Investigation of temperature and composition dependence of molecular interactions between phosphonium-based ionic liquid + N, N-dimethylformamide: A study of thermophysical properties

Abstract

Understanding the thermophysical properties of ionic liquids (ILs) with organic solvents is crucial for the development of industrial applications. In this study densities (ρ), ultrasonic sound velocities (u) and viscosities (η) for binary mixtures of tri(butyl) methylphosphonium methylsulfate ([P4441][CH3SO4]) with N,N-dimethylformamide (DMF) were measured over the entire composition range at various temperatures (293.15–323.15 K) and at 0.1 MPa pressure. From ρ, u and η data, derived properties such as deviation in viscosities (Δη), excess molar volumes (VE) deviation in isentropic compressibilities (Δκs), mixture molar volume (Vm) volume fraction (θ1) excess expansion volume coefficient (αEp) and adiabatic compressibility (ks) and excess adiabatic compressibility (ksE), Partial molar volumes (V¯1 and V¯2) and excess partial molar volumes (V¯1Eand V¯2E) were calculated. For all the systems studied, negative to positive VE values were obtained while the Δκs and Δη values are negative, over the entire composition range and at all the studied temperatures. Results for these experimental and derived properties have been studied on the basis of intermolecular interactions between the components of the mixtures and in terms of hydrogen bonding, ion-dipole interaction and interstitial packing between ions of IL and molecular solvent. These experimental results and derived properties are beneficial for defining the molecular modelling, developing structure-property correlation and intermolecular interactions that occur between tri(butyl) methylphosphonium methylsulfate with DMF.