Hydrodynamic Inflation of Ring Polymers under Shear

TL;DR

This study reveals that ring polymers exhibit unique hydrodynamic inflation under shear, leading to self-stabilization and swelling effects not seen in other architectures, with implications for knot tightening.

Contribution

It introduces the discovery of shear-induced inflation and stabilization in ring polymers due to hydrodynamic interactions, highlighting effects exclusive to topology.

Findings

Ring polymers inflate and stabilize under shear due to hydrodynamic pockets.

Knots on rings tighten and localize under strong shear, affecting polymer configurations.

High contour length knotted rings behave similarly to unknotted rings of the same length.

Abstract

Hydrodynamic interactions as modeled by Multi-Particle Collision Dynamics can dramatically influence the dynamics of fully flexible, ring-shaped polymers in ways not known for any other polymer architecture or topology. We show that steady shear leads to an inflation scenario exclusive to ring polymers, which depends not only on Weissenberg number but also on contour length of the ring. By analyzing velocity fields of the solvent around the polymer, we show the existence of a hydrodynamic pocket which allows the polymer to self-stabilize at a certain alignment angle to the flow axis. This self-induced stabilization is accompanied by transitioning of the ring to a non-Brownian particle and a cessation of tumbling. The ring swells significantly in the vorticity direction, and the horseshoe regions on the stretched and swollen ring are effectively locked in place relative to the ring's center-of-mass. The observed effect is exclusive to ring polymers and stems from an interplay between hydrodynamic interactions and topology. Furthermore, knots tied onto such rings can serve as additional "stabilization anchors". Under strong shear, the knotted section is pulled tight and remains well-localized while tank-treading from one horseshoe region to the opposite one in sudden bursts. We find knotted polymers of high contour length behave very similarly to unknotted rings of the same contour length, but small knotted rings feature a host of different configurations. We propose a filtering technique for rings and chains based on our observations and suggest that strong shear could be used to tighten knots on rings.