Speaker
Description
Rheo-small-angle scattering (Rheo-SAS) is a materials characterization methodology that combines the nano and microscale structural insights from SAS with the bulk mechanical property revelations of rheological measurements. Upon application of shear, materials often align along the direction of the flow, showing macroscopic ordering, and the microstructure underpinnings also show rearrangement into anisotropic forms. In SAS, the information about the anisotropic orientation would be lost with the azimuthal averaging performed to obtain 1D profiles. This is why we take the entire 2D profiles, interpreting them using CREASE-2D (computational reverse engineering analysis of scattering experiments), a computational workflow that generates representative structures and correlates the implicit and predefined structural features to scattering profiles. Subsequently a genetic algorithm and similarity metric compare computed 2D profiles to the input experimental profiles to determine the structural features in the experimental system. This is here applied to wormlike micellar systems found in dipeptide hydrogels. We here show how the evolution of viscosity upon application of shear both shapes and is shaped by the underlying nano and micro scale structural evolution. In our work, we see the immediate ordering of nanotubes along the shear direction with a concurrent reduction in diameter of those nanotubes, gradually relaxing into thin but floppier structures.