Bridging molecular and continuous descriptions: the case of dynamics in clays

Jean-François Dufrêche, Benjamin Rotenberg, Virginie Marry, Pierre Turq
2010 Anais da Academia Brasileira de Ciências  
The theory of transport in porous media such as clays depends on the level of description. On the macroscopic scale,hydrodynamics equations are used. These continuous descriptions are convenient to model the fluid motion in a confined system. Nevertheless, they are valid only if the pores of the material are much larger than the molecular size of the components of the system. Another approach consists in using molecular descriptions. These two methods which correspond to different levels of
more » ... ription are complementary. The link between them can be clarified by using a coarse-graining procedure where the microscopic laws are averaged over fast variables to get the long time macroscopic laws. We present such an approach in the case of clays. Firstly, we detail the various levels of description and the relations among them, by emphasizing the validity domain of the hydrodynamic equations. Secondly, we focus on the case of dehydrated clays where hydrodynamics is not relevant. We show that it is possible to derive a simple model for the motion of the cesium ion based on the difference on time scale between the solvent and the solute particles.
doi:10.1590/s0001-37652010000100006 pmid:20209243 fatcat:nrp2t6mvknbmtje7vqazhqf6ay