Dynamics and phase transitions under spatial confirnements
Chemical and Thermal Process Engineering
Final Report Abstract
Recent progress in the chemical synthesis of mesoporous solids has boosted the area of their potential applications both in technological processes and fundamental research. Transport of molecular species confined to such materials often plays a decisive role in the evolution of many physicochemical processes occurring in pore spaces. This project was devoted to the experimental study of two different transport modes, which have major impacts on mass transfer in mesoporous solids. In the first part of the project, molecular microscopic translational dynamics under (quasi)equilibrium conditions, i.e. self-diffusion, was addressed. A comprehensive pulsed field gradient NMR study of diffusion properties of confined species in a broad range of phase coexistences, including gas-liquid, solid-liquid and near-critical conditions, was performed. By considering the elementary steps of different diffusion mechanisms which are effective in different regions of the coexistence phase diagram, it is shown that the molecular diffusivities can very accurately be predicted on the basis of the known phase state. As a particular point, special attention has been paid to understand the role of structural disorder upon the fluid properties and to develop approaches to quantify structural disorder in mesoporous solids. The second part was devoted to non-equilibrium macroscopic transport in response to a variation of the external parameters, such as chemical potential. It is demonstrated that such variations are accompanied by extremely slow relaxation dynamics, which can directly be associated with slow phase growth under confinement. This was observed over a large spectrum of porous solids with different pore morphologies and the microscopic mechanisms leading to slow dynamics were rationalized by mapping the phenomenon onto the classical problem of particle motion in a random potential field, resulting from the structural disorder of the pore spaces.
Publications
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Pulsed field gradient NMR study of surface diffusion in mesoporous adsorbents. Microporous Mesoporous Mat. 2009, 125 (1-2), 58-62
Dvoyashkin, M.; Khokhlov, A.; Naumov, S.; Valiullin, R.
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Understanding adsorption and desorption processes in mesoporous materials with independent disordered channels. Phys. Rev. E 2009, 80 (3), 031607
Naumov, S.; Valiullin, R.; Kärger, J.; Monson, P. A.
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Probing pore connectivity in random porous materials by scanning freezing and melting experiments. Langmuir 2010, 26 (9), 6380-6385
Kondrashova, D.; Reichenbach, C.; Valiullin, R.
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Structural characterization of porous solids by simultaneously monitoring the low-temperature phase equilibria and diffusion of intrapore fluids using nuclear magnetic resonance. New J. Phys. 2011, 13 (1), 015008
Kondrashova, D.; Dvoyashkin, M.; Valiullin, R.
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Diffusion in Hierarchical Mesoporous Materials: Applicability and Generalization of the Fast-Exchange Diffusion Model. Langmuir 2012, 28 (7), 3621-3632
Zeigermann, P.; Naumov, S.; Mascotto, S.; Kärger, J.; Smarsly, B. M.; Valiullin, R.
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Diffusion in Nanoporous Host Systems. Annual Reports on NMR Spectroscopy 2013, 79, 23-72
Valiullin, R.
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Improving structural analysis of disordered mesoporous materials using NMR cryoporometry. Microporous Mesoporous Mat. 2013, 178 (0), 15-19
Kondrashova, D.; Valiullin, R.
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Mass Transfer in Mesoporous Materials: The Benefit of Microscopic Diffusion Measurement. Chem. Soc. Rev. 2013, 42 (9), 4172 - 4197
Kärger, J.; Valiullin, R.
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Transport Properties of Gas-Expanded Liquids in Bulk and under Confinement. J. Supercrit. Fluid. 2013, 75, 43-47
Zeigermann, P.; Valiullin, R.
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Filling Dynamics of Closed End Nanocapillaries. Langmuir 2014, 30 (5), 1290-1294
Schneider, D.; Valiullin, R.; Monson, P. A.
