Population inversion of a NAHS mixture adsorbed into a cylindrical pore

TL;DR

This study investigates how a non-additive hard sphere binary fluid behaves inside a cylindrical nanopore, revealing an abrupt population inversion and entropy-driven prewetting transition influenced by various parameters.

Contribution

It introduces the first analysis of population inversion phenomena in a NAHS mixture within a cylindrical pore using integral equations and Monte Carlo simulations.

Findings

Population inversion occurs at higher bulk densities.

Prewetting transition is entropy-driven and occurs at the pore surface.

Phenomena depend on pore size, non-additivity, and particle ratios.

Abstract

A cylindrical nanopore immersed in a non-additive hard sphere binary fluid is studied by means of integral equation theories and Monte Carlo simulations. It is found that at low and intermediate values of the bulk total number density the more concentrated bulk species is preferentially absorbed by the pore, as expected. However, further increments of the bulk number density lead to an abrupt population inversion in the confined fluid and an entropy driven prewetting transition at the outside wall of the pore. These phenomena are a function of the pore size, the non-additivity parameter, the bulk number density, and particles relative number fraction. We discuss our results in relation to the phase separation in the bulk.