Yves Méheust (Université de Rennes) présentera le lundi 9 juillet à 14h, dans la salle des Conseils de l’UFR de Chimie (T32-42, 1er étage, salle 101), un séminaire intitulé :
Vapor transport in clay powders : cationic control of normal vs. anomalous diffusion
Abstract
We study diffusive vapor transport through a synthetic fluorohectorite powder, in which water molecules travel in mesopores between the clay grains but can also intercalate inside the nanoporous grains, making them swell. The intercalation dynamics is known to be controlled by the type of cation ; in this case exchanging the cations from Na+ to Li+ accelerates the intercalation process. By inferring mesoporous humidity profiles from a space-resolved measurement of grain swelling based on X-ray diffraction, and analyzing these profiles in terms of fractional diffusion, we show that exchanging the cations changes mesoporous transport from Fickian to markedly subdiffusive. This behavior results both from a change in the intercalation dynamics, and from the feedback of transport on the medium’s permeability due to grain swelling. An important practical implication is a large difference in the time needed for vapor to permeate a given length of the clay, depending on the type of intercalated cation.
