Molecular dynamics studies on the aggregating behaviors of cellulose molecules in NaOH/urea aqueous solution

Abstract

Aggregating behaviors of cellulose molecules in NaOH/urea aqueous solution were investigated using a molecular dynamics (MD) simulation method. All the components, including cellulose, NaOH, urea and H2O were combined into the simulation. By monitoring the transformation of cellulose aggregates, we quantitatively revealed the solvent aggregating behaviors around cellulose molecules in the whole simulation process. And the aggregation evolution of solvent components around cellulose molecules, distributions of the solvent components in cellulose ICs, and the impacts of urea and NaOH in the dissolving process were discussed. In the simulation, the aggregated structure of cellulose molecules was dramatically changed and went through a dispersion process, equilibrium process and reaggregation process. The dramatic transformation of the cellulose aggregated structure indicates that the solvent components prefer to penetrate into the cellulose molecular sheets from the direction perpendicular to the molecular sheet. In the dispersion process, sodium ions around O6 and hydroxide ions around O3 and O2 play crucial roles in the dissolution of cellulose. In the reaggregation process, the sodium ions near O6 and the urea around acetalic oxygen atoms impact the stability of cellulose inclusion complexes, and obvious decrements in these solvent components were observed.