Ali Seyedi | Searcharxiv

arXiv2026

Odd Polycatenanes Tank-Tread in Strong Shear Flow

Polycatenanes are mechanically interlocked polymers composed of ring molecules linked through mechanical bonds. Here, we investigate the single-molecule dynamics of linear polycatenanes under strong steady shear flow using coarse-grained Brownian dynamics simulations with hydrodynamic interactions. We identify a stable tank-treading state in which individual rings rotate continuously while the overall polymer remains highly extended and aligned with the flow direction, adopting conformations typically associated with extensional flow. Remarkably, tank-treading is observed almost exclusively in odd polycatenanes, polycatenanes with an odd number of rings. We attribute this odd-even effect to the orientation of the terminal rings within the flow-gradient plane, where they act as anchors that stabilize polymer extension, a configuration accessible only to odd polycatenanes. Furthermore, our simulations and a Markov state model demonstrate that this dynamic behavior remains stable over long timescales. Finally, we show that tank treading polycatenanes can be used to fully extend other molecules in strong shear flow, hinting at applications of this behavior to manipulate molecules in rotational flows.

cond-mat.soft↗

arXiv2025

Mechanically Interlocked Polymers in Dilute Solution under Shear and Extensional Flows: A Brownian Dynamics Study

Mechanically interlocked polymers (MIPs) are a novel class of polymer structures in which the components are connected by mechanical bonds instead of covalent bonds. We measure the single-molecule rheological properties of polyrotaxanes, daisy chains, and polycatenanes under steady shear and steady uniaxial extension using coarse-grained Brownian dynamics simulations with hydrodynamic interactions. We obtain key rheological features, including tumbling dynamics, molecular extension, stress, and viscosity. By systematically varying structural features, we demonstrate how MIP topology governs flow response. Compared to linear polymers, all three MIP architectures exhibit enhanced tumbling in shear flow and lower normal stress differences in extensional flow. While polyrotaxanes show higher shear and extensional viscosities, polycatenanes and daisy chains have lower viscosities. In extensional flow, polyrotaxanes and polycatenanes extend earlier than linear polymers. We find that mechanical bonds suppress shear thinning and alter the coil-stretch transition observed in linear polymers. These effects arise from the mechanically bonded rings in MIPs, which expand the polymer profile in gradient direction and increase backbone stiffness due to ring-backbone repulsions. This study provides key insights into MIP flow properties, providing the foundation for their systematic development in engineering applications.

cond-mat.soft↗