Ribbons, Sheets and the Nanofuture

Posted by Jamais Cascio
August 19, 2005
Source

Unlocking the Code – Science, Systems and Technological Breakthroughs

This is likely the biggest technological breakthrough of the year, arguably even of the decade.

A team of researcher from the University of Texas, Dallas, and Australia's CSIRO has come up with a way to make strong, stable macroscale sheets and ribbons of multiwall nanotubes at a rate of seven meters per minute. These ribbons and sheets, moreover, already display -- without optimization of the process -- important electronic and physical properties, making them suitable for use in an enormous variety of settings, including artificial muscles, transparent antennas, video displays and solar cells -- and many, many more. The breakthrough was announced in the latest edition of Science. As usual, the article itself is behind a subscriber-only wall, but the abstract and supplementary information are available with a free site registration. The press release from UTD (carried by Eurekalert) provides abundant information, however; an article in the UK Guardian gives additional detail.

If you've followed the developments of macro-scale materials made with nanotubes, you'll understand just how enormous a development this is. Previous "sheets" were small and took hours to produce via a liquid-assembly process. This technique allows a meter-long, five centimeter-wide ribbon to be created in seconds. The Science supplemental material page has a link to a video of this in action -- the image above right is a screencap from that video -- and the speed at which the carbon nanotube ribbon is produced is just amazing.

But as startling as the production speed is, it pales in comparison to the material's properties. To start with, the measured gravimetric strength of the nanoribbons -- again, this is the unoptimized version -- already exceeds steel and carbon fiber materials such as Kevlar. Moreover:

The nanotube sheets can be made so thin that a square kilometer of solar sail would weigh only 30 kilograms. While sheets normally have much lower strength than fibers or yarns, the strength of the nanotube sheets in the nanotube alignment direction already approaches the highest reported values for polymer-free nanotube yarns.

The nanotube sheets combine high transparency with high electronic conductivity, are highly flexible and provide giant gravimetric surface areas, which has enabled the team to demonstrate their use as electrodes for bright organic light emitting diodes for displays and as solar cells for light harvesting. Electrodes that can be reversibly deformed over 100 percent without losing electrical conductivity are needed for high stroke artificial muscles, and the Science article describes a simple method that makes this possible for the nanotube sheets.

The solar cell aspect is particularly interesting: imagine being able to roll out flexible solar materials nearly as easily as pulling tape from a roll. And it just gets better:

The use of the nanotube sheets as planar incandescent sources of highly polarized infrared and visible radiation is also reported in the Science article. Since the nanotube sheets strongly absorb microwave radiation, which causes localized heating, the scientists were able to utilize a kitchen microwave oven to weld together plexiglas plates to make a window. Neither the electrical conductivity of the nanotube sheets nor their transparency was affected by the welding process -- which suggests a novel way to imbed these sheets as transparent heating elements and antennas for car windows. The nanotube sheets generate surprisingly low electronic noise and have an exceptionally low dependence of electronic conductivity on temperature. That suggests their possible application as high-quality sensors - which is a very active area of nanotube research.

The nanotube sheets appear to support the healthy growth of cells, suggesting their possible use as scaffolds for tissue growth. Other immediately apparent applications include:

...supercapacitors, batteries, fuel cells and thermal-energy-harvesting cells exploiting giant-surface-area nanotube sheet electrodes; light sources, displays, and X-ray sources that use the nanotube sheets as high-intensity sources of field-emitted electrons; and heat pipes for electronic equipment that exploit the high thermal conductivity of nanotubes. Multifunctional applications like nanotube sheets that simultaneously store energy and provide structural reinforcement for a side panel of an electrically powered vehicle also are promising

Furthermore, this breakthrough puts us enormously closer to the ability to build an Earth-to-orbit elevator. The strength of this ribbon is not yet sufficient for such a purpose, but the required level of strength is no longer a distant prospect.

Although the process is already close to commercial speed and cost, important questions remain to be studied. How scalable is the process -- could nanosheets many meters (or kilometers) across really be produced? More importantly, how stable are the materials over the long-haul? What would cause them to break down? And when they do degrade, how small are the resulting particles? Although solid research into the risks of nanotubes remains to be done, early signs are that some configurations, under some conditions, could be hazardous. If nanotubes are shown to have broader health risks than currently thought, how readily would these nanoribbons degrade into toxic particles?

These questions remain to be answered, and while caution about nanotube toxicity remains warranted, the variety of applications of these nanoribbons and sheets -- in medicine, in energy, in material production and ultra-low-power electronics -- suggests we look very hard at ways for any risks to be mitigated, rather than simply discarding the technology.

This is a no-kidding technological paradigm shift in the making.