Nanoscale Assembly of Cellulose Nanocrystals during Drying and Redispersion

We have followed the structural evolution during evaporation-induced self-assembly of sulfonated cellulose nanocrystal (CNC) in the presence of H⁺ and Li⁺ counterions by small-angle X-ray scattering. Drying of CNC-H dispersions results in ordered films that could not be readily redispersed, while the CNC-Li films were disordered and prone to reswelling and redispersion. The scaling of the separation distance (d) between CNC particles and the particle concentration (c) shows that the CNC-H dispersions display a unidimensional contraction of the nematic structure (d ∝ c^-1) during drying, while the CNC-Li dispersions consolidate isotropically (d ∝ c^-1/3), which is characteristic for hydrogels with no preferential orientation. Temporal evolution of the structure factor and complementary dynamic light-scattering measurements show that CNC-Li is more aggregated than CNC-H during evaporation-induced assembly. Insights on the structural evolution during CNC assembly and redispersion can promote development of novel and optimized processing routes of nanocellulose-based materials.