Effect of Alkyl Chain Elongation on Thermophysical Properties of 1-Alkyl-3-vinylimidazolium Bromide-Based Ionic Liquids and Salts

A series of 1-alkyl-3-vinylimidazolium-based ionic liquids (ILs) and salts that carry unsaturation in the head group on cation, ([CnC═Cim][Br], n = 2, 4, 6, 8, 10, and 12), were synthesized and characterized in the current study. Differential scanning calorimetry and thermogravimetric analysis were used to determine the thermal behavior and evaluate the phase changes of all the obtained ionic compounds. Further investigation was focused on ILs ([CnC═Cim][Br], n = 4, 6, and 8) and their dependence of temperature for density, electrical conductivity, and viscosity. The data were collected within the temperature range T = 293.15–343.15 K and at atmospheric pressure (p = 0.1 MPa). The transport properties for three ILs were analyzed using the Vogel–Fulcher–Tammann equation. The correlation between viscosity and molar conductivity has been examined using the Walden rule and ionicity, which indicates that the investigated ILs are found in the largest percentage in the form of ion pairs. The obtained experimental data were compared with the available values from the literature for their corresponding saturated counterparts elucidating the impact of the double bond.