Effective diffusivities of point-like molecules in isotropic porous media by Monte Carlo simulation

Monte Carlo simulations of point-like molecules in random and structured me dia are used to determine and characterize the effective diffusion coeffici ents of the molecules in the media. Simulations were carried out in 2D and 3D media. Monte Carlo simulation results in 2D and 3D media are compared wi th those obtained by analytical techniques. Simulation results indicate tha t for the structured, isotropic media the effective diffusivities can be ch aracterized according to percolation thresholds in addition to porosity. Th e effective diffusivities in two isotropic media with the same porosity but different percolation thresholds can differ significantly. The effects of dimensionality on the effective diffusivities can also be significant. It i s shown that in general the effective diffusion coefficients obtained from 2D simulation are not a good approximation to those of 3D, especially when the percolation thresholds of the 2D media and the 3D media are very differ ent.