Tailoring Quaternary Ammonium Deep Eutectic Solvents for Enhanced CO ₂ Gas–Liquid Equilibrium: Synergistic Interactions Revealed by Experiment and Multiscale Simulation

Developing efficient solvents is crucial for carbon capture. This study presents a molecular design of quaternary ammonium-based deep eutectic solvents (DESs) with varied compositions for CO2 capture. Their formation via hydrogen bonding was confirmed by FT-IR and 1H NMR. Physicochemical characterization showed viscosity significantly decreased with temperature. CO2 absorption was primarily pressure-driven (following Henry’s law) and modulated by temperature and solvent composition. An optimal DES (methyltrioctylammonium chloride/lauric acid = 1:2) showed superior capacity due to its hydrogen-bonding network and large free volume. Integration of Hansen Solubility Parameters with XGBoost machine learning identified pressure, temperature, and hydrogen-bonding capacity as key factors. Multiscale simulations verified that van der Waals forces and weak hydrogen bonds drive absorption, with the optimal DES forming a stable microstructure. This work demonstrates how combining synthesis, modeling, and simulation elucidates structure–property relationships, aiding the development of efficient carbon capture solvents.