On the Dynamics and Disentanglement in Thin and Two-Dimensional Polymer Films

TL;DR

This study uses molecular dynamics simulations to explore how confinement affects the dynamics and entanglement properties of two-dimensional and thin polymer films, revealing significant differences from bulk behavior.

Contribution

It provides new insights into the dynamics and entanglement length variations in 2D polymer melts and thin films under confinement, using primitive path analysis.

Findings

2D monomer mean-square displacement follows a $t^{8/15}$ law at intermediate times

Entanglement length $N_e$ increases as film thickness decreases

Dynamics in 2D melts differ qualitatively from thin films and bulk polymers

Abstract

We present results from molecular dynamics simulations of strictly two-dimensional (2D) polymer melts and thin polymer films in a slit geometry of thickness of the order of the radius of gyration. We find that the dynamics of the 2D melt is qualitatively different from that of the films. The 2D monomer mean-square displacement shows a $t^{8/15}$ power law at intermediate times instead of the $t^{1/2}$ law expected from Rouse theory for nonentangled chains. In films of finite thickness, chain entanglements may occur. The impact of confinement on the entanglement length $N_\mathrm{e}$ has been analyzed by a primitive path analysis. The analysis reveals that $N_\mathrm{e}$ increases strongly with decreasing film thickness.