• Annegret Glitzky, Matthias Liero
• Jürgen Fuhrmann, Manuel Landstorfer
• CRC 1114 Scaling Cascades in Complex Systems with projects C09 and B01
• Luca Heltai (SISSA), Andrea Bertozzi (UCLA), Alexander Mielke (WIAS), Andreas Münch (Oxford), Edriss S. Titi (Cambridge, Texas A&M)

We study continuum formulations for flows of elastic particles immersed in a liquid and their gelation by variational modeling, mathematical analysis, and structure-preserving discretizations. The resulting models will be calibrated using experimental data.

Flows of soft elastic particles suspended in viscous fluids play a fundamental role in biological and geological systems. In microgel suspensions, they offer promising future prospects for engineering and pharmaceutical industries. The viscoelastic properties of these systems vary depending on the particle density: At low densities (dilute regime) mixtures have an effective viscosity and elastic properties are negligible, while for moderate densities (dense regime) particles interact and deform so that the effective flow becomes viscoelastic; such a viscous or viscoelastic suspension is called sol. As the suspension exceeds the dense regime, solid particles become so densely packed that elastic links are formed between them; such a mixture is called gel. Although this sol-gel transition is not yet well-understood, its vital impact on soft matter, biological or medical applications is evident: Examples are plaque formation and drying blood, where platelets enter a condensed aggregate phase, or suspensions of proteins in electrolyte solutions that are prone to form gels by clustering. For these systems the elasticity enters the models via the elastic properties of the particles themselves and via the rheology of the assembled gel. From a mathematical point of view, these models have an intriguing interplay of Lagrangian and Eulerian descriptions, where the availability of corresponding transformation maps is a central open question. In the proposed project we will develop a unified continuum model based on phase indicators for the fluid and the solid phase that encompasses the behavior of both regimes sol and gel and captures the phase transition from one to the other.

For both regimes sol and gel it is the goal of the project i) to deduce a unifying continuum model in terms of a gradient, GENERIC or port-Hamiltonian structure, ii) to carry out mathematical analysis based on this structure and to develop structure-preserving numerical methods. This is the basis iii) to validate the model for the different regimes and to identify physical parameters through experimental data generated by the project. The GFZs experimental tectonics laboratory is equipped with particle image velocimetry (PIV) systems and rheometric setups, from which we will investigate material properties and measure dynamic observables directly comparable to simulations.