Transport of water in a weakly-hydrated model clay soil
Abstract
We address the transport of water through a model soil consisting of a looselyaggregated powder of swelling clay (smectite) nano-layered particles. Water has the ability to intercalate stepwise into the nano-porous layered structure of such smectite particles (hence, the term water layers[1]). This makes water transport through the inter-particle clay powder mesoporosity a complex phenomenon, since (i) part of the humidity is trapped in the surrounding particles, and (ii) the particles swell as a result of water intercalation, which leads to a change in the geometry of the mesopores. By imposing a humidity gradient along clay powder samples contained in cylinders and kept at fixed temperature, we have studied quasi-one dimensional water transport in such systems[2,3]. X-ray scattering from the nano-stacks, resolved both in time and in space, provides information on the spatial ingress of the humidity front in the meso-pores, as well as on the amounts of water intercalated in the particle nano-pores. The two interlinked fronts, i.e., humidity (in meso-pores) and intercalation (in nano-pores), have been analyzed together in terms of the classic diffusion scaling variable x/t /2. The result of this analysis suggests near normal diffusive behavior, i.e., an anomalous diffusion exponent close to 1 [4].