Accueil du site > Productions scientifiques > Séminaires à PHENIX > 2011 > Séminaire 09.02.2011 - 14h30
par
, - 18 janvier 2011
Pierre Levitz du laboratoire Physique de la Matière Condensée présentera un séminaire le 9 février 2011 à 14h30 (1er étage, bâtiment F, porte 113) intitulé :
Multiscale dynamics of confined fluid in colloidal and porous media
Porous materials, concentrated colloidal suspensions are example of confining systems developing large specific surface, presenting a rich variety of shapes and exhibiting complex and irregular morphologies on a large length‐scale. Such a confinement strongly influences the molecular dynamics of embedded fluids. Two distinct and successive confined dynamics are generally considered in such systems : first, the fluid dynamics near the interface, second, the long range exploration of the pore network.
A coarse grain picture of the fluid dynamics near a surface can be considered as an intermittence of adsorption steps and bulk relocations from one point to another point of the interface. Adsorption statistics such as the adsorption time distribution and its first moment reflect the degree of interaction of the molecule with the colloidal interface. The relocation statistics strongly depends on the shape of the colloidal particle, the surface forces and the bulk confinement. In the first part of this talk, we analyze some properties of this intermittent dynamics (ID) for various colloidal interfacial geometries [1] [2]. Direct comparisons with recent Molecular Dynamics simulations [3] are performed in relation with the nature of the geometrical confinement and the degree of interaction between the fluid and the interface. We also present an experimental study of the ID, using NMR relaxometry, for various porous solids or colloidal systems (Vycor glass [4], plaster pastes [5], flat colloidal clay particles [6], long and stiff nanometric strands [7]).
Large iteration of the intermittent dynamics allows exploring the long range organization of the colloidal and/or porous matrix. However, most of natural or manufactured porous materials develop a complex hierarchical structure. It is then important to characterize in parallel the geometrical and the transport properties in the intermediate length scales, filling the gap from nano to micro scales. In this respect, we present some recent 3D structural analysis using imaging techniques [8] such as X rays microtomography, or X rays microscopy and carried out on various hierarchical colloidal systems or pore network. We use these 3D experimental configurations and a generalization of the intermittent dynamics to analyze the molecular exchange dynamics between different levels of pore organization. Comparison with experimental data from T2‐T2 correlation spectroscopy is then provided.
[1] P. Levitz, Random flights in confining interfacial systems, J. Phys. Condens. Matt. 17, S4059 (2005)
[2] P. Levitz, D. S. Grebenkov, M. Zinsmeister, K. Kolwankar, B. Sapoval, Brownian flights over a fractal nest and first‐passage statistics on irregular surfaces, Phys. Rev. Lett. 96, 180601 (2006).
[3] P. A. Bonnaud, B. Coasne and R. J.‐M. Pellenq, Molecular simulation of water confined in nanoporous silica J. Phys. Condens. Matt 22 , 284110 (2010)
[4] P. Levitz , J.-P. Korb, D. Petit, Slow dynamics of embedded fluid in mesoscopic confining systems as probed by NMR relaxometry European Physical Journal E 12, 29 (2003)
[5] J.‐P. Korb , P Levitz, Direct Probing of the Wettability of Plaster Pastes at the Nanoscale by Proton Field Cycling Relaxometry, Magnetic Resonance in Porous Media 1081, 55‐58 (2008)
[6] P. E. Levitz, J.‐P. Korb, Probing glass transition of clay colloids by NMR relaxometry : Interplay between fluid Brownian dynamics and particle jamming Europhysics Letters 70, 684 (2005)
[7] P. Levitz, M. Zinsmeister, P. Davidson, D. Constantin, O. Poncelet, Intermittent Brownian dynamics over a rigid strand : Heavily tailed relocation statistics in a simple geometry, Phys. Rev. E 78, 030102 (R) (2008).
[8] M. Han, S. Youssef, E. Rosenberg, M. Fleury, P. Levitz, Deviation from Archie’s law in partially saturated porous media : Wetting film versus disconnectedness of the conducting phase, Phys. Rev. E 79, 031127 (2009)
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