Density scaling in viscous liquids: From relaxation times to four-point susceptibilities

TL;DR

This study numerically investigates how the dynamic susceptibility in viscous liquids scales with density and temperature, revealing a direct relation between dynamic correlation volume and relaxation time under density scaling conditions.

Contribution

It demonstrates that the four-point dynamic susceptibility's behavior is invariant along density-temperature paths with constant rho^gamma/T, linking dynamic correlation volume directly to relaxation times.

Findings

Dynamic susceptibility invariance along rho^gamma/T scaling paths

Correlation volume proportional to relaxation time tau

Density scaling linked to pressure-energy fluctuation correlations

Abstract

We present numerical calculations of a four-point dynamic susceptibility, chi_4(t), for the Kob-Andersen Lennard-Jones mixture as a function of temperature T and density rho. Over a relevant range of T and rho, the full t-dependence of chi_4(t) and thus the maximum in chi_4(t), which is proportional to the dynamic correlation volume, are invariant for state points for which the scaling variable rho^gamma/T is constant. The value of the material constant gamma is the same as that which superposes the relaxation time, tau, of the system versus rho^gamma/T. Thus, the dynamic correlation volume is directly related to tau for any thermodynamic condition in the regime where density scaling holds. Finally, we examine the conditions under which the density scaling properties are related to the existence of strong correlations between pressure and energy fluctuations.