Imidazolium Based Ionic Liquids: Impact of the Cation Symmetry and Alkyl Chain Length on the Enthalpy of Vaporization

The vaporization thermodynamics of symmetric imidazolium based ionic liquids of the general formula [CnCnIm][Br] with the chains length n = 4, 5, 6, and 8 were investigated using a combination of DSC, TGA, and QCM methods with quantum chemical calculations. Comparison of vaporization enthalpies for the symmetric ([CnCnIm][Br]) and asymmetric imidazolium based ILs ([Cnmim][Br]) revealed a general trend with the lower vaporization enthalpies of the symmetric species indicating a significant decrease of the Coulombic interactions affecting energetics of vaporization.