Experimental study and MD simulation of neutral choline–based deep eutectic solvents regulated by ethanol

This study focuses on deep eutectic solvent (DES) systems composed of choline chloride and four alcohol-based hydrogen bond donors (glycerol, 1,3-propylene glycol, 1,2-propylene glycol, and 2,3-butylene glycol), with ethanol added at mole fractions ranging from 0 to 1. Experimental measurements of density and viscosity were conducted, and the results were validated using molecular dynamics (MD) simulations based on the GAFF force field and RESP2 charge model. The simulation results closely matched the experimental data, confirming the accuracy of the modeling approach. Radial distribution function and hydrogen bond analyses revealed that ethanol disrupts hydrogen bonds formed between the choline cation (CHO + ) and the anion (Cl − ), between the anion (Cl − ) and the hydrogen bond donor (HBD), and among HBD molecules themselves. Instead, ethanol forms weaker new bonds with CHO + , Cl − , and HBD. Consequently, at ethanol mass fractions of 49%, 53%, 43%, and 40% in the four systems, viscosity decreased by 96%, 88%, 93%, and 93%, respectively. Despite these changes, the overall DES hydrogen bond network remained largely intact. These findings demonstrate that ethanol effectively tunes the microstructure and viscosity of DESs, enhancing their potential for practical applications.