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2 mai 2019: 1 événement


  • Séminaires Internes

    Jeudi 2 mai 11:00-12:00 - Alexander Schlaich

    [INTERNE] Coupling of Adsorption and Transport in Hierarchical Porous Materials

    Résumé : Hierarchical porous materials are widely used for adsorption, separation, catalysis etc. as they combine several porosity scales to overcome slow diffusion in their nanoporosity while maintaining a large specific surface area. Fluids in such multiscale confinement exhibit rich thermodynamic and dynamical behaviors that are significantly different from their bulk counterpart : surface forces and reduced dimensions affect phase transitions due to capillary condensation, freezing, etc. and transport in such nanoporous media exhibits a broad range of novel phenomena. As a result, while adsorption and transport in a nanopore is reasonably well understood in the limiting case of liquid filled pores, the complex interplay between thermodynamics and dynamics still lacks satisfactory description for multiscale porous media such as hierarchical porous solids.
    In this work, we discuss in detail the role of the shift in the liquid/vapor coexistence lines due to confinement. Atom-scale simulations were coupled to a multiscale lattice model to obtain explicit descriptions for the coupling between macroscopic transport and the thermodynamics of the confined fluid. By investigating the role of pore size, pressure, temperature and surface chemistry, we are able to sketch a ‘transport phase diagram’. More in details, the microscopic behaviors obtained at the molecular scale allow us to construct a hierarchical lattice model with transport coefficients explicitly derived from Statistical Mechanics. We address how macroscopic transport arises from contributions where gas and liquid phases contribute. Experimental adsorption and dynamical measurements at different scales (from the nm to the micron scales) can readily be included in our model. Successive upscaling allows us to predict the macroscopic transport in hierachical porous materials from simple experimental topological data as obtained from tomography, electron microscopy, etc. We demonstrate that our simple approach can be employed to optimize the adsorption and transport of fluids confined in multiscale porous solids.

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