Investigation of the physicochemical and thermodynamic characteristics of imidazole ionic liquids with water and ethanol mixtures

The utilization of ionic liquids (ILs) as solvents in the preparation of regenerated cellulose fibers (RCFs) has garnered considerable research attention. The physicochemical properties of the ILs mixtures with coagulants significantly impact the morphology and characteristics of RCFs. This study determines the density and viscosity of 1-ethyl-3- methylimidazolium diethylphosphate ([Emim][DEP]), 1-ethyl-3-methylimidazolium dimethylphosphate ([Emim][DMP]), and 1‑butyl‑3-methylimidazolium dimethylphosphate ([Bmim][DMP]) in mixtures with water and ethanol. The thermodynamic data such as excess molar volumes, viscosity deviation, and excess Gibbs energy of activation for viscous flow, were also calculated and analyzed. The density and viscosity of [Bmim][DMP] is 1.1579 g·cm⁻³ and 367.97 mPa·s at 303 K, and the order of the interaction between different ILs and coagulants was obtained. In the meantime, the water activity of the ILs-water mixtures was also tested, and the constant pressure boiling point of ILs with water and ethanol mixtures was measured. Furthermore, the polar action parameters of ILs were determined by Reichardt's dye. The experimental results obtained have mutually confirmed each other. The investigation of the interaction between ILs and coagulants furnishes foundational data and theoretical support for the controlled formation of RCFs prepared using ILs as solvents.