The mechanism of self-assembly of lignin in deep eutectic solvent based on sulfamic acid and urea through molecular dynamics simulation

Due to the diversity of industrial lignin sources and the complexity of its structure, its application as a high-value material is limited. Lignin nanoparticles (LNPs) have emerged as a hotspot for research due to their advantages of high specific surface area and high dispersion and the solvent transfer method is commonly used for the preparation of LNPs. In this paper, LNPs were prepared by solvent transfer method using DES based on sulfamic acid and urea (S/U DES) as solvent and water as anti-solvent. To explore the internal mechanism of the self-assembly of nanoparticles, a theoretical model of the solvent system and model lignin compound was constructed with the assistance of quantum chemistry and molecular dynamics theories. Through classical molecular dynamics (MD) simulations, the interaction energy, radius of gyration (ROG), solvent accessible surface area (SASS), radial and spatial distribution function (RDFs/SDFs), hydrogen bonding, and the morphology changes were analyzed to reveal the internal mechanism of self-assembly of model lignin compounds in S/U DES. This study is useful in revealing the mechanism of interaction between lignin and DES, as well as providing a benchmark for the green and efficient preparation of lignin nanoparticles.