Multiscale Rheo-Optical and Scattering Signatures of Deformation-Induced Anisotropy in Aqueous Cellulose Nanocrystal Suspensions under Large-Amplitude Oscillatory Shear

Abstract

Abstract Aqueous surface-charged cellulose nanocrystal (CNC) suspensions exhibit concentration-dependent viscosity growth, gelation, and deformation-induced anisotropy, but the concentration and strain-amplitude ranges over which these responses emerge are not necessarily the same. Here, low-shear rheology and linear viscoelasticity are combined with rheo-polarized imaging (Rheo-PI) and rheo-small-angle light scattering (Rheo-SALS) to compare mechanical, optical, and scattering signatures in the same CNC system. Analysis of the operational low-rate viscosity and the Winter–Chambon criterion separates an empirical viscosity-crossover concentration, Ccross, from the sol–gel transition concentration, Cg. Under fixed-frequency large-amplitude oscillatory shear (LAOS), nonphase-resolved but directly comparable Rheo-PI and Rheo-SALS readouts show that annularly averaged Rheo-PI retardation becomes detectable at lower concentrations and lower strain amplitudes than those required for the appearance of anisotropic X-shaped SALS patterns. The first optical transition approximately coincides with an apparent contraction of initially circular SALS patterns, whereas clearly directional X-shaped SALS patterns appear only at larger strain amplitudes. The X-shaped lobe geometry then evolves continuously with the strain amplitude, providing a later SALS-based signature of directional mesoscopic anisotropy under the imposed LAOS conditions. Together, these results provide a comparative multiscale map of deformation-induced anisotropy in CNC suspensions and distinguish viscosity crossover, gelation, local optical anisotropy, mechanical yielding, and anisotropic scattering signatures as related but noncoincident responses.

The authors' abstract, as published at the source. Langmuir, 2026 · DOI ↗