Prediction and elucidation of cellulose solubility in ionic liquids under high pressure using all-atom molecular dynamics simulations

Abstract

This study investigated the pressure dependence of cellulose solubility in a 60 wt% ionic-liquid mixture of 1-ethyl-3-methylimidazolium acetate and dimethyl sulfoxide ([EMIm][OAc]/DMSO) using all-atom molecular dynamics simulations conducted over a wide pressure range (P = 0.1–1000 MPa) at temperature T = 500 K. The dissolution free energy obtained via the umbrella sampling method (36 windows, 200 ns each) decreased monotonically as pressure increased, indicating that solubility enhanced at elevated pressures. The underlying molecular mechanism was elucidated by performing 100 ns NPT-MD simulations of a 36-chain cellulose system in 60 wt% [EMIm][OAc]/DMSO at each pressure. Analysis of the radial distribution functions, coordination numbers, interaction energies, chain dispersibility, hydrogen bond populations, and conformational transitions revealed a dual mechanism: (1) pressure-induced compression strengthens solute–solvent interactions and weakens cellulose–cellulose contacts, promoting chain dispersion; and (2) conformational rearrangements of the C6 hydroxyl groups disrupt intramolecular hydrogen bonds and favor new intermolecular hydrogen bonding with [OAc]⁻ anions. This molecular-level insight demonstrated that pressure enhances cellulose solubility through both volumetric compression and active conformational mechanisms, thereby providing guidance for the design of high-pressure cellulose dissolution processes.