Dresden 2026 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 10: Droplets, Wetting, and Microfluidics (joint session DY/CPP)

CPP 10.11: Talk

Monday, March 9, 2026, 17:45–18:00, ZEU/0118

Experimentally probing microscale torsional memory in a viscoelastic fluid — •Niloyendu Roy¹, Rupayan Saha², Debankur Das², Matthias Krüger², and Clemens Bechinger¹ — ¹Fachbereich Physik, Universität Konstanz, Konstanz, Germany — ²Institut für Theoretische Physik, Universität Göttingen, Göttingen, Germany

Motion of a colloid inside viscoelastic fluids follows non-Markovian dynamics, meaning its trajectory is influenced by past motion. Such memory effects are typically attributed to intrinsic material timescales arising from relaxation of the fluid microstructure and are usually probed using translationally driven colloids. Here we show experimentally that rotational driving of a colloid by a controlled torque elicits a far richer form of memory: the relaxation of the resulting torsional stresses spans a broad distribution of timescales, even though the fluid itself possesses a single dominant relaxation time. This behaviour allows time-dependent torsional driving histories to be encoded and subsequently read out through characteristic non-monotonic recoil responses. By mapping the flow field and the spatial distribution of torsional stresses, we demonstrate that the geometry of rotation generates an orthogonality between the propagation of angular momentum and the storage of torsional stresses, producing a spatio-temporal memory field not accessible through translational forcing. These results establish torsional driving as a powerful route to generate, store, and retrieve memory in viscoelastic fluids, opening new possibilities for soft-matter information storage and torque-responsive microdevices.

Keywords: Non-Markovian fluid; Non-monotonic relaxation; Microscale torsion; Geometry and memory; Time-dependent phenomena