Minima of shear viscosity and thermal conductivity coefficients of classical fluids

TL;DR

This paper investigates the minima of shear viscosity and thermal conductivity in classical fluids, revealing their quasi-universal behavior across different systems and their significance as reference points for fluid transport properties.

Contribution

It demonstrates the quasi-universality of viscosity and thermal conductivity minima in reduced units across various model and real fluids, linking microscopic interactions to macroscopic transport behavior.

Findings

Minima are quasi-universal in reduced units for diverse fluids.

Transport property minima serve as useful reference points.

Crossover between transport mechanisms causes these minima.

Abstract

The shear viscosity and thermal conductivity coefficients of various liquids exhibit minima along certain trajectories on the phase diagram. These minima arise due to the crossover between the momentum and energy transport mechanisms in gas-like and liquid-like regimes. We demonstrate that the magnitudes of the minima are quasi-universal in appropriately reduced units, especially for the viscosity coefficients. Results presented in support of this observation concern the transport properties of three simple model systems with different pairwise interaction potentials (hard spheres, Lennard-Jones, and Coulomb) as well as seven important real atomic and molecular liquids (Ne, Ar, Kr, Xe, CH$_4$, CO$_2$, and N$_2$). The minima in viscosity and thermal conductivity represent useful reference points for fluid transport properties.