Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids

TL;DR

This study shows that various linear-response functions in two glass-forming liquids share identical temperature-dependent time scales, supporting the idea that van der Waals liquids behave as strongly correlating, single-parameter liquids.

Contribution

It provides experimental evidence that multiple response functions in van der Waals glass-formers have synchronized temperature dependence, highlighting their single-parameter nature.

Findings

Loss-peak frequencies of response functions are temperature-dependent in unison.

Time scales are ordered from shear modulus to specific heat.

Supports the conjecture of van der Waals liquids being strongly correlating.

Abstract

The frequency-dependent dielectric constant, shear and adiabatic bulk moduli, longitudinal thermal expansion coefficient, and longitudinal specific heat have been measured for two van der Waals glass-forming liquids, tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within the experimental uncertainties the loss-peak frequencies of the measured response functions have identical temperature dependence over a range of temperatures, for which the Maxwell relaxation time varies more than nine orders of magnitude. The time scales are ordered from fastest to slowest as follows: Shear modulus, adiabatic bulk modulus, dielectric constant, longitudinal thermal expansion coefficient, longitudinal specific heat. The ordering is discussed in light of the recent conjecture that van der Waals liquids are strongly correlating, i.e., approximate single-parameter liquids.