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Exploration of molecular dynamics during transient sorption of fluids in mesoporous materials

Nature volume 443, pages 965968 (26 October 2006) | Download Citation

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Abstract

In recent years, considerable progress has been made in the development of novel porous materials with controlled architectures and pore sizes in the mesoporous range1,2,3,4. An important feature of these materials is the phenomenon of adsorption hysteresis: for certain ranges of applied pressure, the amount of a molecular species adsorbed by the mesoporous host is higher on desorption than on adsorption, indicating a failure of the system to equilibrate. Although this phenomenon has been known for over a century, the underlying internal dynamics responsible for the hysteresis remain poorly understood5,6,7,8,9. Here we present a combined experimental and theoretical study in which microscopic and macroscopic aspects of the relaxation dynamics associated with hysteresis are quantified by direct measurement and computer simulations of molecular models. Using nuclear magnetic resonance techniques10,11,12,13,14 and Vycor porous glass15,16 as a model mesoporous system, we have explored the relationship between molecular self-diffusion and global uptake dynamics. For states outside the hysteresis region, the relaxation process is found to be essentially diffusive in character; within the hysteresis region, the dynamics slow down dramatically and, at long times, are dominated by activated rearrangement of the adsorbate density within the host material.

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Acknowledgements

Research on this project at the University of Massachusetts was supported by the National Science Foundation. R.V. and J.K. thank the German Science Foundation and the Alexander von Humboldt Foundation for support.

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Affiliations

  1. Abteilung Granzflächenphysik, Fakultät für Physik und Geowissenschaften, Universität Leipzig, D-04103 Leipzig, Germany

    • Rustem Valiullin
    • , Sergej Naumov
    • , Petrik Galvosas
    •  & Jörg Kärger
  2. Department of Chemistry, University of Nevada, Reno, Nevada 89557, USA

    • Hyung-June Woo
  3. Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA

    • Fabien Porcheron
    •  & Peter A. Monson

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Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

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Correspondence to Rustem Valiullin.

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https://doi.org/10.1038/nature05183

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