Regensburg 2022 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 49: Statistical Physics: General

DY 49.5: Vortrag

Freitag, 9. September 2022, 10:30–10:45, H20

Recoil experiments determine the eigenmodes of viscoelastic fluids — •Karthika Krishna Kumar¹, Félix Ginot¹, Juliana Caspers², Luis Reinalter¹, Matthias Krüger², and Clemens Bechinger¹ — ¹Fachbereich Physik, Universität Konstanz, Germany — ²Institute for Theoretical Physics, Georg-August Universität Göttingen, Germany

Probing viscoelastic media using colloidal particles reveals their complex relaxation processes at the microscopic level. Unlike Newtonian fluids, viscoelastic fluids can store and dissipate energy on much longer timescales because of their microstructure, therefore, these materials play a significant role in many technical applications. In this work, we perturb a viscoelastic fluid by driving a colloidal particle through the fluid using an optical tweezer. On deforming the viscoelastic matrix, the fluid tries to relax back by pushing the particle to recoil when the trap is turned off. The trajectory of such a recoiling particle exhibits a bi-exponential behavior indicating two distinct relaxation processes of the fluid. Detailed investigation shows that a microscopic model, with two fictitious bath particles connected to the probe particle via harmonic springs, explains the observed behavior. The analytical solution to the model also reveals two more timescales corresponding to the relaxation of the bath particles when the probe is fixed. The need for two bath particles to explain the results can be justified by considering the fluid as a glassy system, however, further experiments are required to confirm this.