Thermodynamic analysis of cellulose complex in NaOH–urea solution using reference interaction site model

Thermodynamic analysis of the empirical data for the solvation of cellulose in aqueous NaOH/urea solution was performed in this study; this was achieved by employing the three-dimensional Reference Interaction Site Model theory coupled with the Kovalenko–Hirata closure approximation. The preferential distributions of Na⁺, OH⁻, urea, and water that were in a close proximity to the cellulose molecule, enabled the calculation of the solvation energy and the contribution of each solvent species to the solvation energy. By dividing the solvation energy into the solvent potential energy under the consideration of the solvent–solute interaction and the solvent reorganization energy, cellulose solvation in the NaOH/urea solution was observed to be primarily due to reorganization of the water molecules around the cellulose molecule. The solvated structure was suggested to be composed of cellulose as an inclusion in helical clusters of Na⁺, OH⁻, urea, and water, wherein the clusters comprised a repeated arrangement of OH⁻ hydrate, water molecules, urea hydrate, and water molecules. Cellulose is suspected to play the role of a water structure maker in the presence of NaOH and urea, and as a water structure breaker in the absence of NaOH and/or urea.