(352g) Yielding and Microstructure in a 2D Jammed Material Under Shear Deformation

Arratia, P. E. - Presenter, University of Pennsylvania

In this talk, we present an experimental investigation on the rheology and microstructure of two-dimensional colloidal suspensions undergoing oscillatory shear. In the experiments, colloidal particles are adsorbed at an oil-water interface and form a dense disordered monolayer. Rheological measurements are performed in a custom-built interfacial stress rheometer, using a magnetic needle within the material. This configuration allows for the simultaneous characterization of both fluid microstructure (tracking ~105 particles) and bulk rheology. Results show that below a certain strain amplitude, the microstructure becomes reversible after a transient. Above this strain amplitude, the microstructure continues to evolve through many irreversible events. We argue that this boundary between a reversible and irreversible steady state is a yielding transition, and that our experiments measure a meaningful yield stress.