Intermolecular Force Quantification for Deciphering Lignin Dissolution Behavior in Solvents

Lignin, the most abundant aromatic polymer in nature, holds immense potential for sustainable chemical production. Deciphering lignin dissolution behavior is essential for suitable solvent selection and achieving efficient conversion. However, the high heterogeneity of lignin and the complex interaction between lignin and solvents increase the difficulty in understanding dissolution behavior. To address this issue, in this work, an intermolecular force quantification method was proposed to establish the correlation between microscopic adhesion force and macroscopic solubility using atomic force microscopy (AFM). By engineering a stable lignin-coated AFM probe/substrate system (thickness >100 nm) via electrostatic adsorption, a precise lignin adhesion force quantification system was successfully established. As adhesion forces decreased from 0.106 to 0.026 mN/m, the lignin solubility surged from 0.06 to 168.49 g/L, indicating a strong relevance. Therefore, the lignin solubility can be readily evaluated via adhesion force quantification. Strikingly, a universal critical adhesion force (0.43 mN/m) across diverse lignin types (enzymatic hydrolysis lignin; alkaline lignin) and solvent systems (γ-valerolactone (GVL)/H2O, dioxane/H2O, acetone/H2O) has been identified, beyond which negligible dissolution occurs. This constant serves as a quantitative ″dissolution threshold″, offering a rapid tool to screen optimal solvents. This work bridges intermolecular force quantification with solubility prediction, advancing rational solvent design for lignin valorization.