Phase transitions of cellulose nanocrystal suspensions from nonlinear oscillatory shear

Cellulose nanocrystals (CNCs) self-assemble in water suspensions into liquid crystalline assemblies. Here, we elucidate the microstructural changes associated with nonlinear deformations in (2-9 wt%) CNC suspensions through nonlinear rheological analysis, that was performed in parallel with coupled rheology-polarized light imaging. We show that nonlinear material parameters from Fourier-transform rheology and stress decomposition are sensitive to all CNC phases investigated, i.e. isotropic, biphasic and liquid crystalline. This is in contrast to steady shear and linear viscoelastic dynamic moduli where the three-region behavior and weak strain overshoot cannot distinguish between biphasic and liquid crystalline phases. Thus, the inter-cycle and intra-cycle nonlinear parameters investigated are a more sensitive approach to relate rheological measurements to CNC phase behavior.