Composite Entanglement Topology and Extensional Rheology of Symmetric Ring-Linear Polymer Blends

TL;DR

This study uses molecular simulations to explore how the topology and composition of symmetric ring-linear polymer blends influence their entanglement structure, dynamics, and extensional rheology, revealing a maximum topological constraint at a specific blend ratio.

Contribution

It provides a detailed analysis of the entanglement topology and rheological behavior of symmetric ring-linear polymer blends, highlighting the role of blend composition in topological constraints and flow response.

Findings

Maximum topological constraints at a ring fraction of about 0.4.

Extensional stress overshoot linked to ring unthreading during flow.

Significant changes in entanglement structure during flow observed and quantified.

Abstract

Extensive molecular simulations are applied to characterize the equilibrium dynamics, entanglement topology, and nonlinear extensional rheology of symmetric ring-linear polymer blends with systematically varied ring fraction $\phi_R$. Chains with degree of entanglement $Z\approx14$ mixed to produce 10 well-entangled systems with $\phi_R$ varying from neat linear to neat ring melts. Primitive path analysis are used to visualize and quantify the structure of the composite ring-linear entanglement network. We directly measure the quantity of ring-linear threading and linear-linear entanglement as a function of $\phi_R$, and identify with simple arguments a ring fraction $\phi_R\approx0.4$ where the topological constraints of the entanglement network are maximized. These topological analyses are used to rationalize the $\phi_R$-dependence of ring and linear chain dynamics, conformations, and blend viscosity. Complimentary simulations of startup uniaxial elongation flows demonstrate the extensional stress overshoot observed in recent filament stretching experiments, and characterize how it depends on the blend composition and entanglement topology. The overshoot is driven by an overstretching and recoil of ring polymer conformations that is caused by the convective unthreading of rings from linear chains. This produces significant changes in the entanglement structure of blends that we directly visualize and quantify with primitive path analyses during flow.