 The effective diffusivity of species "A" in a binary mixture of "A" and "B", formula_25 is determined by

where formula_27
For cases where α = 0 (formula_28) or where formula_29 is close to zero, the equation reduces to

In the Knudsen diffusion regime, the molecules do not interact with one another, so that they move in straight lines between points on the pore channel surface.Self-diffusivity is a measure of the translational mobility of individual molecules.Under conditions of thermodynamic equilibrium, a molecule is tagged and its trajectory followed over a long time.