Transport properties of Lennard-Jones fluids: Freezing density scaling along isotherms

TL;DR

This study shows that reduced transport coefficients of Lennard-Jones fluids along isotherms follow a quasi-universal density scaling related to hard-sphere fluids, with the Stokes-Einstein relation valid in dense regimes.

Contribution

It introduces a density scaling law for transport properties of Lennard-Jones fluids along isotherms and links it to hard-sphere fluid behavior, providing practical demarcation of fluid regimes.

Findings

Transport coefficients scale with density at freezing point

Stokes-Einstein relation holds without hydrodynamic diameter in dense fluids

Lower density boundary marks gas-like and liquid-like regimes

Abstract

It is demonstrated that properly reduced transport coefficients (self-diffusion, shear viscosity, and thermal conductivity) of Lennard-Jones fluids along isotherms exhibit quasi-universal scaling on the density divided by its value at the freezing point. Moreover, this scaling is closely related to the density scaling of transport coefficients of hard-sphere fluids. The Stokes-Einstein relation without the hydrodynamic diameter is valid in the dense fluid regime. The lower density boundary of its validity can serve as a practical demarcation line between gas-like and liquid-like regimes.