Thermodynamic Properties and Internal InteractionBehavior of Carboxyl-Based Deep Eutectic Solvents with 1,4-ButylactoneBinary Mixtures by a Combined Experimental and Calculation Method

In this study, choline chloride ([ChCl]) and three dicarboxylic acids (ethanedioic acid dihydrate ([OA]), malonic acid ([MA]), and glutaric acid ([GA])) were used as raw materials to synthesize three carboxyl-based DESs ([ChCl:OA], [ChCl:MA], and [ChCl:GA]). The excess molar volume (<i>V</i>^E), the molar surface Gibbs energy (<i>g</i>_s), and the excess molar surface Gibbs energy (<i>g</i>_s^E) of DESs + 1, 4-butylactone ([GBL]) binary mixtures were calculated. Owing to the existence of van der Waals forces and hydrogen bonds in the binary mixture, the surface tension of the binary mixture declines as the temperature rises. Based on density functional theory, the interaction energies of all mixed systems can be sorted in the following order: |DESs + 2GBL| > |2DESs + GBL| > |DESs + GBL| > |DESs|. Based on radial distribution functions, the Cl atom in [ChCl], the H₂ atom in [OA], the H₃ atom in [MA], and the H₄ atom in [GA] were investigated as reference sites to demonstrate that the interaction strength between the hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) was consistent across the three systems. These theoretical studies offer significant reference value for the application of various types of mixed systems.