Synergistic interactions and activated anion states: Further insights into the microstructural origin of enhanced cellulose dissolution in [Bmim][OAc]/DMSO solvents

Binary mixtures of ionic liquids (ILs) with dimethylsulfoxide (DMSO) are effective solvents for cellulose, yet the mechanistic role of DMSO remains incompletely understood. This study combines physicochemical characterization, ¹H NMR spectroscopy, COSMO-RS predictions, molecular dynamic (MD) simulations, and cellulose solubility measurements to derive properties—including excess thermodynamic properties, hydrogen bond quantities and structures, pair numbers, hydrogen-bond counts, shortest equilibrium distances, and IL/DMSO–cellulose interactions, to elucidate the microstructural evolution and energy landscapes within mixtures of x 1-butyl-3-methylimidazole acetate ([Bmim][OAc]) + (1 – x ) DMSO, along with experimental cellulose solubility data, to elucidate the enhanced cellulose dissolution mechanism. We reveal that DMSO interactions stabilize IL cations (lowering their energy state) while simultaneously activating IL anions and DMSO molecules (elevating their energy states) through weakened hydrogen bonding. This synergistic effect maximizes at x ≈ 0.3–0.4, forming a unique hydrogen-bonded network characterized by highly activated anions and DMSO, along with stable, hydrogen-bonded-active cations. Consequently, the cellulose-solvent interaction reaches its strongest level, yielding peak cellulose solubility. These findings first provide a link between solvent microstructure, energy landscapes, and solubility, and establish a novel design principle for the regions with the highest cellulose solubility via the properties of ILs/cosolvents mixtures.