Flow-induced density fluctuation assisted nucleation in polyethylene

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Polymer crystallization is crucial for material properties.
• Understanding nucleation mechanisms is key to controlling polymer structure.
• Shear flow is known to influence polymer crystallization kinetics.

Purpose of the Study:

• To comparatively study polyethylene nucleation under quiescent and shear flow conditions.
• To elucidate the distinct intermediate orders and kinetic pathways involved.
• To explain the significant acceleration of nucleation rates by shear flow.

Main Methods:

• All-atom molecular dynamics simulations were employed.
• Polyethylene nucleation was simulated under both quiescent and shear flow.
• Intermediate ordering and density fluctuations were analyzed.

Main Results:

• Nucleation is a two-step process under both conditions, but with different intermediate orders.
• Quiescent nucleation involves local order structures.
• Flow-induced nucleation is driven by density fluctuations from conformational and orientational ordering.

Conclusions:

• Shear flow promotes nucleation by facilitating conformational ordering and density fluctuations.
• Flow circumvents the entropic penalty, a rate-limiting step in quiescent crystallization.
• The accelerated nucleation rate under flow is attributed to a distinct kinetic pathway.