Rheology of Ring Polymer Melts: From Linear Contaminants to Ring/Linear Blends

TL;DR

This study uses molecular dynamics simulations to systematically analyze how linear contaminants affect the rheology of ring polymer melts, revealing significant viscosity increases and diffusion changes at specific concentrations.

Contribution

It provides the first systematic simulation-based investigation of the rheological impact of linear contaminants in ring polymer melts with controlled architecture.

Findings

Linear contaminants increase zero-shear viscosity by 10% at about one-fifth of overlap concentration.

Viscosity doubles when equal amounts of rings and linear polymers are blended.

Ring diffusion decreases dramatically at this concentration, while linear polymer properties remain stable.

Abstract

Ring polymers remain a major challenge to our current understanding of polymer dynamics. Experimental results are difficult to interpret because of the uncertainty in the purity and dispersity of the sample. Using both equilibrium and non-equilibrium molecular dynamics simulations we have systematically investigated the structure, dynamics and rheology of perfectly controlled ring/linear polymer blends with chains of such length and flexibility that the number of entanglements is up to about 14 per chain, which is comparable to experimental systems examined in the literature. The smallest concentration at which linear contaminants increase the zero-shear viscosity of a ring polymer melt of these chain lengths by 10% is approximately one-fifth of their overlap concentration. When the two architectures are present in equal amounts the viscosity of the blend is approximately twice as large as that of the pure linear melt. At this concentration the diffusion coefficient of the rings is found to decrease dramatically, while the static and dynamic properties of the linear polymers are mostly unaffected. Our results are supported by a primitive path analysis.