The bulk viscosity of a symmetrical Lennard--Jones mixture above and at liquid--liquid coexistence: A computer simulation study

TL;DR

This study uses computer simulations to analyze the bulk viscosity and other properties of a symmetrical Lennard-Jones binary mixture near its liquid-liquid coexistence, revealing critical behavior and property variations.

Contribution

It provides detailed simulation data on static and dynamic properties of a Lennard-Jones mixture near coexistence, including phase diagram and viscosity behavior.

Findings

Bulk viscosity increases significantly near coexistence.

Isothermal compressibility and concentration susceptibility grow near the critical point.

Shear viscosity shows weak temperature dependence.

Abstract

A Lennard--Jones model of a binary dense liquid (A,B) with a symmetrical miscibility gap is investigated by means of computer simulation methods. Semigrand--canonical Monte Carlo simulations yield the phase diagram in the $T$--$x$ plane ($T$: temperature, $x$: concentration of A or B particles) as well as equilibrated configurations at coexistence. Then Molecular Dynamics simulations use these configurations to determine static properties (isothermal compressibility $\kappa_T$ and concentration susceptibility $\chi$) as well as the shear and the bulk viscosity $\eta_{\rm s}$ and $\eta_{\rm B}$, respectively. The latter quantities are calculated along a path approaching the coexistence line from high temperatures in the one--phase region and ending at a state at the coexistence line about 15% below the critical point. We find that $\kappa_T$ and $\chi$ increase significantly near the coexistence line reflecting the vicinity of the critical point. Whereas $\eta_{\rm s}$ exhibits a weak temperature dependence, $\eta_{\rm B}$ increases significantly near the coexistence curve.