Diffusion in Pore Networks: Effective Self-Diffusivity and the Concept of Tortuosity

Molecular transport in confined spaces plays a fundamental role in well-established and emerging technologies such as catalysis, gas separation, electrochemical energy storage, and nanofluidics. In all these applications, fluids penetrate the voids of porous materials often having a complex morphology. This demands a deep understanding of how structural variables such as pore size distribution and pore connectivity affect transport in order to design or optimize processes and devices. In previous work from this laboratory, the effect of these structural variables had been studied at infinite dilution. Here, we consider nonvanishing densities and investigate the influence of adsorbate density on the effective diffusivity and tortuosity. At finite densities the transport and self-diffusivity are not equivalent at the single pore level, leading to differing effective diffusion coefficients and tortuosities. The tortuosity has previously been shown to be governed not only by the pore network topology, but als...