Liquid-liquid coexistence in the phase diagram of a fluid confined in fractal porous materials

TL;DR

This study uses advanced simulations to explore the phase diagram of a Lennard-Jones fluid in fractal porous materials, revealing size-dependent effects and complex coexistence phenomena including two distinct liquid phases.

Contribution

It introduces a novel simulation approach to analyze phase behavior of fluids in fractal porous media, highlighting size effects and coexistence of two liquid phases.

Findings

Gas-liquid transition shifted from bulk behavior

Existence of a second liquid-liquid coexistence region

Size effects influence phase diagram results

Abstract

Multicanonical ensemble sampling simulations have been performed to calculate the phase diagram of a Lennard-Jones fluid embedded in a fractal random matrix generated through diffusion limited cluster aggregation. The study of the system at increasing size and constant porosity shows that the results are independent from the matrix realization but not from the size effects. A gas-liquid transition shifted with respect to bulk is found. On growing the size of the system on the high density side of the gas-liquid coexistence curve it appears a second coexistence region between two liquid phases. These two phases are characterized by a different behaviour of the local density inside the interconnected porous structure at the same temperature and chemical potential.