Nanotube structure strengthens flexible electronics

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Thin carbon nanotube (CNT) textiles, synthesised by researchers at the University of Illinois at Urbana-Champaign, exhibit both high electrical conductivity and a level of toughness that is about 50 times higher than copper films currently used in electronics.

“The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including biological and structural health monitoring sensors,” explained assistant professor Sameh Tawfick.

“Aligned carbon nanotube sheets are suitable for a range of applications, spanning the micro- to the macro-scales including MEMS, supercapacitor electrodes, electrical cables, artificial muscles, and multi-functional composites.

“To our knowledge, this is the first study to apply the principles of fracture mechanics to design and to study the toughness of nano-architectured CNT textiles. The theoretical framework of fracture mechanics is shown to be very robust for a variety of linear and non-linear materials.”

According to the research team, it has proven difficult to construct fabrics or films from carbon nanotubes that demonstrate the required properties on centimetre or metre scales. The challenge stems from the difficulty of assembling and weaving CNTs since they are so small, and their geometry hard to control.

“The study of the fracture energy of CNT textiles led us to design these extremely tough films,” stated former graduate student Yue Liang.

Beginning with a catalyst deposited on a silicon oxide substrate, vertically aligned CNTs were synthesised via chemical vapour deposition in the form of parallel lines of 5µm width, 10μm length, and 20 to 60μm heights.

“The staggered catalyst pattern is inspired by the brick and mortar design motif commonly seen in tough natural materials such as bone, nacre and bamboo,” Liang added. “Looking for ways to staple the CNTs together, we tried several mechanical approaches to simultaneously re-orient the nanotubes, before finally using the self-driven capillary forces.”