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 (V^E) 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 V^E behavior and confirming mixture stability. Isentropic compressibility deviation (Δκ_S) shows a negative deviation with a minimum at x₁ ≈ 0.15. Excess properties (V^E, Δκ_S and Δη) are correlated by the Redlich–Kister (R–K) polynomial equation. The molar volume (V), lattice energy (U_pot), molar entropy (S⁰), and intermolecular free length (L_f) 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 V^E of a pseudo-binary mixture composed of a DES and water with improved accuracy using the fitted approach.