Thermophysical Study of 1-Butyl-2-methylpyridinium bis(trifluoromethylsulfonyl)imide and 1-Butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide.

Ionic liquids are of great interest for scientists and chemical industries owing to their fascinating properties and their versatile applications. Herein, we focus on the thermophysical properties of two isomeric pyridinium-based ionic liquids: 1-butyl-2-methylpyridinium bis(trifluoromethylsulfonyl)imide and 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide. Experimental investigation of the liquids involved the measurement of their thermodynamic and transport properties, namely, density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, kinematic viscosity, and electrical conductivity. These measurements were performed in the temperature range of 278.15-323.15 K and ambient pressure of 100 kPa. Subsequently, additional properties such as isobaric expansivity, isentropic compressibility, free molar volume, and dynamic viscosity were calculated. Results were discussed considering the structural differences between the isomers, particularly focusing on the influence of the alkyl chain position in the cation on the investigated properties.