Clustering effects on the diffusion of patchy colloids in disordered porous media

TL;DR

This paper extends Enskog theory to describe how patchy colloids diffuse in disordered porous media, accounting for trapping effects and cluster interactions, revealing complex dependencies on fluid density and matrix porosity.

Contribution

The work introduces modified pair distribution functions incorporating probe particle porosity, providing a more accurate theoretical framework for colloid diffusion in porous environments.

Findings

Self-diffusion decreases at low fluid density due to intramolecular correlations.

Depletion effects can increase diffusion at intermediate densities.

High fluid density results in strong diffusion reduction due to hard sphere effects.

Abstract

Enskog theory is extended for the description of the self-diffusion coefficient of patchy colloidal fluid in disordered porous media. The theory includes the contact values of fluid-fluid and fluid-matrix pair distribution functions that are modified to include the dependence from the so-called probe particle porosity, $\phi$, in order to correctly describe the effects of trapping the fluid particles by a matrix. The proposed expressions for the modified contact values of fluid-fluid and fluid-matrix pair distribution functions include three terms. Namely, a hard sphere contribution obtained by us in the previous work [Holovko M. F., Korvatska M. Ya., Condens. Matter Phys., 2020, 23, 23605], the depletion contribution connected with the cluster-cluster and cluster-matrix repulsion and the intramolecular correlation inside the cluster. It is shown that the last term leads to a remarkable decrease of the self-diffusion coefficient at a low fluid density. With a decreasing matrix porosity, this effect becomes weaker. For intermediate fluid densities, the depletion contribution leads to an increase of the self-diffusion coefficient in comparison with the hard sphere fluid. For a sufficiently dense fluid, the self-diffusion coefficient strongly decreases due to a hard sphere effect. The influence of the cluster size and the type of clusters as well as of the parameters of porous media is investigated and discussed in detail.