Dresden 2026 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 56: Molecular and Polymer Dynamics, Friction and Rheology I

CPP 56.4: Talk

Friday, March 13, 2026, 11:45–12:00, HÜL/S386

Knots in Polymers under Shear Flow — •Maurice P. Schmitt¹, Andrey Milchev², and Peter Virnau¹ — ¹Institut für Physik, Johannes Gutenberg-Universität, Mainz, Germany — ²Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria

Knots in polymers and biological macromolecules, such as DNA and proteins, are crucial to their structure and function. However, the effect of external forces on knots in polymers is still insufficiently understood. Here, we investigate the impact of shear and Poiseuille flow on knotted flexible polymers using Molecular Dynamics (MD) and Multi-Particle Collision Dynamics (MPCD) simulations. We find that under simple shear (Couette flow), initially loose knots in polymer coils tighten beyond a critical shear rate. Further increase of the shear rate leads to tumbling motions of the chains in flow and fluctuating knot sizes. In contrast, knotted polymer globules subjected to shear unfold into pearl-necklace-like conformations, whereby knots spread across multiple sub-globules and undergo dynamic topological transitions. In Poiseuille flow, knots also tighten under increasing flow strength, with fluctuations in knot size emerging at high shear rates. Unexpectedly, the slit thickness significantly influences the tightening process even at constant mean shear rate. These findings reveal that both Couette and Poiseuille flow induce major structural and topological transformations in knotted polymers, offering insight into the behavior of knots under hydrodynamic forces in confined and driven environments.

Keywords: Polymers; Knots; Shear; Tumbling; Poiseuille