The Thermodynamic and Excess Properties of Trialkyl-Substituted Imidazolium-Based Ionic Liquids with Thiocyanate and Its Binary Systems with Acetonitrile

Abstract

Two kinds of new ionic liquids (ILs), 1,2-dimethyl-3-propylimidazolium thiocyanate ([C3mmim][SCN]) and 1-butyl-2,3-dimethylimidazolium thiocyanate ([C4mmim][SCN]), were synthesized and characterized by various methods. Then, the [C3mmim][SCN] and [C4mmim][SCN] were blended with acetonitrile (ACN) to prepare binary IL-based mixture systems over the whole concentration range (molar ratio of IL from 1 to 0). The densities, electrical conductivities, and dynamic viscosities of two pure ILs and two binary systems were determined from 288.15 to 323.15 K. The measured values of the surface tension are used in the calculation of interstice model. The temperature dependence of the transport properties (dynamic viscosity and electrical conductivity) is described by the Vogel–Fulcher–Tamman (VFT) equation and the Arrhenius equation, respectively. The volumetric properties like the thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy of the ILs are estimated through the empiric/semiempirical methods. The excess molar volumes (VE) and dynamic viscosity deviations (Δη) of the mixtures are calculated. For further research, the Redlich–Kister polynomial equation is used to fit the excess molar volume and the deviation in dynamic viscosity data. The negative values of the entire composition range of excess properties clearly indicate the existence of molecular interactions between the studied components.