Orientational melting in carbon nanotube ropes

Using Monte Carlo simulations, we investigate the possibility of an orientational melting transition within a "rope" of carbon nanotubes. When twisting nanotubes bundle up during the synthesis, orientational dislocations or twistons arise from the competition between the anisotropic intertube interactions, which tend to align neighboring tubes, and the torsion rigidity that tends to keep individual tubes straight. We map the energetics of a rope containing twistons onto a lattice gas model and find that the onset of a free "diffusion" of twistons, corresponding to orientational melting, occurs at T-OM greater than or similar to 160 K.