The use of interference microscopy permitted the direct observation of transient concentration profiles generated by intracrystalline transport diffusion in nanoporous materials. These accessible intracrystalline concentration profiles contained a wealth of information which could not be deduced using any macroscopic method. Here, 5 different ways were illustrated for determining the concentration-dependent diffusivity in 1-dimensional systems, plus two methods for the surface permeability. These methods were considered with regard to their application to concentration profiles evolving during the uptake of methanol by the zeolite ferrierite and of methanol by the metal organic framework manganese(II) formate. It was shown that the diffusivity could be calculated most precisely by means of Fick's 1st law. When possible, Boltzmann's integration method also yielded very precise results. A simple procedure was presented that permitted an estimation of the influence of the surface barrier upon the overall uptake process by plotting the boundary concentration versus the overall uptake.

Assessing One-Dimensional Diffusion in Nanoporous Materials from Transient Concentration Profiles. L.Heinke, J.Kärger: New Journal of Physics, 2008, 10[2], 023035 (25pp)