Visualizing the Shear Flow-Modulated Alignments in Cellulose Nanocrystal Films by the Mueller Matrix

The microstructures of cellulose nanocrystal (CNC) films grown from their aqueous suspensions are tuned by a shear flow during the formation of the films. The modulation of the chiral nematic organization of CNCs is visualized by the complete polarization analysis using Mueller matrix microscopy. Further optical simulation has ensured the comprehensive 3D structural analysis for the complex chiral structures of CNC films. As suggested by the optical investigation, regulating the helical structure under the shear flow involves two transition processes, an early in-plane unwinding, followed by a later helically vertical unwinding. We have also confirmed that sufficient shearing is required to reorient the helically aligned CNCs to form the nematic structure.