Tortuosity of hierarchical porous materials: diffusion experiments and random walk simulations

Diffusion experiments, effective medium theory calculations and random walk simulations were carried out on hierarchical porous 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 absence and in presence of the porous medium. This is a well-defined definition that has the advantage to be compa-rable to the ratio of self-diffusion coefficients for the bulk and confined fluid. Such tortuosity can also be compared with the ratio of bulk and effective electrical conductivities. These calculations are applied 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 (Maxwell) which are often invoked to infer tortuosity expressions based on effective mean field theories. The different methods show that the apparent tortuosity versus probe size/pore size ratio display a maximum.(c) 2022 Elsevier Ltd. All rights reserved.