Dimensional crossover and quantum effects of gases adsorbed on nanotube bundles

Adsorption properties of several gases (Ne, CH₄, Ar, and Xe) on the external surface of a carbon nanotube bundle are investigated. Calculations are performed at low coverage and variable temperature, and for some fixed temperatures as a function of coverage. Within a simple model (in the limit of very low coverage) we are able to study the evolution of the film's thermal properties from those of a one dimensional (1D) fluid to those of a 2D film. In addition, grand canonical Monte Carlo simulations are performed in order to identify a second-layer groove phase that occurs once a monolayer of atoms covers the external surface. We derive from the simulations the isosteric heat, compressibility, and specific heat as a function of coverage. We evaluate alternative models in order to derive quantum corrections to the classical results. We compare our findings with those of recent adsorption experiments.