By Xenocs
Under shear, nanostructures undergo orientation, deformation, or phase reorganization. SAXS/WAXS detects these changes through the evolution of 2D scattering patterns as a function of shear rate. From these measurements, SAXS/WAXS provides: - Orientation of nanodomains, derived from azimuthal intensity distributions - Degree of alignment, quantified through orientation factors or tensor-based analyses - Shear-induced phase transitions, indicated by the appearance, disappearance, or displacement of scattering peaks - Changes in characteristic length scales, such as domain spacing, correlation length, or aggregate dimensions - Coupled nanoscale and atomic-scale responses, when SAXS and WAXS are acquired simultaneously Researchers can perform shear studies continuously (steady shear) or stepwise (oscillatory or transient shear) to directly correlate mechanical conditions with nanostructural evolution. Figure 1. Quantitative analysis of shear-induced structural evolution in cellulose nanocrystals. Orientation factors extracted from radial and tangential SAXS geometries reveal three distinct regimes: an initial isotropic state at low shear rates, a strongly anisotropic alignment regime as shear increases, and a return toward isotropy at high shear due to flow-induced reorganization. The alignment trends mirror rheo-SAXS results, confirming the accuracy of laboratory-based shearSAXS in capturing flow-driven transitions. Shear studies can be performed continuously (during steady shear) or stepwise (in oscillatory or transient shear), enabling direct correlation between mechanical conditions and nanostructural evolution. SAXS/WAXS shear studies are applicable to a broad class of soft and complex materials, including: - Block copolymers, micelles, and polymer solutions - Liquid-crystalline polymers and surfactants - Hydrogels and soft biomaterials - Colloidal dispersions and nanoparticles in solution - Concentrated emulsions or structured fluids - Molten or semi-crystalline polymers under processing-like conditions Measurements can be carried out using a temperature-controlled Couette cell or shear cell adapted to liquids, gels, or soft solids. SAXS and WAXS offer unique advantages for understanding how materials reorganize under mechanical deformation: Direct visualization of flow-induced ordering Including isotropic-to-aligned transitions to complex shear-banding behavior. Quantitative orientation analysis Enabling extraction of alignment factors and orientation distributions. Correlated insight from atomic to nanoscale structures Enabled by simultaneous WAXS and SAXS measurement. Non-destructive probing Suitable for turbid, opaque, viscous, or highly concentrated samples. Real-time monitoring Capturing anisotropy, transitions, or relaxation during shear. Compatibility with realistic processing conditions Supporting studies relevant to coating, printing, fiber spinning, and extrusion. These capabilities make shearSAXS an essential tool for understanding how flow governs structure formation.
