Phase Behavior of Acetylated Cellulose Nanocrystals and Origins of the Cross-Hatch Birefringent Texture

Cellulose nanocrystals hydrolyzed by hydrochloric acid and esterified by acetic acid produce acetylated cellulose nanocrystals (CNC-AA) with acetyl ester surface functional groups. While much attention has been paid to understanding the phase behavior (liquid crystal) of aqueous dispersions of sulfonated nanocrystals, relatively few studies have focused on CNC-AA dispersions. CNC-AA dispersions exhibit multiple phase regimes and markedly different phase behavior due to their lower surface charge. At concentrations above 5.0 × 10–4%vol, a decrease in the apparent diffusion coefficient indicates the onset of interparticle interactions and a transition from the dilute regime. From 0.003 to 0.31%vol, biphasic behavior is observed, consisting of a birefringent lower phase and disordered or isotropic upper phase. Small-angle neutron scattering was used to measure the growth of fractal structures with increasing concentration and indicates a two-dimensional assembly with short-range order in a plate-like assembl...