Vibrationally Driven Motion of Active Granular Particles
Final Report Abstract
Self-propelled granular particles driven by vibrations are a novel and exciting system to study the properties of active matter experimentally. These particles show interesting collective behaviour, far beyond what is observed in thermal equilibrium. In this project the individual and collective motion of such particles has been measured, simulated and modelled analytically. Concerning the dynamics of individual particles an interesting connection to the bouncing ball problem was unravelled, where particles show a transition from periodic to chaotic tumbling motion. A monodisperse many-body system of self-spinning particles was prepared as a model for a homogeneously heated granular gas, where energy is injected into the system via the rotational degree of freedom. Dissipation during collisions with other particles leads to a non-Gaussian velocity distribution with overpopulated tails. This result is in accordance with fundamental analytical results from the theory of dissipative granular gases. A binary system with particles spinning in opposite directions shows a robust demixing at intermediate packing fractions, which was shown experimentally, for the rst time, using granular rotors. In this systems, particles also perform a directed motion at the interfaces, which leads to super-diffusive transport for particles at the edge of domains. Experiments were mapped to a Langevin dyanmics simulation which reproduces the experimental results with high accuracy. For a single self-propelled particle the Langevin dynamics model was also solved analytically, where the relevance of inertia was studied in great detail. It was shown, how mass and moment of inertia introduce an inertial delay to the dynamics, which affects the dynamics not only on short but also on long timescales.
Publications
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Ratcheting and tumbling motion of Vibrots, New J. Phys. 18.12 (2016): 123001
Christian Scholz, Sean D'Silva, Thorsten Pöschel
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Velocity distribution of a homogeneously driven two-dimensional granular gas, Phys. Rev. Lett. 118, 198003 (2017)
Christian Scholz, Thorsten Pöschel
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Inertial delay of self-propelled particles, Nature Communications 9, 5156 (2018)
Christian Scholz, Soudeh Jahanshahi, Anton Ldov, Hartmut Löwen
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Rotating robots move collectively and self-organize, Nature Communications 9, 931 (2018)
Christian Scholz, Michael Engel, Thorsten Pöschel
