Dynamics and rheology of ring-linear blend semidilute solutions in extensional flow. Part I: Modeling and molecular simulations

Abstract

We use Brownian dynamics (BD) simulations and single molecule experiments to investigate the influence of topological constraints and hydrodynamic interactions on the dynamics and rheology of solutions of ring-linear polymer blends at the overlap concentration. We find agreement between simulation and experiment in which rings in solution blends exhibit large conformational fluctuations. A subpopulation of rings shows extension overshoots in the startup of the flow, and other populations display tumbling and tank-treading at the steady state. Ring polymer fluctuations increase with the blend fraction of linear polymers and are peaked at a ring Weissenberg number WiR≈1.5. On the contrary, linear and ring polymers in pure solutions show a peak in fluctuations at the critical coil-stretch Weissenberg number Wi=0.5. BD simulations show that extension overshoots on the startup of the flow are due to flow-induced intermolecular ring-linear polymer hooks, whereas fluctuations at the steady state are dominated by intermolecular hydrodynamic interactions (HIs). This is supported by simulations of bidisperse linear polymer solution blends, which show similar trends in conformational dynamics between rings and linear polymers with a matched contour length. Compared to BD simulations, single molecule experiments show quantitatively larger fluctuations, which could arise because experiments are performed on higher molecular weight polymers with stronger topological constraints. To this end, we have advanced the understanding of the effects of topological interactions and intermolecular HIs on the dynamics of semidilute ring-linear polymer blend solutions.

Investigating the Transition between Polymer Melts and Solutions in Nonlinear Elongational Flow

“…As it has been discussed in refs, − a different concentration dependence of the steady viscosity could also be due to the emergence of local hydrodynamics when diluting the polymer chains, with the oligomers acting more and more like a good solvent. However, as it is shown in ref , the same steady viscosity is found if oligomers are replaced by short entangled chains (PS chains of 73 kg/mol).…”

Materials Design of Highly Branched Bottlebrush Polymers at the Intersection of Modeling, Synthesis, Processing, and Characterization

“…Bottlebrush solutions are even more challenging; many of the same difficulties will apply as in melts; however, hydrodynamics will be possibly important to molecular relaxation at both the molecular and branch levels. Recent work on branched ,− and ring polymers − has demonstrated the key role that hydrodynamics plays in polymer solutions, even at relatively high concentrations where screening has often been thought to be dominant. , Indeed, driven polymer systems can move significantly outside the typical equilibrium framework where scaling arguments are used; this can lead to marked conformational fluctuations that are dictated by the local hydrodynamic environment, even in situations well above the overlap concentration. , Modeling these hydrodynamic interactions remains a key challenge in polymer simulations, due to the expense of satisfying fluctuation dissipation in implicit solvent representations and the long-range nature of these interactions that complicates periodic simulation boxes . Some standard methods, however, show promise.…”

“…384,390 Indeed, driven polymer systems can move significantly outside the typical equilibrium framework where scaling arguments are used; this can lead to marked conformational fluctuations that are dictated by the local hydrodynamic environment, even in situations well above the overlap concentration. 383,384 Modeling these hydrodynamic interactions remains a key challenge in polymer simulations, due to the expense of satisfying fluctuation dissipation in implicit solvent representations and the long-range nature of these interactions that complicates periodic simulation boxes. 391 Some standard methods, however, show promise.…”

To thread or not to thread? Effective potentials and threading interactions between asymmetric ring polymers

“…The passive ring threading by linear chains is even more evident in nonlinear rheology, in shear or extensional flows. 43,46–48 In other systems, the relevance of (active or passive) threadings, or lack thereof, is manifested too. Tadpole-shaped polymers exhibit a strong slow-down as a function of the tail length due to head-tail threadings.…”