Saturated and compressed liquid heat capacity at constant volume for 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide)

One-phase liquid and two-phase liquid + vapour equilibrium, isochoric heat capacities () and densities () were measured for ionic liquid (IL) 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C₆mim][NTf₂]). Measurements were concentrated near the liquid-gas phase transition curve in order to closely observe the changes. The measurements have been made over the temperature range from (330 to 480) K and pressures up to 20 MPa using a high-temperature, high-pressure, nearly constant volume adiabatic calorimeter. The values of temperature at the liquid-gas phase transition curve for each measured isochore (phase transition parameters, ) were obtained by analysis of the quasistatic thermograms (readings of PRT, <i>T</i>− plot) and barograms (readings of the pressure transducer, <i>P</i>− plot). The combined expanded uncertainty of the density, , and isochoric heat capacity, , measurements at the 95% confidence level with a coverage factor of <i>k </i>= 2 is estimated to be 0.06% and 2.0%, respectively.