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

Abstract

Here we present the heat capacity (Cp) of a series of ten imidazolium based ionic liquids (ILs), mono- and dicationic, with chemical formula CnMIMBr (n = 2, 4, 6, 8, 10, 12, 14, and 16) and Cn(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 Cp 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 Cp predicted by theoretical models and molecular modeling calculations showed reasonable agreement with the experimental Cp 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.

Keywords

• Ionic liquid
• Imidazolium
• Heat capacity
• DSC
• Molecular modeling