Impact of sonication on the rheological and colloidal properties of highly concentrated cellulose nanocrystal suspensions

The effect of sonication on a highly concentrated commercial suspension of cellulose nanocrystals (CNCs) and the resulting rheological properties have been investigated. Rheology and structural analysis techniques (atomic force microscopy, small-angle X-ray scattering, transmission electron microscopy and dynamic light scattering) were used to characterize the CNC suspension before and after sonication as a function of concentration. The highly concentrated CNC suspension, which does not contain aggregates, as shown by AFM and TEM imaging, turns from a “gel” form into a “liquid” form after a sonication treatment. The self-organization properties of as-prepared and sonicated suspensions were compared by the determination of their phase diagrams and flow rheology was performed to understand the viscosity behavior as a function of concentration for both systems. Sonication induced a decrease of the inter-particular distance, a strong decrease of the viscosity and remarkable changes in the liquid crystalline behavior, while sonicated and non-sonicated suspensions were stable over time. These effects can be attributed to a decrease in the aspect ratio of the suspended particles, which varies from a high value before sonication due to the presence of elongated bundles to a lower value after sonication that promotes individualization.