Rounding of the localization transition in model porous media

TL;DR

This study uses computer simulations of two-dimensional porous media models to explore how the localization transition becomes rounded in realistic systems with soft potentials, revealing the impact on anomalous transport and diffusion.

Contribution

It demonstrates that the rounding of the localization transition is a generic feature in soft-potential porous media models, bridging idealized and realistic systems.

Findings

Anomalous transport persists over decades in time.

Self-diffusion decreases with increasing density.

Transition rounding occurs due to energy-dependent critical densities.

Abstract

The generic mechanisms of anomalous transport in porous media are investigated by computer simulations of two-dimensional model systems. In order to bridge the gap between the strongly idealized Lorentz model and realistic models of porous media, two models of increasing complexity are considered: a cherry-pit model with hard-core correlations as well as a soft-potential model. An ideal gas of tracer particles inserted into these structures is found to exhibit anomalous transport which extends up to several decades in time. Also, the self-diffusion of the tracers becomes suppressed upon increasing the density of the systems. These phenomena are attributed to an underlying percolation transition. In the soft potential model the transition is rounded, since each tracer encounters its own critical density according to its energy. Therefore, the rounding of the transition is a generic occurrence in realistic, soft systems.