Summary

Active matter systems are driven out of equilibrium by a local influx and dissipation of energy, in many cases leading to self-propelled particle motion. The collective dynamics of active matter systems is characterized by a variety of notable phenomena that are impossible in equilibrium thermodynamics. In recent years, it has been found that topological defects occurring in active matter are very useful for characterizing these collective phenomena, and in particular also for controlling them. This has been widely studied in the physics of active nematics, but much less in systems of particles with self-propelled constituents. In this project, we plan to study the emergence and dynamics of topological defects in systems of ellipsoidal active particles moving orthogonal to their symmetry axis. Based on theoretical arguments from algebraic topology developed in unpublished preliminary work, we hypothesize the existence of novel types of topological defects in this system. In the  project, we will first investigate the bulk phase diagram of the ellipsoids via Brownian dynamics simulations. Thereby having identified promising regions in parameter space, we will in the second step perform simulations of confined systems, as the confinement is expected to promote the emergence of various types of defects. This allows us to study the different defect types and their dynamics. Using recently developed theoretical methods, we will in a third step investigate the local entropy production in the system to assess to what extend defects contribute to the entropy production of the active system. In parallel to these simulation studies, we will perform theoretical investigations on topological methods for the analysis of defect structures in smectics, which will allow us to classify also defects in smectic phases we expect to find in the system. Since similar defects and phases are can also be found in block copolymer systems, we will apply this method also to the defect structures studied in project C02, which studies block copolymers.
The project serves the central mission of the CRC 1552: Understand the influence of defects on the dynamics (collective phenomena) and properties (entropy production) of soft matter systems (active matter), control them (via confinement), and use them for new functional devices (cargo manipulation).