Granular Matters
MEGraMa: An experiment with magnetically excited granular particles on a research rocket. The dynamics of these particles can be investigated both with and without propulsion. Granular matter is defined as a collection of particles that are large enough for thermal motion to become insignificant and for dissipation to dominate the dynamics when the particles collide. Granular matter is relevant in many applications as well as for the fundamental understanding of many-body systems.
The macroscopic behaviour of granular systems is investigated by interweaving theory, simulation and experiments. This is done on the basis of particle-level properties such as dissipative interactions, particle shape and size as well as charges and system composition.
With increasing density, granular gases, granular liquids and granular packings are discussed in the context of the statistical physics of disordered media that transition from equilibrium to non-equilibrium states. For granular gases, magnetic forces can be used as a thermostat in microgravity, allowing for dynamics that are similar to, yet different from, thermal motion. As a result, many aspects of the dynamics of granular gases can be investigated to support and verify the development of textbook knowledge in this area.
For denser systems, light scattering and rheology are used to study excited granular fluids. Both conventional laser sources and terahertz radiation are used to capture structure and dynamics in this regime. The Soft-Matter Dynamics scattering experiment was installed on board the International Space Station ISS by Alexander Gerst in 2018.
The densest state of granular packings is defined by individual particles that form permanent contacts: The contacts can be monitored quantitatively by stress birefringence in both 2D and 3D. The behaviour of the whole system is also measured by sound, which becomes increasingly slower as the pressure on the cluster decreases. To avoid gradients, experiments are also carried out in microgravity.
Experiments in the group are complemented and motivated by microscopic theories for granular fluids and granular rheology. Similarly, numerical simulation is used to investigate fundamental predictions and to extend the otherwise inaccessible parameter space.
Research on granular matter at the institute is currently focussed on:
- Understanding the macroscopic properties of granular matter from particle-particle interactions
- Microgravity and laboratory experiments for granular gases, liquids and packings
- Theory and experiments on granular rheology