Explicit spatial description of fluid inclusions in porous matrices in terms of an inhomogeneous integral equation

TL;DR

This paper develops an integral equation approach to explicitly describe the spatial distribution of fluids, including Lennard-Jones and SALR particles, within a porous medium, revealing distinct aggregation behaviors and matching simulation results.

Contribution

It introduces a two-dimensional Ornstein-Zernike method combined with a Replica approach to accurately predict fluid spatial distributions in porous matrices, highlighting differences between LJ and SALR fluids.

Findings

SALR particles form clusters in pores, unlike LJ fluids which wet walls uniformly.

The integral equation approach accurately predicts fluid distributions compared to Molecular Dynamics.

The method effectively captures the influence of pore structure on fluid behavior.

Abstract

We study the fluid inclusion of both Lennard-Jones particles and particles with competing interaction ranges --short range attractive and long range repulsive (SALR)-- in a disordered porous medium constructed as a controlled pore glass in two dimensions. With the aid of a full two-dimensional Ornstein-Zernike approach, complemented by a Replica Ornstein-Zernike integral equation, we explicitly obtain the spatial density distribution of the fluid adsorbed in the porous matrix and a good approximation for the average fluid-matrix correlations. The results illustrate the remarkable differences between the adsorbed Lennard-Jones (LJ) and SALR systems. In the latter instance, particles tend to aggregate in clusters which occupy pockets and bays in the porous structure, whereas the LJ fluid uniformly wets the porous walls. A comparison with Molecular Dynamics simulations shows that the two-dimensional Ornstein-Zernike approach with a Hypernetted Chain closure together with a sensible approximation for the fluid-fluid correlations can provide an accurate picture of the spatial distribution of adsorbed fluids for a given configuration of porous material.