(191y) Cellulose Nanocrystals Liquid Crystalline Suspensions: Rheology and Phase Behavior

Cellulose nanocrystals (CNC) have potential to become a non-toxic, renewable, and cost effective nanofiller for biocompatible polymer nanocomposites with a high strength to weight ratio. The elongated nanoparticles have elliptical cross sections and appreciable aspect ratios. CNC with an average length of 130nm, average width of 20nm, and average height of 7nm can be readily isolated from cotton or wood pulp fiber by acid hydrolysis. Aqueous suspensions of CNC behave as an entirely isotropic material at low concentrations; as the concentration is increased the particles don't precipitate nor coagulate, instead they self assemble into a chiral nematic liquid crystalline phase. A two phase region exists between volume fractions of approximately 0.03, and 0.10. When the CNC concentration is further increased, the sample is expected to go through another phase change and form a gel structure. The effect of temperature on the phase behavior and structure of the liquid crystalline suspensions was investigated macroscopically and microscopically using crossed polarizers. The rheological properties were studied as a function of the CNC concentration; transient and steady shear experiments were used to characterize the material. Understanding the flow behavior as well as the structural properties of these suspensions is fundamental for processing of CNC into nanocomposites and other consumer products.