Effect of temperature on thermal (density), caloric (heat capacity), acoustic (speed of sound) and transport (viscosity) properties of 1-octyl-3-methylimidazolium hexafluorophosphate at atmospheric pressure

Highlights: • Transport and thermodynamic properties of 1-octyl-3-methylimidazolium hexafluorophosphate. • Density, heat capacity, speed of sound, and viscosity of 1-octyl-3-methylimidazolium hexafluorophosphate. • Vogel-Tamman-Fulcher (VTF) model of the viscosity correlation. • Glass temperature of 1-octyl-3-methylimidazolium hexafluorophosphate. Density$\rho \left(T\right)$, heat capacity$C_P\left(T\right)$, speed of sound$c\left(T\right)$, and viscosity,$\eta \left(T\right)$, were measured for the ionic liquid (IL) 1-octyl-3-methylimidazolium hexafluorophosphate [OMIM][PF₆] at atmospheric pressure as a function of temperature from (278.15 to 413.15) K for the density ($\rho$), from (253.15 to 413.15) K for the heat capacity ($C_P$), from (278.15 to 343.15) K for the speed of sound (c), and from (269.96 to 413.82) K for the viscosity ($\eta$), using various type of commercial instruments. The combined expanded uncertainty of the viscosity, heat capacity, speed of sound, density, and temperature measurements at the 68% confidence level with a coverage factor of k = 2 is estimated to be 0.5% (for SVM 3000 Stabinger viscometer) and 1.5% (for Rheometer MCR 302), 1.5%, ±0.5 m·s⁻¹, 0.23% (including the purity and calibration effects), and 15 mK, respectively. These new experimental data were used to develop wide range correlations for the viscosity based on theoretically confirmed Arrhenius-Andrade and Vogel-Tamman-Fulcher (VTF) models. The value of the glass temperature ($T_g$) for the IL was estimated using the VTF parameters derived from the present viscosity measurements. Measured values of density, heat capacity, and speed of sound were used to calculate other important thermodynamic properties, ${\kappa }_S$,${\kappa }_T$, ${\alpha }_P$, ${\gamma }_V$, $\Delta H$, $C_{\text{V}}$, ${\left(\frac{\partial H}{\partial P}\right)}_T$, and ${\left(\frac{\partial U}{\partial V}\right)}_T$.