Transport of hierarchical porous materials: Diffusion experiments and random walk simulations

International audienceWe carry out random walk simulations on prototypical porous structures that are representative of actual hierarchical silica-based materials. The main throughput of the mesoscopic simulations proposed here is the tortuosity defined as the ratio of the fluid mean square displacements calculated in the absence and in the presence of the porous medium. This is a rigorous mathematical definition that has the advantage to be comparable to the ratio of self-diffusion coefficients for the bulk and confined fluid, which can be directly determined by means of diffusion experiments. Such tortuosity can also be compared with the ratio of bulk and effective electrical conductivities. These calculations are applied here to hierarchical materials such as those encountered in chromatography, membrane science or catalysis. The simulation results are compared to experimental data as well as to effective equations-such as Maxwell's equation-which are often invoked to infer tortuosity expressions based on effective mean field theories