SCM Seminar
Out-of-Equilibrium Dynamics of Synthetic and Living Matter in Complex Environments
Speaker: Narinder (Department of Physics and Astronomy, University of Potsdam, Germany)
In this talk, I will present the experimentally observed dynamics of active (i.e., self-propelled) colloidal particles in viscoelastic fluids with stress-relaxation times on the order of seconds. In such fluids, the active particle dynamics lack a clear-cut separation of timescales from those of their surroundings, leading to striking features such as diffusion coefficients enhanced by orders of magnitude and spontaneous persistent circular motion that have no counterpart in purely viscous environments [1].
Furthermore, I will discuss how additional physical constraints, such as rigid boundaries, influence their dynamics. Our results reveal that the interplay between self-propulsion and fluid elasticity mediates long-range repulsive interactions and rapid reorientation, which stand in stark contrast to the persistent wall-accumulation typically observed in purely viscous environments [2].
I will also present experimental results demonstrating that the above-mentioned effects are not specific to our self-propulsion mechanism or to a particular kind of viscoelastic fluid, but are rather general; they occur for externally driven colloidal particles and even for active particles moving within a colloidal glassy environment [3,4].
Finally, I will discuss recent experimental quantifications of out-of-equilibrium fluctuations within the cortex of living cells, characterized via Atomic Force Microscopy (AFM). Our findings suggest that while the concept of 'effective temperature' is a common proxy for measuring the distance from equilibrium, it can fail to accurately capture the true state of the system. Instead, we demonstrate that time irreversibility and entropy production rates are more robust signatures of non-equilibrium dynamics in biological matter [5].
References
[1] N Narinder, C Bechinger, JR Gomez-Solano, Physical review letters 121, 078003 (2018)
[2] N Narinder, JR Gomez-Solano, C Bechinger, New Journal of Physics 21, 093058 (2019)
[3] N Narinder, MF Bos, C Abaurrea-Velasco, J de Graaf, C Bechinger, Soft Matter 18, 6246 (2022)
[4] N Narinder, J Behera, A Ghosh, arXiv preprint arXiv:2406.14505 (2024)
[5] N Narinder, E Fischer-Friedrich, Physical Review X 16, 011007 (2026)