The “anomalous” dynamics of decahyroisoquinoline revisited

Abstract

Decahydroisoquinoline (DHIQ) appears to be a unique material-the only non-associated, simple liquid with dynamics deviating from density scaling. To examine whether this anomaly is real, the density, ρ, of DHIQ was measured at temperatures, T, as low as 214 K and pressures up to ∼1.2 GPa. This enabled the equation of state (EoS) to be determined, without extrapolation, over the range of thermodynamic conditions for which the relaxation times had been reported. Using this less ambiguous EoS, we find that within the precision of the available relaxation times, the latter are a function of T/ρ(3.9), contrary to previous reports. Thus, the behavior of DHIQ is unexceptional; similar to every non-associated liquid tested to date, its dynamics comply with density scaling.

On the pressure dependence of the thermodynamical scaling exponent γ

“…In the literature it has lengthily been debated whether the exponent of the thermodynamical scaling, , for nonassociated liquids is constant or state-point dependent. [6,7,8,9,10,11,12,13] It has been showed for many materials that a constant  gives a very good superposition of various dynamic properties over a broad range of density and temperature. However, in a recent investigation we have found unequivocal evidence that dielectric relaxation data for a nonassociated liquid (DC704) cannot be scaled according to eq.…”

Density scaling and decoupling in o-terphenyl, salol, and dibutyphthalate

“…1 for sufficiently large density changes; that is, γ may not remain constant. However, such deviations entail long extrapolations of the equation of state (EoS) [20,21], which opens to question the accuracy of the results. Nevertheless, considering the failure of density scaling at very high ρ in MDS [16], high pressure experimental data are of great interest.…”

On the experimental determination of the repulsive component of the potential from high pressure measurements: What is special about twelve?

“…These findings were anomalous, and subsequent reports showed some inconsistencies in the experimental data of DC704 and DHIQ. 14,15 For the case of DBP, it was found 16 that there were some inconsistencies with the high pressure viscosity data utilized in Ref. [12], however, even rejecting the viscosity data, an optimal scaling was not found to be possible, and deviation from the scaling was evident in the dielectric data at long times [16] In particular, the deviation of DBP from the thermodynamical scaling accord-ing to Ref.. [11] corresponds to an increase of γ with increasing density (and pressure) from 2.6 to 3.9.…”