Journal of Chemical and Engineering Data, Vol.66, No.1, 480-493, 2021
Density, Viscosity, and Electrical Conductivity of 1-Alkyl-3-methylimidazolium Dicyanamide Ionic Liquids
A series of 1-alkyl-3-methylimidazolium dicyanamide ionic liquids ([C(n)mim][N(CN)(2)], n = 2, 3, 4, 5, and 6) were synthesized and characterized in this work. The density, viscosity, and electrical conductivity of these ionic liquids were measured from 293.15 to 353.15 K at 101.3 kPa using a high-precision vibrating tube density meter, an automated falling ball viscometer, and a conductivity meter, respectively. On this basis, the corresponding molar volume and molar conductivity were also obtained. All experimental values were well-fitted by the empirical equations. Remarkably, these ionic liquids exhibit much lower density, lower viscosity, and higher electrical conductivity than many other conventional ionic liquids. According to the theoretical calculations, the weaker cation-anion interaction and V-shaped and nonspherical structure of the dicyanamide anion are considered as major reasons for these properties. Meanwhile, the extension of the alkyl side chain length can result in lower density, higher molar volume, higher viscosity, and lower conductivity. This phenomenon is probably ascribed to the decreasing molecular symmetry, enhanced hydrogen bonding, and increasing steric hindrance of ionic liquids. The relationship between viscosity and molar conductivity has been also investigated using the Walden rule, which confirms the high ionicity of [C(n)mim][N(CN)(2)]. The enhanced dissociation of ions may favor the ionic fluidity and conductivity. It is hoped that these experimental results and theoretical findings may be useful for the future development of dicyanamide-based ionic liquids.