Investigating the interaction potential of [C(n)mim][PF(6)]ionic liquids by using the experimental internal pressure

In this work to explore the behaviour of the internal interactions, the internal pressure of six ionic liquids was calculated from the experimental pVT data. The physical base of the internal pressure is a force tending to close together the molecules that is intermolecular interaction. Therefore, this thermodynamic quantity is a fine measure to investigate the effect of the alkyl group size on the ionic liquids internal interactions. The consisted ionic liquids have a 1-alkyl-3-methylimidazolium cation, where the alkyl group was C(2)H(5), C(4)H(9), C(6)H(13), and C(8)H(17) and PF(6) anion. As it was expected for the alkyl group substituent between 2 – 6 carbons the variation of the internal pressure is similar. For 1-ethyl-3-methylimidazolium cation the maximum value of the internal pressure was obtained and as the chain length increases, the interaction energy does lower due to the delocalization of Columbic packing. However, for a carbon chain length larger than six and beyond, by increasing the carbon chain length the potential varies gradually due to increasing van der Waals forces between R-chains. Finally to estimate the appropriate potential model for the investigated polar fluids, three different reported potential models have been applied to the experimental internal pressure.

Keywords:

Internal pressure , Ionic liquid