Density, viscosity and excess properties in the trihexyltetradecylphosphonium chloride ionic liquid/methanol cosolvent system

Abstract

The volumetric and viscosity behaviors of binary mixtures of (trihexyl(tetradecyl)phosphonium chloride ionic liquid+methanol) ([P14,6,6,6+][Cl−]+MeOH) have been described across the entire range of mol fraction [P14,6,6,6+][Cl−] (xIL=0 to 1) and over a temperature range of (290.15 to 313.15)K at p=0.1MPa. All binary mixtures were liquids completely miscible. The experimental data was used to calculate the excess molar properties of these solutions. The variation of density was used to compute excess molar volumes, VE, and partial molar volumes of each component and the excess thermal expansion coefficients, αPE. For each of these excess parameters, the deviations were observed to be negative over the entire range of mole fraction and temperature. Viscosity deviations, Δη, from the ideal mixtures were calculated from the measured viscosities. Additionally, temperature dependent viscosities were observed to follow an Arrhenius activation model and the activation energy, Ea, of viscous flow was computed. Combined viscosity and volumetric data were used to calculate the excess Gibbs free energy, ΔGmE∗, of activation of viscous flow. The results from the excess solution properties behaviors have been discussed in terms of molecular interactions and support the presence of strong interactions in solution. These interactions are typical of IL aggregation. In this IL/cosolvent system the most significant changes occur up to xIL∼0.4.