and issuances topped 200 in 2001—up from about 120 in 2000 and around 50 in 1999. Most of these filings and issuances (41%) involved the synthesis and processing of carbon nanotubes. Two applications already in the commercial market ranked second and third—electron emission such as displays with 25% and composites with 9%. Inventions in batteries and energy storage devices (7%), electronics (6%), hydrogen storage (6%), sensors (3%) and "other" (3%) accounted for the remainder. U.S. inventors hold 49% of multination patents. Japanese inventors have the most total patents filed, but 90% of those patents have not been filed in other countries. The review's findings support that of other studies. In a recent issue of Nanotechnology magazine, a paper by European Commission analysts observed that nanotechnology publishing and patenting is increasing almost proportionately worldwide. Polymer Nanocomposites Toughen Up Polymer nanocomposites—which often include carbon nanotubes—are providing a solution to the growing demand for electrically conductive plastics. A new class of vapor-grown carbon nanotubes and nanofibers gives plastics a wide range of electrical conductivity. They also provide reinforcement and increased thermal conductivity—with only small amounts of these nanoparticles required to impart these characteristics compared to conventional carbon-based additives. For example, Pyrograf Products offers a carbon nanofiber that, at only 0.5-5% of the volume, increases the stiffness of plastics by 500%. Currently, the $50/lb. and up price tags of these nanoparticles are a major drawback. However, the strength and ductility they offer are unsurpassed. Further enhancing the characteristic toughness of polymer nanocomposites may be possible with a new simulation by Dilip Gersappe. Using molecular dynamics simulations, Gersappe was able to delve into how nanoparticles dramatically enhance the toughness of a polymer at different temperatures. He showed that the strength of the nanocomposite could be significantly increased above its glass-transition temperature (Tg) but not below it. Furthermore, this greater toughness above Tg occurs when nanoparticles account for only 10% of the volume—significantly less than standard composites' filler volumes (50%). He also found that the key to increased toughness is mobile nanoparticles, which can obstruct the growth of fractures, even during structural failure. Gersappe notes that super-strong biological materials, like spider silk and abalone shell, whose nanoscale components can dissipate energy, can provide a guide to the fabrication of polymer nanocomposites. Sources: It's Not Just Size that Matters
Sarah Tomlin
Nature, August 1, 2002 "Electrically Active" Compounds Surge in Performance
Robert Leaversuch, Executive Editor
Plastics Technology, June 2002 Patents are Going Down the "Tubes"; Study May Predict Economic Growth
Candace Stuart
Small Times, August 6, 2002 Carbon Nanotubes Found to Fluoresce; Possible Applications in MRI, August 1, 2002 Nanotubes Seen Emitting near-IR Light
Sara Sowah
EE Times, August 6, 2002

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