Lars Heinke and Jörg Kärger 2008 New J. Phys. 10 023035 doi:10.1088/1367-2630/10/2/023035
Lars Heinke1 and Jörg Kärger
Show affiliationsThe use of interference microscopy has enabled the direct observation of transient concentration profiles generated by intracrystalline transport diffusion in nanoporous materials. The thus accessible intracrystalline concentration profiles contain a wealth of information which cannot be deduced by any macroscopic method. In this paper, we illustrate five different ways for determining the concentration-dependent diffusivity in one-dimensional systems and two for the surface permeability. These methods are discussed by application to concentration profiles evolving during the uptake of methanol by the zeolite ferrierite and of methanol by the metal organic framework (MOF) manganese(II) formate. We show that the diffusivity can be calculated most precisely by means of Fick's 1st law. As the circumstances permit, Boltzmann's integration method also yields very precise results. Furthermore, we present a simple procedure that enables the estimation of the influence of the surface barrier on the overall uptake process by plotting the boundary concentration versus the overall uptake.
66.30.Pa Diffusion in nanoscale solids
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
Issue 2 (February 2008)
Received 19 December 2008
Published 22 February 2008
Lars Heinke and Jörg Kärger 2008 New J. Phys. 10 023035
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