Predicting the Density-Scaling Exponent of a Glass-Forming Liquid from Complex Dielectric Permittivity Measurements

One of the challenging problems related to the liquid-glass transition phenomenon is establishing a link between the character of intermolecular interactions and the behavior of molecular dynamics. Introducing the density scaling concept, according to which dynamic quantities, e.g., viscosity or structural relaxation time (τα) measured at different thermodynamic conditions are expressed as a single universal curve if plotted against ργ/T, led to significant progress in solving this problem since the scaling exponent γ defines the steepness of the repulsive part of the intermolecular potential. Herein, we found that relaxation dynamics of van der Waals and H-bonding glass formers, for which the Kirkwood factor (gK) is an isomorph-invariant quantity, satisfy an alternative scaling, logτα vs T(ΔϵsT)-γ. As a result, the exponent γ is determined from the temperature and pressure evolutions of τα and dielectric relaxation strength Δϵ - both obtained in a single dielectric experiment, which makes the γ coefficient to be accessed in the future for an extensive database of glass-forming liquids.