Electric cotton — the rise of smart clothing

A March 5, 2009 article in the Economist's Technology Quarterly supplement featured recent work by Nicholas Kotov's group at the University of Michigan.

They've succeeded in combining cotton with carbon nanotubes to create light, easily woven fabrics that can conduct electricity.

Above and below, the hybrid tubes.

Here's the article.

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A Good Yarn

Nanotechnology: Cotton fibres coated with carbon nanotubes could be used to make clothing that glows, or detects bleeding

Many science-fiction stories portray a time when warring generals monitor their forces on computer displays that are linked to special suits worn by their soldiers. Information about any injuries are sent to the command station immediately, so the generals can tell that, say, Sergeant Johnson has a fractured ankle or that Corporal Caley has lost 1.2 litres of blood. Such a day may not be too far off. Researchers have been able to produce cotton fibres capable of detecting blood and of signalling its presence electrically.

Intelligent textiles have a lot of appeal. For both soldiers and doctors, clothing that adapts to changing conditions could provide adjustable levels of protection from such things as microbes, chemicals and radiation. Commercial manufacturers see huge potential in clothes that glow, do not wrinkle or overcome body odour. Materials can already be made to do some of these things, but they are too bulky, rigid or complicated for practical use. So the aim is to manufacture a light material that can be easily woven but is also highly durable and, in order to transmit information, can conduct electricity.

A team of researchers led by Nicholas Kotov, a chemical engineer at the University of Michigan, has come up with a way in which this might be done by coating cotton threads with carbon nanotubes. These tubes are cylindrical carbon molecules with a unique honeycomb-like arrangement of atoms. They are regarded as among the most versatile nanomaterials available because of their mechanical strength and electrical properties.

Nanotube composites are often made into solid structures or sheets, although flexible versions, such as electrically conductive films and electronic inks, can be prepared from dilute nanotube solutions. Some electronic devices, such as field-emission displays in some flat panels, are made from nanotube yarns. But the weaving of these yarns, which may be only one-thousandth of a millimetre thick, is complicated and expensive. Creating garments with electrical properties has not been considered practical.

However, Dr Kotov and his colleagues have reported in Nano Letters a simple process for coating standard cotton threads with carbon nanotubes. Being much thicker than nanotube yarns, such threads can be woven more easily. The researchers dispersed carbon nanotubes in a dilute solution of a mixture of Nafion, a commercial synthetic polymer, and ethanol. They then repeatedly dipped cotton threads, 1.5mm in diameter, into the solution, letting them dry between each dip. This allowed the nanotubes to cover individual cotton strands and to adhere strongly to the surface of the cellulose fibres in the strands. The process also encouraged the nanotubes to arrange themselves along the axis of the cotton fibres, which increased electrical connectivity. After several dips, Dr Kotov found that the cotton threads were conductive enough that they could be used to wire up a light-emitting diode.

In a further test the researchers added molecules of a material that reacts with human serum albumin, an essential component of human blood, to the dipping solution. Then they immersed more cotton threads. This time they ran an electrical current through the thread while exposing it to different concentrations of albumin. They found that the threads’ electrical conductivity varied according to the level of albumin. The researchers propose that such material could be used to detect bleeding if suitably woven into military clothing—just as the science-fiction writers predicted.

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Here's a link to the abstract of Kotov's November 7, 2008 report in Nano Letters; the abstract itself follows.

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Smart Electronic Yarns and Wearable Fabrics for Human Biomonitoring made by Carbon Nanotube Coating with Polyelectrolytes

The idea of electronic yarns and textiles has appeared for quite some time, but their properties often do not meet practical expectations. In addition to chemical/mechanical durability and high electrical conductivity, important materials qualifications include weavablity, wearability, light weight, and “smart” functionalities. Here we demonstrate a simple process of transforming general commodity cotton threads into intelligent e-textiles using a polyelectrolyte-based coating with carbon nanotubes (CNTs). Efficient charge transport through the network of nanotubes (20 Ω/cm) and the possibility to engineer tunneling junctions make them promising materials for many high-knowledge-content garments. Along with integrated humidity sensing, we demonstrate that CNT−cotton threads can be used to detect albumin, the key protein of blood, with high sensitivity and selectivity. Notwithstanding future challenges, these proof-of-concept demonstrations provide a direct pathway for the application of these materials as wearable biomonitoring and telemedicine sensors, which are simple, sensitive, selective, and versatile.

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A December 12, 2008 Scientific American article has more.

Below,

a plain piece of cotton along with nanotube-coated swatches.