Distinguishability of particles and its implications for peculiar mass transport in inhomogeneous media

TL;DR

This paper models mass transport in inhomogeneous media, revealing that particle distinguishability and volume exclusion can cause local compression, packet fragmentation, and reversed transport directions, challenging traditional diffusion assumptions.

Contribution

It introduces a model linking particle distinguishability and volume exclusion to peculiar transport phenomena like compression and reversed flow in inhomogeneous media.

Findings

Density relaxation can involve local compression.

Packet front exhibits hopping-like motion and fragmentation.

Mass transport can occur from low to high concentration boundaries.

Abstract

A mass transport directed from low to high density region in an inhomogeneous medium is modeled as a limiting case of a two-component lattice gas with excluded volume constraint and one of the components fixed. In the long-wavelength approximation, density relaxation of mobile particles is governed by a diffusion process and interaction with a medium inhomogeneity represented by a static component distribution. It is shown that density relaxation can be locally accompanied by a density distribution compression. In quasi one-dimensional case, the compression dynamics manifests itself in a hopping-like motion of diffusing substance packet front position due to a staged passing through inhomogeneity barriers and leads to a fragmentation of a packet and retardation of its spreading. A root-mean-square displacement reflects only an averaged packet front dynamics and becomes inappropriate as a transport characteristic in this regime. In a stationary case mass transport throughout a whole system may be directed from a boundary with low concentration towards a boundary with that of high one. Implications of the excluded volume constraint and particles distinguishability for these effects are discussed.