Insights into Friction in Carbon Nanotubes: Guest-Host Interactions and Temperature-Driven Pinning and Unpinning in Nanopeapods.

We report a complete neutron-scattering and molecular dynamics investigation of the structure and dynamics of monomer and polymer phases of C60 carbon peapods. Above ∼250 K, the physics of the confined chains can fully be described without accounting for the nanotube, the latter merely playing the role of a container for a 1D system─the system can be described as an unpinned state in the extended Frenkel-Kontorova framework. As the temperature is lowered below about 250 K, we observe a progressive damping of the longitudinal acoustic phonons, measured in both monomer and polymer data. As a set of experimental observations suggest that this damping can be attributed neither to a 3D ordering of the chains nor to a transition driven by rotation-rotation-translation coupling, we attribute it to an increase in the chain-nanotube interaction. This translates into a progressive pinning of the C60 chains on the nanotube lattice as the temperature is lowered and explains the observed low-temperature damping.