Modeling Gaseous Diffusion in Nanopores*

A phenomenological theory for gaseous diffusion within nanopores is presented where the flux is given in terms of a probability distribution for scattering path lengths. Using a simple molecular dynamics simulation a model distribution is developed and a Fickian diffusion coefficient determined. This is done for various simple gases within a membrane pore. Diffusion coefficients are computed in each case over a selected temperature range and compared with experimental values when possible. The diffusion is explained in terms of Knudsen and surface effects. This theory is also compared with other prominent theories from the literature used to describe this phenomenon.