Transport properties of nitrogen in single walled carbon nanotubes

Abstract

Transport properties including collective and tracer diffusivities of nitrogen, modeled as a diatomic molecule, in single walled carbon nanotubes have been studied by equilibrium molecular dynamics at different temperatures and as a function of pressure. It is shown that while the asymptotic decay of the translational and rotational velocity autocorrelation function is algebraic, the collective velocity decays exponentially with the relaxation time related to the interfacial friction. The tracer diffusivity in the nanochannel, which is comparable in magnitude with diffusivity in the equilibrium bulk phase, depends only weakly on the conditions at the fluid–solid interface, whereas the collective diffusivity is a strong function of the hydrodynamic boundary conditions and is found to be three orders of magnitude higher than self-diffusivity in carbon nanotubes and for the comparatively rough surface of the rare-gas tube it is one order of magnitude greater. A relationship between the collective diffusivity and the Maxwell coefficient describing wall collisions is obtained. The transport coefficients appear to be insensitive to the long-range details of the potential function.