Experimental evidence of a state-point dependent scaling exponent of liquid dynamics

TL;DR

This study provides experimental evidence that the scaling exponent of liquid dynamics varies with state points in certain liquids, challenging the notion of a universal exponent and highlighting the importance of state-dependent analysis.

Contribution

It demonstrates the state-point dependence of the scaling exponent in liquid dynamics through experimental data and reanalysis of multiple liquids, including metallic and model systems.

Findings

The scaling exponent varies with state points in silicone oil and 5PPE.

Agreement between average exponents and relaxation time superposition.

Reanalysis confirms state-point dependence across various liquids.

Abstract

A large class of liquids have hidden scale invariance characterized by a scaling exponent. In this letter we present experimental evidence that the scaling exponent of liquid dynamics is state-point dependent for the glass-forming silicone oil tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl ether (5PPE). From dynamic and thermodynamic properties at equilibrium, we use a method to estimate the value of $\gamma$ at any state point of the pressure-temperature plane, both in the supercooled and normal liquid regimes. We find agreement between the average exponents and the value obtained by superposition of relaxation times over a large range of state-points. We confirm the state-point dependence of $\gamma$ by reanalyzing data of 20 metallic liquids and two model liquids.