Active crowds and active elastic solids subject to hydrodynamic, viscoelastic, and elastic interactions in thin enclosing layers

• Applicant: Professor Dr. Andreas Menzel
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541972050

Understanding the emergence of collective motion in crowds of self-propelled objects is fascinating and at the same time of fundamental importance for revealing the properties of active matter in general. Individual entities can align their propagation directions in such crowds due to mutual alignment interactions. However, also the role of a surrounding medium may support the onset of collective migration. The latter effect has mainly been studied for active microswimmers suspended in bulk viscous fluids under low-Reynolds-number conditions. We here extend such investigations on basic properties of active matter into three timely directions. First, we address surrounding media represented by thin layers on a substrate or free-standing films, implying a two-dimensional evaluation. These media laterally enclose the active objects. Due to the presence of the enclosing media, additional interactions between the active objects arise. Second, we focus on the effect of viscoelasticity of the surrounding media. That is, simultaneous elasticity needs to be included in the evaluations besides flow effects. Such situations are frequently encountered in biological settings, but are likewise found for synthetic particles in model experiments designed in this regard. Complete elasticity represents a limiting case. Third, we investigate the dynamics of active solids. Both elastic spring networks as models for elastic solids and cohesive crowds of self-propelled objects are considered to this end. As a result, we reveal the overall and internal dynamics of active crowds and active solids under confinement and in viscoelastic environments. The contribution of each of these aspects is quantified. Integrating these contributions supports the transfer of central fundamental concepts from the research on basic theoretical and artificial model systems to investigations on biological systems. Our topics are chosen in a way to allow for collaboration and joint progress together with leading experimental groups in the field. As expansions of our investigations, we think of associated studies on motility-induced phase separation and derivations of corresponding statistical field theories.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partner: Dr. Olivier Dauchot