Solvent-mediated molar conductivity of protic ionic liquids

Abstract

The molar conductivity, Λ_m, of protic ionic liquids (PILs) in molecular solvents is measured at 298.15 K. The decrease in the Λ_m values of PILs is observed with an increase in the concentration of PILs. The limiting molar conductivities, Λ⁰_m, were obtained for each PIL in different molecular solvents using a least squares method. The Λ⁰_m data for PILs were correlated with the structural aspects of PILs and solvent properties. The polar protic solvents show poor ionic association as compared to the polar aprotic solvents, which is discussed on the basis of the hydrogen bond donating (HBD) ability of solvents and PILs. The alkyl chain substitution of anions plays a significant role in the ionic association of the PILs. The diffusion coefficient D⁰ and the transport number t were determined, which were consistent with the Λ⁰_m values of PILs in water. The Λ⁰_m and D⁰ values are dependent on the hydrodynamic radius of anions of these ionic liquids. The extent of ionic association for each PIL was discussed using temperature dependent Λ_m data for aqueous PIL systems in terms of the Walden plot.