Deformations and thermal stability of carbon nanotube ropes

Structural and thermal characteristics of crystalline ropes of single-wall carbon nanotubes (SWCNTs) are investigated. Novel crystalline ropes of polygonized SWCNTs produced by laser irradiation exhibit rounded-hexagonal cross sections in contrast to earlier observations of circular tubes. Extensive molecular dynamics (MD) simulations lead to several metastable structures of the lattice characterized by different tube cross sections, hexagonal, rounded-hexagonal and circular, and increasing cell volume. The competition between different tube shapes is analyzed and compared to experiments. On the other hand, bundles of SWCNTs coalesce, forming multiwall carbon nanotubes under thermal treatment at high temperatures. Extensive MD simulations confirm the single-wall-to-multiwall transformation and suggest the physical patching-and-tearing mechanism underlying the concerted coalescence of the tubes.