In situ formation of nanotubes by tunnelling

Carbon nanotubes (CNTs) are exquisitely small-diameter cylinders made of rolled graphene, a one-atom-thick sheet of carbon connected in a honeycomb geometry. CNTs can vary in length, thickness and number of layers, but, overall, they are a unique combination of strength, stiffness, and electrical and thermal conductivity.

Applications of CNTs are growing and the possibility to create bulk structures from CNTs such as ropes and mats is expected to have major impact on a number of industries. However, preparation of such bulk CNT-based materials is quite challenging and in its infancy. Scientists working on the EU-funded project 'In-situ fabrication of carbon nanotubes and bulk structures of designed configuration' (CNTBUS) advanced the state of the art.

One promising method under development to produce CNT ropes in situ is by using nanoparticles to tunnel through carbon-rich electrospun polyacrylonitrile (PAN) fibres. PAN is a common acrylic fibre, a synthetic semi-crystalline organic polymer resin. CNTBUS sought to revolutionise this method by incorporating metal nanoparticles in situ to transform the fibres into very high-strength, long-length CNTs.

In particular, the team sought to develop a process whereby metal nanoparticles tunnel inside carbon fibres. Studies exploiting carbon fibres coated with metals suggest that a loose core of the carbon fibres is necessary to guide the movement of the metal nanoparticles. Further, catalysis by the metal nanoparticles appears to cause the stacking of graphene layers to form the CNTs, but the mechanisms for the orderly structuring remain unclear.

Further research exploiting advanced transmission electron microscopy is expected to elucidate the process completely, opening the door to well-controlled synthesis of bulk structures made from CNTs. Such structures are predicted to find widespread use in a variety of applications, including super-reinforcements, filters, masks, catalysers and coatings. European leadership will have major socioeconomic impact.