Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

An Entropy Scaling Demarcation of Gas- and Liquid-like Fluid Behaviors



Ian H. Bell, Guillaume Galliero, Stephanie Delage-Santacreu, Lorenzo Costigliola


In this work we propose a generic and simple definition of a line separating gas-like and liquid-like fluid behaviors in the supercritical region. We argue that this line is defined by the location of the minimum of the macroscopically scaled viscosity when plotted as a function of the excess entropy, which differs from the popular Widom and Frenkel lines. For hard sphere, Lennard-Jones, and inverse-power-law fluids, such a line is located at a excess entropy approximately equal to -2/3 times Boltzmann's constant and corresponds to points in the thermodynamic space for which the kinetic contribution to viscosity is approximately half of the total viscosity. For flexible Lennard-Jones chains, the transitional excess entropy is a linear function of the chain length. This definition opens a straightforward route to classify the dynamic behavior of supercritical fluids from a single thermodynamic quantity obtainable from high-accuracy thermodynamic models. This methodology also applies to fluids without attraction, unlike the Widom lines.
The Journal of Chemical Physics


Bell, I. , Galliero, G. , Delage-Santacreu, S. and Costigliola, L. (2020), An Entropy Scaling Demarcation of Gas- and Liquid-like Fluid Behaviors, The Journal of Chemical Physics, [online], (Accessed April 13, 2024)
Created March 31, 2020, Updated July 8, 2020