Diffusion hysteresis in mesoporous materials
University of Leipzig, Department of Interface Physics, Leipzig, Germany
2 University of Massachusetts, Department of Chemical Engineering, Amherst, Massachusetts, 01003-9303, U.S.A.
The pulsed field gradient NMR method has been used to study molecular diffusion of adsorbate molecules in mesoporous materials with different pore morphologies as a function of the external gas pressure. The obtained experimental results reveal that in line with the adsorption hysteresis, the measured diffusivities as well exhibit a history-dependent behavior, i.e. diffusivities on the adsorption branch do not follow those measured on the desorption branch. Particular details of the diffusion hysteresis loop depend on the structure of the used porous material. New insight into the mechanisms of adsorption hysteresis, namely indication of two-step relaxation process in the hysteresis region, is gained by comparing the dynamical properties of the adsorbate obtained under equilibrium and non-equilibrium conditions.
© EDP Sciences, Springer-Verlag, 2007