Berlin 2018 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 9: Statistical Physics far from Thermal Equilibrium
DY 9.9: Vortrag
Montag, 12. März 2018, 12:15–12:30, BH-N 334
Oscillating Modes of Driven Colloids in Overdamped Systems — •Johannes Berner1, Boris Müller2,3, Juan Ruben Gomez-Solano1, Matthias Krüger2,3, and Clemens Bechinger1 — 1Physics Department, University of Konstanz, 78457 Konstanz, Germany — 24th Institute for Theoretical Physics, University of Stuttgart, 70569 Stuttgart, Germany — 3Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany
Microscopic particles suspended in liquids are the prime example of an overdamped system because viscous forces dominate over inertial effects. Apart from their use as model systems, they receive considerable attention as sensitive probes from which forces on molecular scales can be inferred. The interpretation of such experiments rests on the assumption, that, even if the particles are driven, the liquid remains in equilibrium, and all modes are overdamped. Here, we experimentally demonstrate that this is no longer valid when a particle is forced through a viscoelastic fluid. Even at small driving velocities where Stokes law remains valid, we observe particle oscillations with periods up to several tens of seconds. We attribute these to non-equilibrium fluctuations of the fluid, which are excited by the particle's motion. The observed oscillatory dynamics is in quantitative agreement with an overdamped Langevin equation with negative friction-memory term and which is equivalent to the motion of a stochastically driven underdamped oscillator. This fundamentally new oscillatory mode has considerable implications on how molecular forces are determined by colloidal probe particles under natural viscoelastic conditions.