Potential routes to stronger carbon nanotube fibres via carbon ion irradiation and deposition

Fibres made from carbon nanotubes (CNTs) have not yet achieved strengths approaching that of individual CNTs. The problem is that load is not effectively transferred between the constituent, discontinuous CNTs. High energy irradiation has shown promise on small CNT bundles, in creating covalent crosslinks to enhance load transfer, but cannot sufficiently penetrate real CNT fibres, which typically contain 106 or more CNTs. Here, we suggest that the "draw-twist" process for producing CNT fibres from forests offers an opportunity for CNT bundles to be individually treated with irradiation before being twisted to form a fibre. We use molecular dynamics to examine the effectiveness of low energy (1 eV) carbon ion irradiation (or deposition) in this context. We find that very small amounts of deposition can significantly enhance both intra-bundle and inter-bundle load transfer. Within bundles, deposition atoms mediate covalent links between both the sides and ends of neighbouring CNTs. Inter-bundle load transfer is improved as under-coordinated carbon adatom branches formed during deposition, spontaneously form inter-bundle cross-links as the bundles are forced together by the twisting action. The effects of varying fluence and twisting angles are examined, and the potential to add a prior higher energy irradiation step to penetrate larger bundles is explored. The possibility to produce an amorphous carbon/CNT composite fibre is also discussed. (C) 2015 Elsevier Ltd. All rights reserved.