Physicochemical properties of 2-alkyl-1-ethylpyridinium based ionic liquids

Abstract

In this work, the effect of the alkyl chain size in 1-ethylpyridinium cation-based ionic liquids are used to explore the nanostructuration effect. Densities and viscosities and their dependence on temperature were measured for the 2-alkyl-1-ethylpyridinium bis(trifluoromethanesulfonyl)imide, [2CN−21C2Py][NTf2] (N = 4, 5, 6, 7, 8, 9, 10, 11, 12) ionic liquid series. Molar volume, thermal expansion coefficients, VFT parameters, as well as, the energy barrier related to the fluid shear at T = 298.15 K, were derived. Highly precise measurements of the heat capacities, at T = 298.15 K, were performed using a drop calorimeter. In agreement with the previously studies based on the alkylimidazolium ionic liquids series, the studied thermophysical and transport properties of the series presents an indication that in the pyridinium based ionic liquids the nanostructuration is intensified after a critical alkyl length, [2C51C2Py][NTf2]. The observed trend shift in the viscosity and heat capacities of the pyridinium ionic liquids is more pronounced in the pyridinium than in the imidazolium ionic liquids series.