Density Scaling and Decoupling in o-Terphenyl, Salol, and Dibutyphthalate

TL;DR

This study demonstrates that o-terphenyl, salol, and dibutylphthalate all follow density scaling in their viscosity and relaxation times across various conditions, with no decoupling observed, correcting previous misconceptions.

Contribution

It provides new high-pressure viscosity and EoS data confirming that these liquids conform to density scaling without exceptions, clarifying prior conflicting results.

Findings

All three liquids follow density scaling across conditions.

No decoupling of viscosity and relaxation times observed.

Previous conflicting results were due to data errors.

Abstract

We present new viscosity and equation of state (EoS) results extending to high pressures for o-terphenyl, salol, and dibutylphthalate. Using these and data from the literature, we show that the three liquids all conform to density scaling; that is, their reduce viscosities and reorientational relaxation times are a function of the ratio of temperature and density with the latter raised to a constant. Moreover, the functional form of the dependence on this ratio is independent of the experimental probe of the dynamics. This means that there is no decoupling of the viscosities and relaxation times over the measured range of conditions. Previous literature at odds with these results were based on erroneous extrapolations of the EoS or problematic diamond anvil viscosity data. Thus, there are no exceptions to the experimental fact that every non-associated liquid complies with density scaling with an invariant scaling exponent.