Quasi-universal behaviour of shear relaxation times in simple fluids

TL;DR

This study reveals that shear relaxation times in various simple fluids show a quasi-universal pattern when expressed in reduced units, decreasing then increasing with density, with similar values at minima and phase transition points.

Contribution

It demonstrates the quasi-universal behavior of shear relaxation times across different simple fluids in reduced units, spanning a wide range of densities.

Findings

Shear relaxation times decrease then increase with density.

Reduced relaxation times are similar at minima and phase transition points.

Universal behavior observed across Lennard-Jones, Yukawa, soft-sphere, and hard-sphere fluids.

Abstract

We calculate the shear relaxation times in four important simple monatomic model fluids: Lennard-Jones, Yukawa, soft-sphere and hard-sphere fluids. It is observed that in properly reduced units, the shear relaxation times exhibit quasi-universal behaviour when the density increases from the gas-like low values to the high-density regime near crystallization. They first decrease with density at low densities, reach minima at moderate densities, and then increase toward the freezing point. The reduced relaxation times at the minima and at the fluid-solid phase transition are all comparable for the various systems investigated, despite more than ten orders of magnitude difference in real systems. Important implications of these results are discussed.