Defect-mediated permeation of deep eutectic solvents in cellulose crystals: A combined experimental and molecular...

Understanding the dissolution mechanism of cellulose in environmentally friendly solvent systems is critical for advancing biomass valorization and green polymer processing. Choline chloride-based deep eutectic solvents (DESs) have emerged as promising alternatives due to their low toxicity, biodegradability, and tunable hydrogen-bonding environments. In this study, molecular dynamics simulations combined with experimental validation were employed to investigate the disassembly of microcrystalline cellulose in choline chloride-based DESs containing both π-conjugated and non-π-conjugated hydrogen bond donors. Notably, systems incorporating π-conjugated hydrogen bond donors, such as imidazole, pyrazole, and 1H-pyrazolo[3,4-c]pyridine, exhibited dual interaction modes, hydrogen bonding and π-π stacking, that synergistically promoted cellulose disruption. These π-conjugated systems demonstrated superior solvation performance, achieving diffusion coefficients of 0.2 to 9.4× 10^-6 cm²/s for cellulose chains and solvation free energies of -69.3 to -75.5 kJ/mol per glucose unit, significantly more favorable than those of non-π-conjugated analogues (-44.7 to -69.6 kJ/mol). In comparison to cellulose treated with non-π-conjugated DES, the solvent-accessible surface area increased by 4.3- to 4.6-fold. Scanning electron microscopy confirmed these findings, revealing pronounced fibril disintegration in samples treated with choline chloride-imidazole. These quantitative insights establish clear design rules for the development of next-generation π-conjugated solvent systems tailored for efficient and sustainable cellulose dissolution.