Physical properties of pyridinium ionic liquids

Abstract

Physical properties like density, viscosity, surface tension and the thermal stability of a series of pyridinium ionic liquids (ILs) with different cationic structures: 1-ethylpyridinium [C2py], 1-butylpyridinium [C4py], 1-butyl-2-methylpyridinium [C4-2-C1py], 1-butyl-3-methylpyridinium [C4-3-C1py], 1-butyl-4-methylpyridinium [C4-4-C1py], 1-hexylpyridinium [C6py] combined with an anion bis(trifluoromethylsulfonyl)imide [NTf2], and 1-butyl-3-methylpyridinium trifluoromethanesulfonate [C4-3-C1py][OTf], 1-butyl-3-methylpyridinium tetrafluoroborate [C4-3-C1py][BF4], and 1-butyl-3-methylpyridinium tris(pentafluoroethyl)trifluorophosphate [C4-3-C1py][FAP] were measured over a wide temperature range. Furthermore the Arrhenius equation and Vogel–Fulcher–Tammann equation have been used to correlate the variation of viscosity of studied ILs with the temperature. Moreover entropy and enthalpy of surface formation per unit surface area of pyridinium ILs have been calculated. The thermal stability of all pyridinium ILs was also investigated at heating rate of 15K·min−1, in the temperatures range 300 to1000K using thermogravimetric analysis instruments (TGA).