Distinct Cation Roles and Shared Anion Mechanism in Hydroxide-Based Cellulose Solvents

Cellulose dissolution remains a fundamental challenge due to its recalcitrant crystalline structure, governed by interchain hydrogen bonds and dispersion interactions. Hydroxide-based systems are industrially relevant but require energy-intensive subzero temperatures. This study employs molecular dynamics simulations to elucidate the molecular mechanisms underlying the dissolution performance of benzyltrimethylammonium hydroxide (BzMe₃NOH) and NaOH. Na⁺ binds to cellulose primarily through electrostatic interactions, whereas the amphiphilic benzyltrimethylammonium cation (BzMe₃N⁺) engages predominantly via vdW interactions, accumulating along the hydrophobic backbone. Both systems exhibit anion-cellulose interactions with hydroxide ions, forming bifurcated hydrogen bonds that facilitate transient deprotonation of hydroxyl groups. A key thermodynamic advantage of BzMe₃N⁺ is that each cation displaces more water molecules away from cellulose's solvation shell than Na⁺ does, reducing the entropic penalty of dissolution. This work establishes that effective dissolution in hydroxide systems requires a synergistic combination of anion-driven hydrogen-bonding disruption and cation-driven dispersion compensation.