(342f) Investigating the Shear Induced Microstructure of Cellulose Nanocrystal Dispersions Using Rheo-Small Angle Neutron Scattering (Rheo-SANS)

Cellulose nanocrystals (CNC) produced by sulfuric acid hydrolysis form a cholesteric liquid crystalline phase when dispersed in water. CNC films can exhibit a number of interesting optical properties including iridescence, interference colors, selective reflection, and optical anisotropy. However, in order to get the desired properties, the microstructure of the film must be precisely controlled. Mechanical shear has been proposed as one method to alter the microstructure of CNC in dispersion. The shear induced microstructure can then be preserved in a dried film if the drying time is less than the relaxation time. In this work rheology and small angle neutron scattering (Rheo-SANS) was used to characterize the shear induced microstructure of CNC dispersions in the isotropic, biphasic, and liquid crystalline regimes. Enhanced ordering was seen in the biphasic and liquid crystalline dispersions with increasing shear rate. Additionally, the evolution of the microstructure was monitored during relaxation after shear. These results lead to a better understanding of CNC dispersion microstructure in shear flow and form the basis for preparing optical CNC films with precisely controlled microstructure.