Transport in nanoporous materials including MOFs : the applicability of Fick’s laws
Diffusion in nanoporous host-guest systems is often considered to be too complicated to comply with such “simple” relations as Fick’s first and second laws of diffusion. However, we show here that the microscopic techniques of diffusion measurement, notably the pulsed field gradient (PFG) technique of NMR and micro-imaging by interference microscopy (IFM) and IR microscopy (IRM), provide direct experimental evidence of the applicability of Fick’s laws to such systems. This remains true in many situations, even when the detailed mechanism is complex. The limitations of the diffusion model are also discussed with reference to the extensive literature of this subject.
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German Science Foundation (DFG), Fonds der Chemischen Industrie and Alexander von Humboldt Foundation