Yielding of model particle-laden interfaces in shear and compression

Particle-laden interfaces have been extensively used due to their excellent capabilities of imparting stability in multiphase materials in what is called Pickering-Ramsden stability. While particles are usually added in amounts that create maximally packed or multilayer coverages on a bubble or droplet interface, it has been reported that even sub-monolayer coverages can impart a finite interfacial yield stress—already strong enough to arrest bubble dissolution. In the present work, we use a model elastoviscoplastic interface and custom-built interfacial rheometry set-ups to interrogate the yielding behavior in both shear and compressional/dilatational deformation modes while simultaneously looking at the 2D microstructure. Depending on surface coverage, either flocculated networks or densely packed particle-laden interfaces are obtained. We specifically investigate the transition from linear to nonlinear behavior in different rheometric experiments and relate the transitions, from elastic to plastic to viscous deformations, to microstructural observations. With full microstructural resolution in two-dimensional systems being easily accessible, the results inform both the deliberate tuning of interfacial mechanics and provide insights into the fundamental mechanisms governing yield in bulk materials.