Molecular Simulations of Controlled Polymer Crystallization in Polyethylene

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Crystallization of polymers from the melt is fundamental to material properties.
• Understanding the influence of molecular architecture and processing conditions on crystal morphology is crucial.
• Previous studies often lacked the resolution to observe early-stage crystal formation in detail.

Purpose of the Study:

• To investigate the formation of multilamella polymer crystals from the melt using molecular dynamics simulations.
• To explore the impact of polymer chain branching and crystallization protocols on crystal structure.
• To elucidate the early stages of spherulite formation and crystallite evolution.

Main Methods:

• Molecular dynamics simulations employing a united-monomer model with over 1.5 million monomers.
• Simulation of two-component polymer systems with varying long and short chain ratios and short butyl branches.
• Application of two distinct cooling protocols: continuous cooling and self-seeding.

Main Results:

• Successful growth of multilamella polymer crystals from the melt, a first in simulations.
• Drastically different multilamella structures observed based on branch content and cooling protocol.
• Self-seeding protocol yielded well-aligned crystals, clearly showing branching effects on crystallite size and shape.
• Continuous cooling obscured the subtle effects of branching on early spherulite formation.
• Extended chain segments (up to 100 monomers) observed within crystalline lamellae.

Conclusions:

• The crystallization protocol significantly dictates the resulting multilamella polymer crystal morphology.
• Polymer chain branching subtly influences crystallite evolution, particularly evident under self-seeding conditions.
• Molecular dynamics simulations provide a powerful tool to study complex polymer crystallization phenomena at the molecular level.