Entanglements in quiescent and sheared polymer melts

Area of Science:

• Polymer Physics
• Materials Science
• Computational Chemistry

Background:

• Polymer melts exhibit complex behavior due to chain entanglements, which are crucial for their mechanical properties.
• Understanding entanglement dynamics under flow is essential for predicting polymer melt processing and performance.
• Previous methods often struggle to visualize and quantify entanglements in dynamic simulations.

Purpose of the Study:

• To develop and apply a novel method for visualizing polymer entanglements in melts using molecular dynamics.
• To investigate the dynamic behavior of entanglements under applied shear flow.
• To correlate simulated entanglement dynamics with experimentally observed phenomena like stress overshoot.

Main Methods:

• Utilized molecular dynamics simulations to model polymer melts.
• Defined entanglements as 'hot spots' based on time-averaged interaction energy between beads and nonbonded neighbors.
• Applied shear flow at rates exceeding chain disengagement to observe entanglement evolution.

Main Results:

• Identified persistent 'hot spots' representing entanglements, characterized by high time-averaged interaction energies.
• Observed that under shear flow, entanglements deform into bent structures.
• Demonstrated that chain stretching and subsequent disentanglement, driven by bend propagation, lead to stress overshoot.

Conclusions:

• The 'hot spot' visualization method effectively captures polymer melt entanglements.
• Simulated entanglement dynamics under shear flow accurately reproduce key aspects of polymer melt rheology, including stress overshoot.
• This approach provides a powerful tool for understanding polymer entanglement mechanics.