RISM-Assisted Analysis of the Role of Alkali Metal Hydroxides in the Solvation of Cellulose in Alkali/urea Aqueous Solutions

Abstract

The three-dimensional reference interaction site model theory with the Kovalenko-Hirata closure (3D-RISM-KH) combined with the Kirkwood-Buff integral (KBI) was used to clarify the role of alkali metal hydroxides (MOHs) in cellulose solvation in alkali/urea aqueous solutions. The KBI and excess number of MOHs showed that their access and affinity to cellulose were both in the order LiOH > NaOH > KOH. The cavity and interaction volumes for cellulose indicate that the alkali metal ions closer in proximity to cellulose induce thermal fluctuations of cellulose molecules more easily and cause more electrostatic interactions and hydrogen bonding with cellulose. These calculation results support the hypothesis of cellulose charging up, which claims that cellulose-ion interactions cause cellulose solvation. The energy and chemical potential of cellulose solvation confirmed the affinity and interaction of MOHs with cellulose. Solvent reorganization, whose energy primarily determined the solvation energy, was found to be facilitated by the more proximal MOH when in the presence of urea. 3D-RISM-KH combined with KBI produced quantitative information regarding the distribution and attractive interaction of MOHs (especially LiOH) with cellulose, which clarified their role in cellulose solvation in alkali/urea aqueous solutions.