Breakdown and buildup mechanisms of cellulose nanocrystal suspensions under shear and upon relaxation probed by SAXS and SALS

25 February 2021
In this study supervised by Frédéric Pignon (LRP, Grenoble), the complementary use of small-angle scattering of light (structure at the microscopic scale) and X-rays (structure at the nano scale) allowed us to revisit the mechanism of orientation under flow of suspensions of cellulose nanocrystals in the liquid-crystal phase. Click on the title for more information.

Abstract:

“The breakdown and buildup mechanisms in concentrated cellulose nanocrystal (CNC) suspensions under shear and during relaxation upon cessation of shear were accessed by small-angle X-ray and light scattering combined with rheometry. The dynamic structural changes over nanometer to micrometer lengthscales were related to the well-known three-regime rheological behavior. In the shear-thinning regime I, the large liquid crystalline domains were progressively fragmented into micrometer-sized tactoids, with their cholesteric axis aligned perpendicular to the flow direction. The viscosity plateau of regime II was associated to a further disruption into submicrometer-sized elongated tactoids oriented along the velocity direction. At high shear rate, regime III corresponded to the parallel flow of individual CNCs along the velocity direction. Upon cessation of flow, the relaxation process occurred through a three-step buildup mechanisms: i) a fast reassembling of the individual CNCs into a nematic-like organization established up to micrometer lengthscales, ii) a slower formation of oriented large cholesteric domains, and iii) their isotropic redistribution.”

The article is avalaible over here.