Local dynamics and primitive path analysis for a model polymer melt near a surface

TL;DR

This study investigates how surfaces influence the local dynamics, entanglement, and viscosity of polymer melts, revealing that surface interactions can accelerate or slow chain motion and modify entanglement density, affecting mechanical properties.

Contribution

It provides new insights into how surface chemistry and grafted chains alter polymer chain dynamics and entanglement near interfaces, combining primitive path and Rouse mode analyses.

Findings

Repulsive walls accelerate chain dynamics and reduce entanglement density.

Grafted chains can slow down dynamics in entangled regimes and increase entanglement density.

Surface modifications can enhance mechanical reinforcement of polymer melts.

Abstract

By applying local primitive path and Rouse modes analysis we study the chains conformations, local dynamics and viscosity of a model polymer melt in a polymer-wall interface. We establish that the presence of a repulsive wall leads to acceleration of the dynamics both for unentangled and weakly entangled melts and to a depletion in the entanglement density in the wall vicinity. When the surface bears some grafted chains, we show that the melt chains are accelerated in the unentangled regime and slowed down in the entangled regime. By analyzing the primitive paths we attribute the observed slowdown to an increase in the entanglement density in the interfacial layer. The presence of a relatively small density of grafting sites thus leads to improved mechanical properties (reinforcement) and decreases locally the entanglement length even if the surface is repulsive.