Multiscale characterization of hierarchical nanostructured fluid flows

Licentiate thesis, 2025

Natural hierarchical materials such as wood and bone exhibit multifunctional properties due to their precise orientation and alignment across multiple length and time scales. The study of material'building blocks' capable of forming such hierarchies, usually from the point of view of 'self-assembly' is inspired by such natural materials. Among the many examples, one-dimensional (1D) rod-like cellulose nanocrystals (CNCs) and two-dimensional (2D) Graphene oxide (GO) platelets can self-assemble in water into hierarchical structures spanning from atomic, molecular, primary nanoparticles, mesoscale structures thereof to macroscale structures. These mesoscopic domains can take the form of liquid crystalline phases (E.g., nematic, chiral nematic etc. phases), which govern their positional and directional ordering. Such ordering can be utilized to achieve high throughput. However, the inherent structural complexity across scales necessitates simultaneous multiscale characterization to understand and control their behavior during processing.
This PhD project focuses on developing and applying advanced hyphenated rheological techniques, i.e. combining rheology with microscopy and scattering to elucidate how these materials reorganize under deformation and flow. A novel integration of rheology, polarized light imaging (PLI), and small-angle X-ray scattering (SAXS) enabled real-time observation of orientation propagation under simple shear. Furthermore, a Taylor–Couette (TC) geometry, combined with SAXS, revealed the interplay between particle morphology and/or size and vortex structures during transitional flow. To explore the evolution of mesoscopic structures, we are also developing a new technique that couples rheology with nonlinear optics. Overall, this research establishes comprehensive techniques for probing structure-property relationships across length and time scales, and lays the groundwork for hierarchical control in processing applications such as 3D printing.