Developing a new class of lightweight materials with novel functionalities including flexibility and stretchability, allowing for various applications and designs previously impossible with traditional electronics technology, falls under the purview of wearable electronics.
Technological demands on our modern society have generated a strong interest in such materials and a number of research efforts in recent years have shown the possibility of electronics built on flexible and transparent surfaces.
A team from Stanford University has shown that the carbon nanotube-based ‘ink’ that they developed and demonstrated in 2009, can serve as a dye that can provide a simple and inexpensive solution to turning clothing and textiles into energy sources. The fabrics are dipped in the ink of single-walled carbon nanotubes (SWNTs), and this approach was first demonstrated last year on plain copier paper. This new application to fabrics is reported in the journal Nano Letters. The interwoven fibres of fabrics are particularly suitable for absorbing the nanotube ink, maintaining an electrical connection across the whole area of a garment.
In the recent experiments, a cloth is dipped into a batch of nanotube ink dye, and is then pressed to thin and even out the coating. The fabric has been demonstrated to retain its properties even as it is stretched, folded, rinsed in water, or wrung. This exercise has resulted in highly conductive textiles with conductivity of 125 S/cm-1 and sheet resistance less than 1 Ω/sq. The team has also made supercapacitors – conductive textiles that have shown high area capacitance, up to 0,48 F/cm², and high specific energy. The team has also demonstrated the loading of pseudo-capacitor materials into the fabric, and this has resulted in a 24-fold increase of the area capacitance of the device.
In contrast to stretchable conductors reported by others in which the conductivity decreases with stretching, as the SWNT-fabric created by the team is stretched, the conductance increases. Combining low-tech traditional technology such as fabrics and paper with high-tech nanotechnology opens up avenues for new applications. The team looks forward to work on integrated energy storage devices in order to create more useful batteries. The possibility of devising a wearable solar cell is also being pursued, and roll-up displays are another emerging area of interest.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)18 464 2402, [email protected], www.frost.com
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