Shear-thinning in Polymer Melts -- Molecular Origins and Hybrid Multiscale Simulations

TL;DR

This study combines molecular and macroscopic simulations to understand how molecular alignment, stretching, and tumbling contribute to shear-thinning in polymer melts, emphasizing the role of molecular structure in flow behavior.

Contribution

It introduces a multiscale simulation approach linking molecular dynamics with continuum models to elucidate shear-thinning mechanisms in polymer melts.

Findings

Molecular alignment and tumbling influence shear-thinning.

Interchain interactions contribute to collective phenomena.

Microscopic details like chain flexibility affect macroscopic flow.

Abstract

We investigate the molecular origin of shear-thinning in melts of flexible, semiflexible and rigid oligomers with coarse-grained simulations of a sheared melt. Alignment, stretching and tumbling modes or suppression of the latter all contribute to understanding how macroscopic flow properties emerge from the molecular level. By performing simulations of single chains in a shear flow, we identify which of these phenomena are of collective nature and arise through interchain interactions and which are already present in dilute systems. Building upon these microscopic simulations we identify by means of the Irving-Kirkwood formula the corresponding macroscopic stress tensor for a non-Newtonian polymer fluid. Shear-thinning effects in oligomer melts are also demonstrated by macroscopic simulations of a channel flow. The latter have been obtained by the discontinuous Galerkin method approximating macroscopic polymer flows. Our study confirms the influence of microscopic details in the molecular structure of short polymers such as chain flexibility on macroscopic polymer flows.