Systematic coarse-graining of the dynamics of entangled polymer melts: the road from chemistry to rheology

TL;DR

This paper reviews various simulation techniques for linking the molecular structure of entangled polymers to their macroscopic rheological properties, focusing on different levels of coarse-graining and their capabilities.

Contribution

It provides a comprehensive assessment of current coarse-graining methods, comparing their ability to connect chemistry to rheology in entangled polymer melts.

Findings

CGMD prevents bond crossing but limits chain length.

CGSD allows higher coarse-graining but requires bond crossing prevention.

Primitive path analysis aids in understanding entanglement characteristics.

Abstract

For optimal processing and design of entangled polymeric materials it is important to establish a rigorous link between the detailed molecular composition of the polymer and the viscoelastic properties of the macroscopic melt. We review current and past computer simulation techniques and critically assess their ability to provide such a link between chemistry and rheology. We distinguish between two classes of coarse-graining levels, which we term coarse-grained molecular dynamics (CGMD) and coarse-grained stochastic dynamics (CGSD). In CGMD the coarse-grained beads are still relatively hard, thus automatically preventing bond crossing. This also implies an upper limit on the number of atoms that can be lumped together and therefore on the longest chain lengths that can be studied. To reach a higher degree of coarse-graining, in CGSD many more atoms are lumped together, leading to relatively soft beads. In that case friction and stochastic forces dominate the interactions, and actions must be undertaken to prevent bond crossing. We also review alternative methods that make use of the tube model of polymer dynamics, by obtaining the entanglement characteristics through a primitive path analysis and by simulation of a primitive chain network. We finally review super-coarse-grained methods in which an entire polymer is represented by a single particle, and comment on ways to include memory effects and transient forces.