Probing the link between residual entropy and viscosity of molecular fluids and model potentials

TL;DR

This study confirms a scaled relationship between residual entropy and viscosity across various molecular fluids and model potentials, refining Rosenfeld's universal correlation with specific density scaling.

Contribution

It demonstrates that residual entropy can effectively predict viscosity for diverse fluids when combined with proper density scaling, challenging the universality of Rosenfeld's original correlation.

Findings

Residual entropy correlates with viscosity across multiple fluids and models.

Proper density scaling improves the predictive power of the residual entropy-viscosity relationship.

The length scale derived is proportional to the cube root of liquid volume.

Abstract

This work investigates the link between residual entropy and viscosity based on wide-ranging, highly accurate experimental and simulation data. This link was originally postulated by Rosenfeld in 1977, and it is shown that this scaling results in an approximately monovariate relationship between residual entropy and reduced viscosity for a wide range of molecular fluids (argon, methane, CO2, SF6, refrigerant R-134a (1,1,1,2-tetrafluoroethane), refrigerant R-125 (pentafluoroethane), methanol, and water), and a range of model potentials (hard sphere, inverse power, Lennard-Jones, and Weeks-Chandler-Andersen). While the proposed "universal" correlation of Rosenfeld is shown to be far from universal, when used with the appropriate density scaling for molecular fluids, the viscosity of non-associating molecular fluids can be mapped onto the model potentials. This mapping results in a length scale that is proportional to the cube root of experimentally measureable liquid volume values.