Experimental and theoretical heat capacity of mono- and dicationic long alkyl chain imidazolium-based ionic liquids

Abstract

Here we present the heat capacity (C_p) of a series of ten imidazolium based ionic liquids (ILs), mono- and dicationic, with chemical formula C_nMIMBr (n = 2, 4, 6, 8, 10, 12, 14, and 16) and C_n(MIM)₂Br₂, (n = 4 and 8), respectively. The heat capacity values of eight ILs were determined using modulated differential scanning calorimetry (MDSC) in the temperature range of (358.15 to 378.15) K and compared with the results obtained from theoretical models found in the literature and molecular modeling calculations. For this set of ILs the C_p values were found to be in the range of (189.3 to 985.7) J mol⁻¹ K⁻¹. A linear increase in heat capacity with temperature was observed for all ILs. The C_p predicted by theoretical models and molecular modeling calculations showed reasonable agreement with the experimental C_p values for the majority of the studied ILs. The heat capacity increased with the addition of methylene groups in the side and spacer chains for both mono- and dicationic ILs. Consistent with the literature, it is observed that the additional methylene groups have a larger effect on the heat capacity at higher temperature.