Isobaric Heat Capacities of the Ionic Liquids [Cnmim][Tf2N] (n=6, 8) from (323 to 573) K at 10 MPa

Isobaric volumetric heat capacities (sigma(p)) of the ionic liquids 1-hexyl (or octyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(6)mim][Tf2N] and [C(8)mim][Tf2N], have been measured in the temperature range of 323 <= T/K <= 573 with a Tian-Calvet type differential calorimeter at a pressure of 10 MPa. Isobaric massic (c(p)) and molar (C-p) heat capacities were calculated from the sigma(p) values using densities estimated from literature data. The present C-p values increase approximately linearly with temperature over the investigated range. Where comparison is possible, the present results are in excellent agreement with literature data obtained by adiabatic calorimetry but disagree markedly (by up to 7 %) with those measured by differential scanning calorimetry. Both compounds show evidence of decomposition at T greater than or similar to 535 K, which is in approximate agreement with recent slow scan thermogravimetric measurements but is about 85 K lower than suggested by previous fast scan data.