Global phase diagrams of binary dipolar fluid mixtures

TL;DR

This paper uses a modified mean-field density functional theory to map the complex phase diagrams of binary dipolar fluid mixtures, revealing various phase transitions and how they change with dipole strength and particle size.

Contribution

It provides the first comprehensive global phase diagrams of binary Stockmayer fluids in three-dimensional thermodynamic space, including detailed analysis of phase transition lines and their topology.

Findings

Identified vapor-liquid, liquid-liquid, and magnetic phase separations.

Calculated second-order transition loci using Landau theory.

Mapped critical, tricritical, and triple lines in phase diagrams.

Abstract

We apply a modified mean-field density functional theory to determine the phase behavior of binary mixtures of Stockmayer fluids whose spherical constituents interact according to Lennard-Jones (LJ) pair potentials with embedded pointlike dipole moments. On the basis of systematic numerical calculations we construct the global phase diagrams of these systems in the three-dimensional thermodynamic space of temperature, pressure, and chemical potential difference of the two components. The vapor-liquid, isotropic liquid - isotropic liquid, isotropic liquid - ferromagnetic liquid, and ferromagnetic liquid - ferromagnetic liquid first-order phase separations are investigated. The loci of the second-order isotropic fluid - ferromagnetic fluid transition are calculated from Landau theory. Liquid-vapor and liquid-liquid critical lines, tricritical lines, triple lines, and lines of critical end points of the binary Stockmayer mixtures are also determined. We discuss how the topology of the phase diagrams change upon varying the strengths of the two dipole moments of the two species as well as their sizes.