Spatial correlations of entangled polymer dynamics

TL;DR

This study investigates the spatial correlations in entangled polymer dynamics using simulations and spectroscopy, revealing limitations of existing models and highlighting the importance of incompressibility in polymer melt behavior.

Contribution

It provides new insights into the spatial correlations of entangled polymers and challenges the validity of traditional models like the tube model.

Findings

Long tail in reciprocal-space correlations indicating dynamic localization

Existing models cannot fully describe observed spatial correlations

Incompressibility may play a critical role in melt dynamics

Abstract

The spatial correlations of entangled polymer dynamics are examined by molecular dynamics simulations and neutron spin-echo spectroscopy. Due to the soft nature of topological constraints, the initial spatial decays of intermediate scattering functions of entangled chains are, to the first approximation, surprisingly similar to those of an unentangled system in the functional forms. However, entanglements reveal themselves as a long tail in the reciprocal-space correlations, implying a weak but persistent dynamic localization in real space. Comparison with a number of existing theoretical models of entangled polymers suggests that they cannot fully describe the spatial correlations revealed by simulations and experiments. In particular, the strict one-dimensional diffusion idea of the original tube model is shown to be flawed. The dynamic spatial correlation analysis demonstrated in this work provides a useful tool for interrogating the dynamics of entangled polymers. Lastly, the failure of the investigated models to even qualitatively predict the spatial correlations of collective single-chain density fluctuations points to a possible critical role of incompressibility in polymer melt dynamics.