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.
, Galliero, G.
, Delage-Santacreu, S.
and Costigliola, L.
An Entropy Scaling Demarcation of Gas- and Liquid-like Fluid Behaviors, The Journal of Chemical Physics, [online], https://doi.org/10.1063/1.5143854
(Accessed May 31, 2023)