Enhanced Entanglement Density and Its Implication on Chain Diffusion Dynamics at the Air/Polyethylene Melt Interface

All-atom molecular dynamics (MD) simulations at the air/polyethylene (PE) melt interface are performed to investigate the entanglement of polymer chains specific to the interfacial region. Before analyzing the entanglement, certain properties of the PE melt such as density, melting point, and glass transition temperature are examined, and the present model accurately reproduces these properties. The MD simulations reveal an enhancement of kink (entanglement) density in the subsurface region of the PE melt. Additionally, it is observed that the enhanced entanglement density exhibits temperature dependence, decreasing as the temperature increases. The influence of the enhanced entanglement density on the diffusion dynamics (mean square displacement) of the polymer chains is examined in the time scale of several tens of nanoseconds. The results confirm that the chain dynamics at the interfacial region are affected by the interface-specific entanglement in the time scale of a reptation-like regime.