Ring conformations in bidisperse blends of ring polymers

TL;DR

This study uses computer simulations to analyze the conformations of ring polymers in bidisperse blends, revealing how entanglements and topological interactions influence ring sizes and correlations.

Contribution

It introduces a detailed analysis of ring conformations in bidisperse blends, highlighting the role of penetrable surface fractions and bond-bond correlations, challenging recent proposals about variable entanglement lengths.

Findings

Compression of entangled rings explained by penetrable surface fraction changes.

Bond-bond correlations show anti-correlation peaks at specific distances.

Entanglement length in ring melts remains constant for large polymers.

Abstract

The size of rings (also called cyclic polymers) in bidisperse blends of chemically identical rings is analyzed by computer simulations. Data of entangled ring blends and blends of interpenetrating rings are compared and it is shown that the compression of entangled rings can be explained by the changes in the penetrable fraction of the minimal surface bounded by the ring. Corrections for small rings can be approximated by a concatenation probability $1-P_{OO}$ that a ring entraps at least one other ring. Both results are in line with a previous work [1] to explain the compression of entangled rings in monodisperse melts. Bond-bond correlations in melts of interpenetrating rings lead to similar corrections for ring sizes as reported previously [2] for monodisperse linear melts. For entangled rings, bond-bond correlations show an anti-correlation peak at a curvilinear distance of about ten segments that coincides with a horizontal tangent in the normalized mean square internal distances along the ring. Both observations become independent of melt molecular weight for sufficiently large degrees of polymerization and such behavior is not found in samples with entanglements switched off. In consequence, the length scale of topological interactions (entanglement length) in a melt of entangled rings must be considered as constant in contrast to a recent proposal by Sakaue [3].