A very interesting article:
Reinforcement of single-walled carbon nanotube bundles by intertube bridging. A=2E Kis1, G. Cs=E1nyi2, J.-P. Salvetat3, Thien-Nga Lee1, E. Couteau1, A. J=2E Kulik1, W. Benoit1, J. Brugger4 & L. Forr=F31 Nature Materials 3, 153 - 157 (2004) Published online: 15 February 2004 | doi:10.1038/nmat1076 "During their production, single-walled carbon nanotubes form bundles. Owing to the weak van der Waals interaction that holds them together in the bundle, the tubes can easily slide on each other, resulting in a shear modulus comparable to that of graphite. This low shear modulus is also a major obstacle in the fabrication of macroscopic fibres composed of carbon nanotubes. Here, we have introduced stable links between neighbouring carbon nanotubes within bundles, using moderate electron-beam irradiation inside a transmission electron microscope. Concurrent measurements of the mechanical properties using an atomic force microscope show a 30-fold increase of the bending modulus, due to the formation of stable crosslinks that effectively eliminate sliding between the nanotubes. Crosslinks were modelled using first- principles calculations, showing that interstitial carbon atoms formed during irradiation in addition to carboxyl groups, can independently lead to bridge formation between neighbouring nanotubes."
News and Views Nanotubes: Strong bundles. Pulickel M. Ajayan1 & Florian Banhart2 Nature Materials 3, 135 - 136 (2004) doi:10.1038/nmat1078 "The mechanical properties of nanotube bundles are limited by the sliding of individual nanotubes across each other. Introducing crosslinks between the nanotubes by electron irradiation prevents sliding, and leads to dramatic improvements in strength."
The researcher team was able to give bundles of nanotubes nearly the same strength in bending modulus as individual nanotubes. Individual nanotubes have a bending modulus of about 1 terapascal. However, nanotubes merely bundled together don't come anywhere near this because the nanotubes slide along each other. The researchers were able to get about 70% of the bending strength of individual nanotubes in their bundles by inducing bonds between the tubes by electron irradiation. Could this work to produce nanotubes of arbitrarily long lengths at nearly the same tensile strength of individual tubes by using the electron radiation method to induce bonds between the ends of nanotubes?
Bob Clark