Professor Robert Leheny, Johns Hopkins University
Microscopic dynamics underlying yielding and stress relaxation of soft glassy materials
Any solid under applied stress possesses an elastic limit above which it fails. Failure of ductile solids is characterized by yielding, which involves irreversible changes to the material’s microstructure. In the case of amorphous solids, such as glasses, pastes, and gels, the intrinsic disorder of the materials makes identifying these changes difficult. Further, when the shear-induced flow of such soft disordered solids ceases, the stress can display a highly protracted decay. The microscopic dynamics driving this stress relaxation remain poorly understood. This talk presents an overview of coherent x-ray scattering studies on soft glassy nanostructured materials to interrogate the microscopic dynamics of yielding and stress relaxation. The systems in the study include nanocolloidal gels, clay suspensions, and soft nanocolloidal glasses subjected to different programs of in-situ shear strain that provide insight into particle rearrangements at the nanometer scale and their connection to the macroscopic rheology. Time permitting, the talk will also describe how such x-ray measurements can probe mechanical rejuvenation and over-aging of glassy suspensions.