The curvature effect on the distribution behavior of nonpolar atoms in nano-confined space

Abstract

The chemical and physical properties of nonpolar atoms are obviously affected by confinement. A curvature-based theoretical model for helium particles distributed in carbon nanotubes is proposed by considering the L-J pair potential and the Boltzmann distribution. The potential gap formed by the non-bonded interaction between a helium atom and a carbon nanotube surface leads to a layered structure distribution with high density near the surface. By assuming adsorption as a competition between the potential gap and the thermal energy, the desorption critical temperature is discussed for helium adsorbed on the layer, which is confirmed to be a monotonic decreasing function of nanotube diameter. The helium atom distribution relations between the nanotube diameter, temperature and the potential gap obtained from molecular dynamics simulations are consistent with the curvature-based model predictions. The adsorption ratio is defined by the numbers of particles adsorbed on the near surface layered structure over total particle numbers, which decreases with the increase of temperature and carbon nanotube diameter. The curvature-based model is further confirmed by studying krypton and argon atoms in the appendix. This work provides a simple model to predict the distribution behavior and reveals the curvature effect on the distribution and adsorption of non-polar atoms confined in nano-space, which could be important for a better understanding of the chemical and physical properties of gas storage in the nano-confined space.