Exploring the Physicochemical Properties and PC-SAFT Modeling of a Mixture of Deep Eutectic Solvent (Choline Chloride and Butyric Acid) + Water

This study reports measurement of density (ρ), speed of sound (u), and dynamic viscosity (η) of a choline chloride and butyric acid deep eutectic solvent (ChCl/BA DES) and investigates its physicochemical properties and its aqueous mixtures for the entire range of composition at T = 303.15–343.15 K. The density data are fitted by the second-degree polynomial equation in T, and the fourth-degree polynomial equation in the mole fraction of ChCl/BA DES (x1) is fitted well for both ρ and η. Excess molar volume (VE) shows a positive deviation from ideality with the minimum centered at x1 ≈ 0.5. Viscosity deviation (Δη) exhibits a minimum at x1 ≈ 0.5, aligning with VE behavior and confirming mixture stability. Isentropic compressibility deviation (ΔκS) shows a negative deviation with a minimum at x1 ≈ 0.15. Excess properties (VE, ΔκS and Δη) are correlated by the Redlich–Kister (R–K) polynomial equation. The molar volume (V), lattice energy (Upot), molar entropy (S0), and intermolecular free length (Lf) are evaluated to understand the derived thermodynamic properties. Temperature dependence of η is compared using Vogel–Fulcher–Tammann (VFT) and Arrhenius equations. The PC-SAFT equation of state quantitatively predicts ρ and VE of a pseudo-binary mixture composed of a DES and water with improved accuracy using the fitted approach.