Project C7: Dense active suspensions in the chaotic regime

Active matter has become a quickly evolving field spanning from biology and physics to chemistry and engineering. Its defining property is the directed motion—translational, rotational, or both—of its constituents. This directed motion requires the steady input of free energy. Freed from the constraints of thermal equilibrium, active matter exhibits a wide range of novel phenomena; on the level of its single constituents up to emergent many-body collective and dynamic behavior. Extensively studied have been the aggregation of active particles into clusters, swarms, and other highly collective and dynamics states; but also spontaneous flow states where sufficiently high activity triggers the transition from a quiescent to a flowing fluid. At high densities, chaotic behavior has been reported in suspensions of bacteria and in numerical simulations. The aim of this project is to develop a comprehensive multiscale framework that bridges the properties of single particles to the large-scale chaotic flows. This framework will combine fully hydrodynamic simulations on the smallest scale with effective “dry” models on intermedium, and a continuum two-phase model on the coarsest scale. These approaches are complemented by statistical modeling aiming to uncover symmetries that can be exploited to further simply the effective and continuum models. During the first funding period of this project (second funding period of the TRR), we have successfully implemented and numerically investigated a model system of elliptic particles propelled by stress-boundary conditions. This has allowed us to already simulate particle pairs and small suspensions with full hydrodynamic details. In a parallel study, we have investigated the collective behavior of elliptic particles using implicit solvent simulations with effective interactions. Moreover, the basic equations for a detailed statistical analysis have been derived. The objective of the next funding period is to converge the different efforts into a comprehensive theoretical and numerical framework to model suspensions of active particles, bridging the scales from near-field hydrodynamic interactions to the macroscopic flow behavior.

Force Generation in Confined Active Fluids: The Role of Microstructure
Paul, Shuvojit and Jayaram, Ashreya and Narinder, N and Speck, Thomas and Bechinger, Clemens
Physical Review Letters 129, 058001, (2022)
see publication

Hunting active Brownian particles: Learning optimal behavior
Marcel Gerhard, Ashreya Jayaram, Andreas Fischer, and Thomas Speck
Physical Review Letters 104, 054614, (2021)
see publication

Probability theory of active suspensions
B. Deußen, M. Oberlack, Y. Wang
Physics of Fluids 33 (6), 061902 (2021)
see publication

Vorticity Determines the Force on Bodies Immersed in Active Fluids
Thomas Speck, Ashreya Jayaram
Physical Review Letters 126 (13), (2021)
see publication

High-order simulation scheme for active particles driven by stress boundary conditions
B Deußen, A Jayaram, F Kummer, Y Wang, T Speck, M Oberlack
Journal of Physics: Condensed Matter33 (24),244004 (2021)
see publication

Quorum-sensing active particles with discontinuous motility
Andreas Fischer, Friederike Schmid, Thomas Speck
Physical Review E101 (1), 012601 (2020)
see publication

From scalar to polar active matter: Connecting simulations with mean-field theory
Ashreya Jayaram, Andreas Fischer, Thomas Speck
Physical Review E101 (2), (2020)
see publication

Statistical theory of helical turbulence
B. Deußen, D. Dierkes, and M. Oberlack
Physics of Fluids 32 (6), 065109 (2020)
see publication