Binary deep eutectic solvent mixtures: tunable properties through competitive hydrogen bonding in ChCl-urea/ChCl-ethylene glycol systems

Abstract

Deep eutectic solvents (DESs) based on choline chloride (ChCl) with urea or ethylene glycol as hydrogen bond donors have emerged as versatile, sustainable media with tunable properties. In this work, we present a comprehensive multiscale investigation of binary mixtures spanning the full composition range between ChCl:urea (1:2) and ChCl:ethylene glycol (1:2), aiming to elucidate the structure–property relationships governing their behavior. Thermophysical characterization reveals non-ideal mixing behavior, with distinct trends in the considered properties, reflecting complex molecular interactions. Raman spectroscopy provides molecular-level insights into intermolecular interactions, and structural reorganization across the composition spectrum, with spectral shifts indicating preferential solvation and emergent supramolecular motifs. Molecular dynamics simulations complement the experimental findings, uncovering the evolution of local coordination environments, hydrogen bond networks, and dynamic heterogeneity as a function of mixture composition. The integration of experimental and computational data enables a unified understanding of these mixed DESs, offering valuable design principles for tailoring physicochemical properties in solvent engineering, catalysis, and separation processes.