Conducting Elastic Fibers for Artificial Muscles and Electronic Devices

A study at the Dallas based University of Texas shows how scientists have wrapped electrically conducting carbon nanotube sheets around a rubber core to create super elastic fibers. In addition, these fibers conduct electricity and have some special electronic properties as well.

The elasticity of the fibers is phenomenal. They can be more than 14 times longer than their original lengths by stretching and the process is reversible. The fibers regain their initial lengths once the stretching force goes away. While the fibers can extend to 14 times their length, the electrical conductivity steps up by 200 times.

Scientists have conceived of several uses for these fibers. Their high elasticity and conductivity when they stretch could make them ideal for use as minute interconnects in electronic circuits. This could help in upgrading diverse applications like flexible charging cables for mobile devices, robots with longer ranges and trouble-free pacemaker leads.

These fibers are different from conventional fibers in a major aspect. The conductivity of the ordinary fibers falls when they stretch, because of the reduced area of cross section offered to the path of electricity. On the other hand, conductivity of the new fibers increases when stretched.

Dr. Ray Baughman, director of the Nano Tech Institute at Dallas, has authored a paper on the subject. He explains the enhanced elasticity is owing to the buckled structure that develops while the nanotube sheets wrap around the rubber core. Buckles form along the length and circumference of the fibers.

According to Dr. Zunfeng Liu, a research associate in the institute, the two dimensional buckling maintains the alignment of the rubber core and the nanotube. This prevents the resistance of the fibers from rising while they stretch.

Liu reveals that until now, no material has been able to function over so large a range of strain. This feature makes possible the creation of artificial muscles with rotational properties. Dr. Haines, a research associate of the university and a coauthor of the paper said that this aspect of the artificial muscles could be useful for rotating mirrors in optical circuits.

Scientific workers have found several other uses for the nanotube sheaths or elastomers. A particularly valuable device formed from the new material is a fiber capacitor. In this device, a thin coating of rubber covers a core of nanotube fibers. Over this, there is another sheath of nanotube fibers. The inner and outer nanotube layers form the two electrodes, while the rubber core serves as the dielectric.

Nan Jiang is a member of the scientific team working on the project. He demonstrated in the laboratory of the Nanotech Institute the manner of construction of these conductive elastomers in varying sizes, ranging from 150 microns to considerably larger sizes. The width of the rubber core determines the size.

The easy availability and low cost of the rubber cores make it easy for commercialization of the technology. Baughman’s team at the institute has developed a process that aims to convert the carbon nanotubes into large sheets. This could facilitate the fabrication of diverse applications with the elastic conducting fibers.