Feb 2, 2010
Laser-etched CNT array delivers uniform yarn
Carbon nanotube (CNT) yarns can be made from super-aligned carbon nanotube arrays by a spinning method that combines twisting and shrinking processes. The yarns have high tensile strengths up to 1 GPa and are available in a wide range of diameters from several to tens of micrometers. The spinning process is continuous, which makes it easy to produce long yarns. Samples measure from tens to hundreds of metres in length.
It is an amazing discovery that CNTs can be directly drawn out in a dry state from so-called super-aligned CNT (SACNT) arrays. Up until now, there have been two methods to make these drawn-out CNTs into a yarn: twisting CNTs by down-sizing an industrial twisting process and shrinking CNTs using some solvents, but the two separate methods have some disadvantages for making uniform and high-strength yarns.
Recently, researchers at Tsinghua University have developed a simple and continuous method that combines the twisting and shrinking processes to make high-strength CNT yarns. In this method, a yarn freshly spun from a SACNT array is first twisted and then passed through a solvent for shrinking. The two processes deliver a yarn that consists of densely packed CNTs and has a tensile strength of more than 1 GPa. The tensile strength depends on the diameter and the twisting angle of the yarn, and peaks at a yarn diameter around 10 µm. Different kinds of solvents, such as water, ethanol and acetone, have used to shrink the twisted yarns, with acetone showing the best shrinking effect.
The team uses a laser scanning method to parallel etch its SACNT array, which ensures that the CNT yarn is produced with a uniform diameter. By this method, CNT yarns with a wide diameter range can be obtained: the thinnest is about 4 µm and the thickest can reach up to 40 µm in diameter.
The CNT yarns are conductive (Rs ~ 1.1 × 10–5 Ω m) and much stronger and lighter than thin metal wires. These advantages make CNT yarns superior materials for use as high-strength and ultra-thin conducting wires with a diameter less than 10 µm.
Full results are available in the journal Nanotechnology.
About the author
Dr Kai Liu and Dr Yinghui Sun are both postdoctoral research associates at Tsinghua-Foxconn Nanotechnology Research Center. They are studying the properties and applications of carbon nanotube films and yarns. Ruifeng Zhou is a graduate student and Hanyu Zhu is an undergraduate student in the Department of Physics at Tsinghua University. Prof. Jiaping Wang is an associate professor of physics at Tsinghua University, whose research field is CNT-based composite materials and lithium ion batteries. Dr Liang Liu is a research scientist at Tsinghua-Foxconn Nanotechnology Research Center. Prof. Kaili Jiang is a professor of physics at Tsinghua University, whose research interests include the synthesis, properties and applications of super-aligned carbon nanotubes. Prof. Shoushan Fan is a professor of physics at Tsinghua University and the director of Tsinghua-Foxconn Nanotechnology Research Center.