Types of dependence of self-diffusivity on sorbate concentration in parameter space: a two-dimensional lattice gas study

Abstract

The various factors that influence the dependence of self-diffusivity D on sorbate concentration c has been investigated by means of lattice gas model. Among the parameters varied are the activation energy, the temperature, the number of adsorption sites, and the pattern of adsorption sites. It is shown that the five types of D vs c dependence observed by Karger and Pfeifer based on the PFG-NMR experiments on a variety of guest-zeolite systems can be understood in terms of the variation of just a few parameters. A self-diffusivity type diagram showing under what conditions a given type is found has been constructed. It is shown that even the approximate lattice gas treatment can reasonably predict the D vs c behavior of a number of guest-zeolite systems besides giving insight into why a particular behavior is observed.