On the double criticality of fluids adsorbed in disordered porous media

TL;DR

This paper investigates the complex phase transition behavior of fluids in disordered porous media, revealing conditions for double criticality and explaining recent simulation puzzles through mean-field models.

Contribution

It demonstrates that fluids in heterogeneous porous systems can undergo two distinct phase transitions, depending on the heterogeneity, using simplified lattice gas models.

Findings

Identification of conditions for double phase transitions

Explanation of recent simulation anomalies

Insight into fluid behavior in disordered media

Abstract

The phase transition of a fluid adsorbed in a heterogeneous system is studied with two simple lattice gas models within the framework of a mean-field theory. Despite the different origin of the heterogeneity (spatial variation of binding energy or fluid coordination numbers), the fluid can undergo two phase transitions if the hosting system is sufficiently heterogeneous. It is clearly shown that such a polymorphism in the confined fluid results from the successive condensations in distinct spatial regions of the host. We have found the precise conditions at which one two phase transitions occur. The insight gained from the present study allows one to understand better some recent puzzling simulation results.