| Objectives: The programme aims at unravelling the yielding/jamming (flow-no flow) transitions exhibited by yield stress fluids from a microscopic perspective. The scientific programme is inspired by recent findings of a critical jamming transition which separates rigid and flowing states of disordered materials. The three closely interconnected scientific questions that will be addressed concern (i) the microscopic origin of the jamming of yield stress fluids, (ii) the relation between jamming and the formation of shear bands, and (iii) the cause of shear thickening. Background, relevance and implementation: Because of their enormous range of applications, yield stress fluids, such as drilling fluids, toothpaste, shaving foam, coatings and mayonnaise, have been studied intensively. However, the classical rheological description of these materials, which assumes a constant yield stress, does not capture that yield stresses often depend on the materials history and vary in space and time, does not always correctly predict when yield stress fluids form shear-bands and does not provide an understanding of the behavior of these materials. The missing key ingredient is the coupling between the local flow and the local rheological features, mediated by the microscopic organization of these materials. In this programme a clear framework will be developed by incorporating novel microscopic descriptions that have emerged in the study of jamming. The proposed programme thus weaves the two strands of jamming and rheology together, allowing for the first time to provide a microscopic understanding of the flow of yield stress fluids. In ten sub projects a variety of materials, ranging from foam and macroscopic suspensions to colloidal and clay suspensions will be studied: the focus is on generic mechanisms. In addition, the programme will serve as a nucleus for collaborations with industry. At present, activities in these fields in the Netherlands are growing but scattered across institutes and communities. By bundling these parallel efforts, which individually already have a major impact, we will create a strong and focused programme at the forefront of this field. |
