Physicochemical properties of low viscous lactam based ionic liquids

Abstract

Lactam based ionic liquids were synthesized by an atom economization process between a lactam such as caprolactam or butyrolactam with a Brønsted acid such as formic acid, acetic acid or hexanoic acid. The density, speed of sound and viscosity were measured at atmospheric pressure and as a function of temperature from T = (293.15 to 333.15) K. The experimental density and viscosity values were fitted with linear and Vogel–Tamman–Fulcher (VTF) equations, respectively and found to be fitting well within the experimental error. Thermodynamically important derived properties such as the coefficient of thermal expansion (α) and isentropic compressibility (βs) were calculated from the experimental density and speed of sound values. Lattice potential energy (UPOT) has been calculated to understand the strength of ionic interaction between the ions and the standard entropy (So) has been estimated to assess the disorder within the fluids. The remarkably low values of viscosity of ionic liquids studied are discussed on the basis of activation energy estimated from the Arrhenius equation. Furthermore, the effect of alkyl chain length on the anion, geometry of the cation and temperature has been analysed for the properties studied.